Conjugated linoleic acid (CLA) has drawn significant attention in the last two decades for its various potent beneficial effects on human health, such as anticarcinogenic and antidiabetic properties. CLA could be generally found in ruminant products, such as milk. The amount of CLA in ruminant products mainly depends on the diet of the animals. In general, the fat content in the ruminant diet is low, and dietary fat supplementation can be provided to improve rumen activity and the fatty acid (FA) profile of meat and milk. Especially, dietary 18-carbon polyunsaturated FA (C18 PUFA), the dominant fat source for ruminants, can modify the milk FA profile and other components by regulating the ruminal microbial ecosystem. In particular, it can improve the CLA in milk, intensify the competition for metabolic hydrogen for propionate producing pathways and decrease methane formation in the rumen. Therefore, lipid supplementation appears to be a promising strategy to naturally increase the additional nutritional value of milk and contribute to lower methane emissions. Meanwhile, it is equally important to reveal the effects of dietary fat supplementation on rumen fermentation, biohydrogenation (BH) process, feed digestion, and microorganisms. Moreover, several bacterial species and strains have been considered to be affected by C18 PUFA or being involved in the process of lipolysis, BH, CLA, or methane emissions. However, no review so far has thoroughly summarized the effects of C18 PUFA supplementation on milk CLA concentration and methane emission from dairy cows and meanwhile taken into consideration the processes such as the microorganisms, digestibility, rumen fermentation, and BH of dairy cattle. Therefore, this review aims to provide an overview of existing knowledge of how dietary fat affects rumen microbiota and several metabolic processes, such as fermentation and BH, and therefore contributes to functional and low-carbon milk production. There is an increasing awareness of the relationship between health and diet among consumers, which leads to the nutritional quality of food becoming a hot topic. Functional foods, defined as foods or food components that have positive effects on human health beyond the basic nutritive value  became mDietary fatty acid (FA) supplementation has become a widely accepted dietary strategy for improving the quality of animal products –7. ThereOriginally, fat supplementation is used to improve the energy values of diets to meet the energy requirements of dairy cows but it is also found to have additional functions to modify the FA profiles of meat  and milkEven though the fat supplementation has beneficial effects on both milk CLA and environmental sustainability, the excess of addition would have negative effects on the rumen fermentation and feed digestibility. Generally, the effects mainly depend on the type and the dosage of fat supplemented , 22. ThuSo far, a few meta-analyses have focused on the response of fat to FA composition and methane emission of cattle –25. AddiThis review aims to provide an overview of the existing knowledge regarding the effect of dietary fat on milk CLA and methane emission from dairy cows, while considering several metabolic processes such as rumen fermentation, BH, and microbiota response. We believe that our study makes a significant contribution to the domain because fat supplementation is a promising dietary strategy to increase the special milk fat  and to produce low carbon milk (inhibit methane emissions) by ruminants and this review provides an detailed insight into those effects.Nowadays, people are highly interested in non-nutrients and natural nutrients that are present in foods that may have beneficial effects on humans health. CLA is one of these nutrients. CLA is an essential FA that has been shown to have anti-cancer properties in various studies in animal models . Principcis-9trans-11 C18:2 (c9t11CLA) from milk fat. It was also believed that CLA is not normally part of a cow’s diet, and it should be a result of ruminal BH of lipids  between the level of pasture grass consumption and CLA content in milk fat  or C18:3 PUFA (46% of FA) as the predominant FA. Especially, pasture-based diets fed to the dairy cow are rich in C18:3, representing 48–56% of total FA , compared to cows fed with the control diet  before incubation, PUFAth is the duodenal or omasal flow of PUFA (g) or PUFA (g) recovered in batch in vitro culture bottle after t (h) of incubation.where, PUFAHowever, this mechanism does not provide detailed knowledge of the nature of the accumulating CLA or other intermediates. Rumen FA metabolism is a multistep process that requires measures to assess the conversion efficiency of each step. Calculations are complex because of the movement of FAs among pools –55. AddiWe concluded that the addition of C18:2 or C18:3 PUFA in the diet of dairy cattle can increase milk CLA partially through the ruminal BH process pathway. However, the detailed knowledge of the formation mechanism in CLA and its conversion efficiency is still unclear.c9t11 CLA in milk comes from the endogenous synthesis in the mammary gland via a pathway related to the desaturation of vaccenic acid by the Δ9-desaturase enzyme. Studies show that the abomasum of a cow infused with vaccenic acid (12.5 g/d) for 3 days, can increase the CLA content of milk fat by 40%   . For lac removed . Howeverc9t11CLA.Even though the majority of the CLA from endogenous synthesis is not from the rumen BH, it is firmly believed that the addition of oils rich in C18:2 and C18:3 FA can increase the production of CLA in milk, since the rumen BH could enhance the vaccenic acid content which potentially being the additional substrate for the endogenous synthesis of the In summary, manipulating the diets of the cow by fat supplementation can increase the CLA contents of milk. However, it is still challenging to analyze and detect all of the isomers of CLA. It would be significant for future research to investigate the biological role of individual isomers.The effects of PUFAs on ruminal digestion of nutrients may vary, and the amount of forage used in the diet can be considered a key factor . InteracFrom the standpoint of rumen carbohydrate fermentation, BH is a favorable process because it reduces the potential negative effects of UFA on rumen fermentation of fiber. This suggests that UFAs are toxic to many species of rumen bacteria, especially those involved in fiber digestion . A decreIt has been shown that oil supplementation did not shift the crude protein (CP) digestibility . HoweverA diet supplemented with plant oil has a higher apparent digestibility of EE , 68. BauIn conclusion, the increase in dietary PUFAs did not have a negative influence on NDF degradability if the dosage of plant oil was relatively low (≤5% of dietary DM), and it may increase the apparent digestibility of CP and EE regardless of the dosage level .Ruminants acquire energy from the feed materials through microbial fermentation. During the fermentation process, energy is released as adenosine triphosphate, which is used to fuel the different activities of ruminal microorganisms. Energy levels can be increased by supplementing animals with dietary fat, an approach that has been widely used. However, the reported effect of oils on rumen fermentation varies dramatically among studies, depending on the concentration, origin, saturation degree, FA composition of the fats used, and the nutrient composition of the diets .in vivo  and changes the rumen fermentation pattern by increasing the proportion of propionate  supplementation in ruminant diets at a relatively high level (>5% of the DM) depressed the rumen ammonia concentration . ConversMethane production from ruminal anaerobic fermentation contributes to a 2–12% loss of the ingested gross energy  and greeMany methane inhibitory additives have been proven to affect methane production in ruminants, either by sequestering hydrogen , 111 or in vitro , bacterial cell synthesis (12%), and VFA synthesis (33%) (Unsaturated fatty acid may use hydrogen for the BH reaction and propionic acid production is associated with a decrease in methane production . Howeveris (33%) . Therefois (33%) , but preis (33%) . Dietaryis (33%) . Howeveris (33%) , indicatis (33%)  and Prinis (33%)  have shois (33%) , 127. ThDaily methane production from dairy cows varies among studies 400–500 g/d (methane: 1 L ≈ 0.7143 g) depending on the DM intake (DMI), milk yield, and diet type, and the methane production ranged from 18 to 25 g/kg DMI and 10 to 24 g/kg milk , 129. PUIt has been reported that there was 0.8–5.5% reduction in methane production in the fat supplementation group compared with that of the control group . This su2 = 0.64), which is higher than NDF (R2 = 0.42) and non-fibrous carbohydrate  as sole predictors. Concentrations of NDF and NFC (R2 = 0.79), NDF and fat (R2 = 0.73), NFC and fat (R2 = 0.95), and NDF, NFC, and fat (R2 = 0.80) could improve the methane prediction compared to single predictors. This suggests that using the concentrations of NFC and fat is the best approach to predict methane production, although the high prediction accuracy does not seem from a biological perspective, considering data were collected from several sources.Additionally, according to Patra , methaneThese results suggest that C18 PUFA supplementation can inhibit methane emission in the rumen by decreasing the number of ruminal protozoa and methanogens bacteria. However, the extent of the depression is majorly dependent on the unsaturation of PUFA, the amount of the PUFA addition, and the dietary type, but not on the lactation stage.In ruminant animals, most of the digestive and metabolic processes, such as organic matter (OM) fermentation, lipolysis, BH, and methane emissions, are involved in ruminal microbiotic activity, including bacteria, fungi, protozoa, and archaea. Despite a highly stable function because of functional resilience and redundancy of the ruminal microbial ecosystem , the rumEarly studies regarding oil supplementation in ruminant diets were primarily related to its toxicity toward protozoa. A dramatic decrease in the protozoan population occurred when the diet was supplemented with three different C18 UFAs: OA (C18:1), ALA (C18:3), and LA (C18:2) . The inhSelenomonas ruminantium and Prevotella ruminicola  were not adversely affected by OA, while B. fibrisolvens and Ruminococcus, which are mainly related to acetate and butyrate production, were inhibited by OA. Further studies on pure strain cultures showed that LA inhibits the growth of B. fibrisolvens A38 at very low concentrations (4 mg/L)  , and thacultures . This suposition –150. Forposition . Furtherposition , and a hposition , 151. Inposition . This inposition . HoweverNeocallimastix frontalis (in vivo study revealed that LA supplementation adversely affected the order Neocallimastigales, whose abundance and diversity was reduced by soybean oil supplementation (The effects of oil supplementation on rumen fungi have rarely been reported, but it is still recognized that the addition of PUFAs can affect fungi. In pure cultures, LA alters the growth of the fungus rontalis . A previentation .In general, the supplementation of PUFA can decrease the number of protozoa and bacteria, and potentially reduce the fungi abundance. These effects on microorganisms mainly depend on the quantity and type of fat supplemented. In addition, there is still limited knowledge about the effect of PUFA on fungi, and the further investigation using the new technology is necessary.Lipolysis occurs rapidly after food intake in ruminal animals , 155. ThAnaerovibrio lipolyticus is a well-known triacylglycerol-hydrolyzing bacterium (A. lipolytica is dominates the ruminal lipase activity in animals receiving concentrated feed and lacks the ability to hydrolyze galactolipids and phospholipids. Therefore, other lipolytic species are expected to predominate in the rumens of grazing animals. It has been confirmed that galactolipids and phospholipids could be hydrolyzed by some strains B. fibrisolvens (Butyrivibrio-like species (Butyrivibrio spp. seemed to contain phospholipase A, phospholipase C, phosphodiesterase, and lysophospholipase activities typical of mixed rumen contents (Despite the abundant diversity of ruminal microorganisms, bacteria are considered to be the most active in lipolysis. This view was supported by experiments with ciliate-free sheep, in which the hydrolysis of phosphatidylcholine was high . Anaerovacterium , 160, whisolvens  and Buty species , 162. Bucontents . In factcontents .Epidinium spp. accounted for 30–40% of lipolytic activity in the rumen. Epidinium ecaudatum has galactosidase activity and is capable of releasing galactose from galactolipids (Entodinium caudatum, was observed to have phospholipase activity (However, the lipolytic activity of protozoa has not been extensively studied. Wright  reportedtolipids . Anotheractivity  which apactivity .Clostridium, Propionibacterium, Selenomonas, and Staphylococcus genera (Pseudomonas aeruginosa strain (Recent data have shown that lipolytic activity is involved in other rumen bacteria, including s genera , as wella strain . Recent a strain  identifiIt is well-known that the BH of PUFAs is a characteristic biochemical reaction driven by ruminal microbiota. Pioneering studies have reported that rumen microorganisms are capable of hydrogenating C18:1, C18:2, and C18:3 PUFAs to form C18:0 SFAs –173.Protozoa account for approximately 50% of the ruminal microbial biomass and about 75% of the microbial FAs present in the rumen originate from protozoa . TherefoB. fibrisolvens can convert LA to trans C18:1 but not to C18:0 (B. fibrisolvens also hydrogenates LA to trans intermediates (B. hungatei can also convert LA to OA. Additionally, Paillard et al. (Butyrivibrio isolates, and a large number were capable of metabolizing LA to OA. Minor differences in BH pathways among strains were also reported by Fukuda et al. (MDT-5, MDT-10, and A38 strains could metabolize LA to trans-11 cis-13 CLA, OA, and trans-11 cis-15 C18:2, respectively.It has been shown that to C18:0 . Moreovemediates . Maia etmediates  found thd et al.  and Hussd et al.  demonstra et al. , who fouB. fibrisolvens, producing trans-11 UFA. Kepler and Tove (B. fibrisolvens D12 isomerase is localized in membranes or tightly attached to bacterial membranes. Its substrates are FA with a free carboxyl function and double bonds on cis-9 and cis-12 carbons (cis-9 trans-11 CLA, such as Bifidobacterium, Clostridium, Pseudobutyrivibrio, Lactobacillus, Propionibacterium, Eubacterium, Roseburia, Enterococcus, and Pediococcus genera (Streptococcus bovis. Several strains of Streptococcus, Staphylococcus, Lactobacillus, Enterococcus, and Pediococcus can catalyze this reaction (Ruminococcus albus F2/6 (M. elsdenii YJ-4 and M. elsdenii T81, could convert C18:2 to trans-10 cis-12 CLA in the rumen of a cow fed a high-starch diet (The first step of BH was isomerization by and Tove  reported carbons . Other bs genera , 182. Las genera . UFA hydreaction . Ruminocbus F2/6  can metabus F2/6 . Bacterirch diet .Fusocillus can reduce C18:1 FA to C18:0 (Butyrivibrio, which is phenotypically similar to Fusocillus can complete the BH of both C18:2 and C18:3 to C18:0 (The final step of the BH process is to convert the BH intermediates to SFAs. It was found that two bacterial species belonging to the genus to C18:0 . In addito C18:0 .Butyrivibrio group are also capable of producing stearic acid from LA and are involved in the decrease of OA (B. proteoclasticus can reduce both CLA and VA, and the two reductases used are probably different as they are not similarly affected by lactic acid (Other strains of the se of OA . OA redutic acid .in vivo and in vitro by inoculating with bacteria and measuring BH products and adding bacteria or observing the effect of dietary supplements on BH products and bacterial abundance. A previous in vivo study showed that Fibrobacteriaceae family had the highest and most significant correlation with FAs related to the BH process of C18:3 (B. fibrisolvens in the rumen of the goats and supplementation of their feed with LA increased VA and total CLA concentrations in the rumen fluid, which indicates that this bacterium is involved in the BH process in vivo (Butyrivibrio group, which includes the genera Butyrivibrio and Pseudobutyrivibrio (Several studies have also been conducted to evaluate the relationship between BH and ruminal microorganisms of C18:3 . Inocula in vivo . The othrivibrio . Additiorivibrio –194, ide2 and H2, which originate mostly from the fiber degradation activity of bacteria, protozoa, and fungi (2 accumulated in the rumen can inhibit sugar oxidation, hydrogenase activity, and VFA conversion (2, thus allowing more rapid fermentation of feed (2 produced by other microbes is referred to as interspecies H2 transfer, which usually occurs between archaea and other microbial species (Methane, a natural byproduct of ruminal fermentation, is mainly produced by archaea by utilizing COnd fungi . A previnversion . The act of feed . The cap species . Therefo2 sink, thus selectively reducing the H2 for archaea. However, only approximately 1–2% of the total H2 available can be utilized by this pathway (There is limited understanding of the effects of fats on ruminal microbiota, as well as the associated methane production. Several studies revealed that fat supplementation inhibited some ruminal microorganisms possibly due to their direct toxicity toward protozoa and archaea , 199. Ad pathway , 201. Th pathway .2 availability (2 in the rumen and compete with propionate-producing microorganisms for this substrate. This is also supported by Sun et al. (in vitro fermentation and decrease the methane as associated with the relative abundance of Methanobrevibacter decline and Methanobrevibacter is considered the predominant protozoa-associated methanogen (2 for methanogens.A mixed culture study  and a pulability . Methanon et al. , who repthanogen . Therefo2 production and inhibiting the growth of cellulolytic ruminal fungi (It has been found that the effects of oilseeds enriched with C18 PUFAs and those of the removal of fungi appeared to be widely synergistic, resulting in a final methane suppression up to 45% per unit of digestible OM, compared to intact rumen liquid incubated with the basal diet as the sole substrate . This inal fungi , 144. Moal fungi . The reacis-9trans-11 CLA, such as Bifidobacterium, Clostridium, Pseudobutyrivibrio, Lactobacillus, Propionibacterium, Eubacterium, Roseburia, Enterococcus, and Pediococcus genera.Concerning rumen physiological activity, a throughout understanding of the symbiotic relationship among microorganisms is important for predicting the response of microorganisms to C18 PUFAs. The addition of PUFAs in dairy cow diets would increase the CLA contents of milk and other dairy products, and many rumen bacterias play a key role in this pathway that isomerizes LA to 2 consumer. Consequently, dietary fat supplementation results in a decrease in the digestibility of fiber and acetate, and an increase in the propionate to acetate ratio, finally resulting in a decrease in H2 production and thereby methane emission. This means that dietary fats supplementation also can produce milk with lower greenhouse gas emissions.Additionally, the inhibitory effect of dietary fats supplements on methane emissions seems to be 2-fold. Firstly, it acts by inhibiting the activity of the methanogenic bacteria associated with limited protozoa and fungi in the rumen. Secondly, it acts as an HEven though the effect of PUFA on microorganisms have been extensively studied, the underlying mechanism remains unclear. Further studies are necessary to test the existing hypothesis regarding such an effect. Omega-3 is a type of PUFA considered beneficial to human health. It was not discussed in this review but it would be meaningful to be addressed in future studies.XS and WW: conceptualization. XS: writing—original draft preparation. YW, XM, and SL: writing—review and editing. WW: supervision. SL: funding acquisition. All authors have read and agreed to the published version of the manuscript.


The results of structural equation modeling showed that stress partially mediated the relationship between family support and sleep quality among college students . The model R2 was 36.4%. (4) Conclusions: Schools should consider implementing sleep education, and stress relief curriculum measures to improve the quality of students’ sleep, and should focus on the role that family plays during online classes. This will help students overcome the negative emotional effects of stress in the COVID-19 pandemic and improve their learning efficiency and physical and mental health.(1) Background: During the past 3 years, the COVID-19 pandemic has severely affected the normal school schedule of college students, jeopardizing their mental health, sleep quality, and interpersonal relationships. However, previous studies have focused on the dimension of social support received, and few studies have measured in depth the association of support received from family on adolescents’ physical and mental health. Therefore, this study explored the associations between family support received by Chinese college students during COVID-19 pandemic online classes, stress and sleep quality, and the mediating role of stress. (2) Methods: A cross-sectional study conducted at Chongqing Medical University recruited 712 college students through a university-wide incidental random sample using the Questionnaire Star platform. Statistical description and correlation analysis was conducted using SPSS 25.0, and structural equation modeling was constructed using AMOS 22.0 to test for mediating effects; (3) Results: The family support score of college students during the COVID-19 pandemic online course was 19.41 ± 4.62. Correlation analysis showed that sleep quality was negatively correlated with family support (r = −0.224,  On 30 January 2020, the World Health Organization (WHO) announced that COVID-19 is a “public health emergency of international concern”, which requires international coordination . AhrbergThe family is an important bridge to the healthy development and adulthood of adolescents. A review of studies showed that a low quality family environment would increase the pressure faced by teenagers, while emotional and practical support given by the family could reduce the psychological pressure ,16,17. IDuring the COVID-19 pandemic, more and more attention has been paid to the problem of students’ stress . StudiesCollege students who receive higher FS are more likely to have good SQ and lower stress.College students with less stress are prone to have better SQ.College students with higher FS have less stress, which will lead them to have better SQ.This study recruited 712 current university students from Chongqing Medical University within one week of the end of the home network teaching activities during the COVID-19 epidemic (19 September 2022 to 27 September 2022). Students had been asked to return to school to complete their studies during this period. Questionnaire data containing general demographic characteristics, reviewing psychological stress status, FS received, and SQ during the past month of online classes were collected through a school-wide convenience sampling (episodic sampling). Before participants formally filled out the questionnaire, we had a brief introduction by a trained professional to obtain the knowledge and consent of the participants. The questionnaire filling platform and the data collection and aggregation use the Questionnaire Star software. Inclusion criteria were college students in their sophomore year and above (because freshmen had just passed the college entrance exams and had not started online teaching activities during this period), and exclusion criteria were no history of major illnesses, chronic illnesses, trauma, and incomplete questionnaire responses. In total, 660 samples were included in this study.All participants were asked to provide complete questionnaire information, including gender, age, grade, height, weight , family economic status (monthly household income), permanent family location, whether they were an only child, and GPA of the previous academic year. The specific questions and option codes are displayed in FS was assessed using the Perceived Social Support Scale (PSSS) , which wThe Depression Anxiety Stress Scale 21 (DASS-21) was used to measure participants’ perceived psychological stress over the past month, and the scale is now widely used to measure the current status of depression, anxiety, and stress in children, adolescents, and older adults ,37. The The Pittsburgh Sleep Quality Index (PSQI) scale, developed by Buysse et al. at the Pittsburgh Medical Center in 1989, was translated into Chinese by Xianchen Liu et al., in 1996, and was used to assess the SQ of subjects in the last month ,39. Thert-test, one-way ANOVA, and C × 2 column χ2 test were used for one-way comparisons, and Pearson correlation analysis was used for correlation tests. Mediation effects were modeled by AMOS 22.0 software to construct SEM and validated by Bootstrap method with a set sampling number of 200. The test level was α = 0.05.SPSS 25.0 software was used for statistical analysis of the data, and normality tests were performed for the measurement data. Independent samples A total of 660 college students enrolled in Chongqing Medical University were included in this study, including 473 (71.7%) female students, 287 (43.5%), 273 (41.4%), 56 (8.5%), and 44 (6.7%) sophomores, juniors, seniors, and above, respectively. Furthermore, 444 (67.6%) had a BMI in the normal range. More than half (55.8%) of the students reported a monthly household income of less than 5000 yuan. More than half (57.4%) of the students’ families live in urban areas. The percentage of only children in the family was 30.9%. The detection rate of group stress in the sample was 19.7%, and the percentage of the sample with SQ problems was 47.3%, as shown in p < 0.05) by family income, home address, GPA in the previous semester, and whether they were only children. SQ was significantly different between genders (p < 0.05), and detailed results are presented in FS scores differed significantly (p < 0.01), positively correlated with stress , and FS was negatively correlated with stress . Other dimensional correlations are shown in The results of Pearson correlation analysis showed that SQ of college students was negatively correlated with FS , root mean squared error of approximation (RMSEA) = 0.062 (standardized to less than 0.08), standardized root mean square residual (SRMR) = 0.036 , incremental fit index (IFI) = 0.923, adjusted goodness of fit index (AGFI) = 0.906, Tucker–Lewis index (TLI) = 0.911, normative fit index (NFI) = 0.900, comparative fit index (CFI) = 0.923, goodness-of-fit index (GFI) = 0.928 (criterion is greater than 0.90), parsimony fit index (PGFI) = 0.716, adjusted normative fit index (PNFI) = 0.773 (criterion is greater than 0.50). The factor loadings of each significant variable on the corresponding latent variables were significant, indicating that the model was acceptable. The results showed that family support negatively predicted SQ  negatively predicted stress  after controlling for psychological flexibility; stress positively predicted SQ  after controlling for FS. The mediating effect prediction model was Y= −0.271X + e1; M = −0.27X + e2; and Y= −0.13X + 0.56M + e3 .Based on the correlation between FS, stress, and SQ, we hypothesized that there is a mediating effect of stress in the prediction of SQ by FS. A SEM with FS as the predictor variable (X), stress as the mediating variable (M), and SQ as the outcome variable (Y) was constructed . The modThe bias-corrected Bootstrap method was used to test the mediating effect of stress between FS and SQ, and the 95% CIs for the total, direct, and indirect effect coefficients did not contain 0, indicating that stress partially mediates the relationship between FS and SQ, with a mediating effect of −0.150. The model R2 was 36.4%. The results are displayed in In recent years the prevalence of COVID-19, the SQ, and psychological stress of college students have received much attention from society. Having good SQ and appropriate stress is the “ballast stone” for the healthy growth of adolescents. Based on the research data of college students in Chongqing Medical University, this study confirmed the effect of FS on sleep quality and stress in college students in medical universities, and explored the mediating mechanism of stress between FS and SQ. The results of this study have implications for the promotion of “Healthy China” and the improvement of physical and mental health of medical college students.p < 0.05), while there were no significant differences in gender, grade, and BMI. As the initial and most important place for individual growth, the material environment and living atmosphere of the family have an important influence on adolescents’ psychological perceptions. During home-based OL, the study and living room become classrooms, higher income families can provide better material conditions for students, and families living in urban areas have access to relatively rich social resources compared to those living in rural areas, thus showing higher scores for FS [The sample of seniors in our study is smaller in the senior year and above, mainly because students above the senior year did not participate in this survey because they were busy preparing for exams or were not in school due to the fact that they were nearing graduation and preparing to participate in further education or internship work. However, this group of students tends to show higher levels of career insecurity and experience greater work intensity later in college , so we ss for FS . Individs for FS .Our study found a negative association between FS and SQ, i.e., higher access to FS by college students was associated with better SQ. It has been argued that FS is part of social support and studies have demonstrated the significant impact of social support on SQ ,46. HoweWe also explored how FS could not only directly affect SQ problems among college students, but also indirectly moderate SQ problems by affecting stress levels. The results showed that FS was negatively related to stress, and stress and SQ were positively related. Stress partially mediated the relationship between FS and SQ. Previous studies have demonstrated the association between having higher levels of stress and poorer SQ among college students ,48. FS iAlthough distance learning and epidemic prevention measures may provide more opportunities to improve SQ, prolonged use of electronics and reduced outdoor activity by college students may affect SQ and biorhythms . During This study shows that all of our research hypotheses hold true, namely that FS can significantly influence stress levels and SQ among medical college students, and that college students with higher stress levels have worse SQ, and that we find that mediating mechanisms of stress regulation are also significantly present. This study showed that nearly half of college students reported poor SQ and roughly one in five reported stress during COVID-19 pandemic online classes. It suggests that schools, families, and individuals may need to work together to improve the SQ and mental health of college students during pandemic online classes. First, schools should pay attention to the SQ and mental health of students forced to study online at home during the pandemic by adequately scheduling study and rest time, enhancing sleep education, improving psychological support systems, and intervening to treat students with serious psychological problems in a timely manner. In addition, college students should adjust their mindset, fully participate in outdoor sports, develop regular habits of work and rest, and improve their psychological coping skills by establishing and cultivating close relationships with parents and maintaining emotional connections to maintain good mental health.Although all the hypotheses in this study were tested, this study also contains some limitations. First, this study used a cross-sectional research method, which could not determine the causal relationship between variables. Therefore, longitudinal studies should be conducted in future studies to further discuss the impact mechanisms. Second, the results of this study were based on a medical university, and due to the specificity of the medical student population, generalization of the findings to various college student populations requires further expansion of the representative sample. Third, recall measures of SQ, stress, and FS during online classes were taken within a week after starting regular classes on campus for the previous month, and this inevitably led to some recall bias. In addition, due to the special nature of students in their senior year and above, facing the pressure of further education or employment, the sample content in our study is small, so we should consider focusing on the physical and mental health problems of this group of college students in future studies.


In view of the disadvantages of polycarboxylic acid grinding aids, such as poor reinforcement effect and cumbersome synthesis process, a new type of polycarboxylic acid grinding aid was prepared to meet the requirements of multifunctional admixture for cement concrete. The polycarboxylate grinding aid (PC) was prepared using acrylic acid, sodium allyl sulfonate, and isoprenol polyoxyethylene ether (TPEG) as raw materials, and ammonium persulfate as initiator in the nitrogen atmosphere. The effect of PC and its compound with triethanolamine (TEA) and triisopropanolamine (TIPA) on cement particle size and strength, and hydration process and structures of hydrated products were investigated. Moreover, the grinding mechanism of grinding aids was also proposed. The results indicate that the PC has good performance in both grinding and high-efficiency water-reducing. The average particle diameter of cement was reduced by 3.65 μm when 0.03 wt% of PC was added as grinding aid. Moreover, a high initial fluidity of the cement paste, 290 mm, could be reached when 0.08 wt% of PC was added. The fluidity loss of cement paste after 30 min and 60 min was 265 mm and 260 mm, respectively. After PC compounding with TEA and TIPA, 4.07 μm and 4.7 μm of the average particle size of the cement can be reduced, respectively. Based on the investigations on the hydration rate of cement hydration, the phases, and the microstructures of the hardened slurry, it could be concluded that grinding aids can change the hydration process of cement and improve the morphologies and structures of hydration products without influence on the type of hydrated products. Note that the compounded grinding aids, such as PC with TEA or PC with TIPA, can more effectively enhance the early and late strength of cement. This shows excellent comprehensive performance. In this study, a new type of polycarboxylic acid grinding aid was prepared to meet the requirements of the versatility of cement concrete additives, and to simplify the synthesis process, reduce production costs, improve the grinding effect, and improve the performance of cement concrete. Currently, an environment-friendly green development system with a saved resource is increasingly attracting attention, as it is the dominant trend for industrial development. Cement, as a very basic raw material for infrastructure, consumes high energy during its production process ,2,3. NotAt present, the most widely used grinding aids are generally composed of a mixture of one or several small molecule compounds, such as alcamines, organic compounds, inorganic salts, and industrial by-products . InvestiIt is well known that a variety of chemical additives with some dedicated functions were used in cement and concrete to enhance their performance. For example, air-entraining agent for control of the air content in concrete can improve the fluidity of fresh concrete, and enhance the frost resistance, and durability . For thePolycarboxylic acid superplasticizer (PCE) is the third generation of high-performance superplasticizer developed after the ordinary superplasticizer represented by wood calcium and the high-efficiency superplasticizer represented by naphthalene . PolycarIn this paper, polycarboxylic acids with three polar groups including carboxyl, hydroxyl, and sulfonic acid structures were synthesized by the additional polymerization of unsaturated olefin derivatives containing polar functional groups. Moreover, the influence of PC and compounds with TEA and TIPA on the cement grinding, hydration process, microstructure, and strength development were discussed.Commercially available acrylic acid , Sodium Allyl Sulfonate , and Isopentenol polyether (TPEG) were from Zhejiang, China. Deionized water, Ammonium persulphate , sodium hydroxide , triethanolamine , and triisopropanolamine  were used as raw materials. The cement clinker was from Hunan, China. The natural dihydrate gypsum  and Portland cement, with a strength of 42.5 Mpa (PO.42.5), were from Hunan, China. The reference cement had a strength of 42.5 Mpa.The polycarboxylate grinding aids are regarded as water-soluble copolymers. They are composed of carboxyl groups and long side chains of polyoxyethylene ether. Hydrogen peroxide and vitamins are used as initiators. In each process, the polymerization was carried out in a reactor with a stirrer and a reflex condenser. First of all, 2.16 g (0.03 mol) of acrylic acid, 0.57 g (0.004 mol) of sodium allyl sulfonate, and 24 g (0.01 mol) of TPEG were dissolved in 30 g of deionized water and heated to 65 °C. Secondly, 0.16 g of ammonium persulfate aqueous solution was slowly added dropwise under nitrogen protection. The reaction was stirred for 3 h and held for 1 h. After cooling to room temperature, the pH of the solution was adjusted from 4 to 5 using a 1 mol/L aqueous solution of sodium hydroxide. A pale yellow transparent polycarboxylic acid was obtained with a solid content of 39.8%. The structure of the PC is shown in −1). The PC was dried in a vacuum drying oven then mixed with KBr and pressed into disks. The particle size of cement, which was prepared with 95% clinker  and 5% natural dihydrate gypsum ball milling for 25 min, was tested by laser particle sizer . The heat release rate of cement for 48 h was detected by TAM Air Microcalorimeter. Due to the water reduction of polycarboxylic acid, the cement paste fluidity was tested. The amount of polycarboxylic acid is 0.12% to 0.24%. We recorded the flow rate at 0, 30, and 60 min, respectively. Cement compressive strength was tested by the TYA-300B microcomputer controlled constant load tester to test the compressive strength for 3 days and 28 days. Cement hydration products were characterized by X-ray diffraction  and their microstructure was analyzed by SEM .The molecular structure of the polycarboxylate grinding aid was confirmed by FT-IR , and glycerin, orientate to a polar surface with the polar parts of the molecule, while the non-polar remainder shields the particle. They found that adsorption onto cement surfaces happens by coordination of Ca2+ ions and hydrogen bonds as well as other polar interactions. When the particles are very fine, the opposite charge, as mentioned above, will be agglomerated by ionic bonding. As a result, grinding efficiency will be reduced. As for the grinding aids, they could be absorbed on the surface of cement particles, neutralize the charge-screening attraction, prevent agglomeration of particles, and enhance flowability of powders, leading to an improved grinding performance. Recently, it was also shown that polymer-based grinding aids, such as polycarboxylate ethers, are very effective regarding the flowability enhancement, especially of cement powder [2+-induced surface electrostatic adsorption, and β-cyclodextrin can prevent other polycarboxylic acid molecules from approaching concrete particles, and enhance the β-cyclodextrin. Polycarboxylic acid superplasticizer inhibits the adverse effect of concrete on its dispersion performance. In the work, the grinding mechanism is proposed as shown in 2− ions from the surface of cement particles. Both TEA and TIPA could form hydrogen bonds with polar groups of polycarboxylic acid and O2− ions, building a stable three-dimensional network membrane, effectively preventing powder agglomeration, and improving the interparticle fluidity. In TIPA, the methyl, which is electron-donating, group in TIPA, and the oxygen atom in the hydroxyl group is more negative, and the hydrogen bond energy is greater than the TEA. This could be responsible for the improved grinding performance of cement with the presence of GA2 as grinding aid.TIPA has a unique three-dimensional structure and high polarity, so it can play a good dispersion role in the cement grinding process, weaken the agglomeration of powder, and have a better grinding effect . By meant powder . Moreovet powder  et al. ct powder  concludeIn general, polycarboxylate is widely used in cement and concrete as a water reducer. The influence of different amounts of the polycarboxylate grinding aid on the fluidity of cement paste is shown in 3A and C4AF by chelating with Ca2+ and Fe2+ and accelerating SO42− depletion. Moreover, the exothermic rate of hydration of GA1 and GA2, especially GA2, are higher than that of PC, which could significantly increase the early strength of cement.The polycarboxylate grinding aid, GA1, and GA2 were mixed into the Portland cement, respectively, in order to study the hydration exothermic rate curve, as shown in 3S and C2S in cements were weakened from day 3 to day 28, indicating decreased content of C3S and C2S, but increased contents of C-S-H and CH. Moreover, the hydration behavior of cement with grinding aids was consistent with cement without grinding aids. However, the aids could change the hydration and hydration product structure.2 atmosphere. By studying the effects of PC and its compound triethanolamine (TEA) and triisopropanolamine (TIPA) on cement particle size, strength, hydration process, hydration products, and cement hardening slurry structure, the grinding aid mechanism of the ternary polar polycarboxylic acid grinding aid was explored. The results of the study indicate that:In this paper, the polycarboxylic acid with polycarboxylate grinding aid was prepared using acrylic acid, sodium allyl sulfonate, and isoprenol polyoxyethylene ether (TPEG) as raw materials, and ammonium persulfate as initiator in an NThe polycarboxylate grinding aid has both good grinding aid and efficient water reducing properties, delaying the accelerated period of cement hydration and generating secondary calcium alumina, which has little effect on cement strength and structure of hydration products.The average particle diameter of cement was reduced by 3.65 μm when 0.03 wt% of PC was added as grinding aid. Moreover, high initial fluidity of the cement paste, 290 mm, could be reached when 0.08 wt% of PC was added. The fluidity loss of cement paste after 60 min and 90 min was 265 mm and 260 mm, respectively. After PC was compounded with TEA and TIPA, 4.07 μm and 4.7 μm of the average particle size of the cement can be reduced, respectively, and 5.9 MPa and 7.7 Mpa in” PO.42.5” cement in 28-day strength can be increased, respectively.Through the analysis of the cement hydration exothermic rate, hardened slurry physical phase, and microstructure, the PC can change the cement hydration process, but has no effect on the product type, and can improve the hydration product morphology and structure.The polycarboxylate grinding aid compounded with TEA and TIPA can improve cement grinding aid performance, significantly improve cement strength and increase the exothermic rate of hydration. Moreover, it leads to a secondary hydration acceleration period, which improves which improves the cement-hardening paste microstructure and contributes to the enhancement of cement.


The outbreak of COVID-19 epidemic has increased work demands for medical staff and has a certain impact on their mental health. The present study aimed to examine the role of perceived stress and social support in explaining the association between the occupational stressors and three mental health symptoms  of frontline medical staff. Five hundred twenty five frontline medical staff were investigated online after the outbreak of the COVID-19  in China. The results found that the prevalence of anxiety, depression, and insomnia among frontline medical staff were 39.8, 29.9, and 37.9%, respectively. Occupational stressors were associated with anxiety, depression, and insomnia symptoms. Perceived stress significantly mediated this link. Social support moderated the second half of the indirect effect of occupational stressors on anxiety and depression symptoms. Under the epidemic situation of COVID-19, for frontline medical staff, high perceived stress and low social support may increase vulnerability for mental health symptoms triggered by occupational stressors. Thus, improving the social support and promoting the cognitive reappraisal of perceived stress may help to maintain mental health among medical staff. The World Health Organization (WHO) has declared the outbreak of coronavirus disease 2019 (COVID-19) a pandemic. The COVID-19 virus has spread in more than 220 countries, 5.9 million people have died of COVID-19 and more than 430 million have been infected by the end of 25 February, 2022 . In addiMultiple studies have demonstrated that the elevation of work demands and the necessity to engage in greater and highly stressful work responsibilities have significant negative consequences on the mental health of frontline COVID-19 medical staff . HoweverSocial support is an essential social factor that can mitigate the negative effects of stress. Social support is associated with higher levels of positive mood, fewer health complaints, lower depressive symptoms, minimal sleep problems, and higher life satisfaction . In thisTherefore, the purpose of this study is to (a) establish associations among occupational stressors, perceived stress and mental health symptoms , (b) understand the underlying mechanisms behind these associations, and (c) demonstrate how social support can mitigate the link between occupational demands or stress and depression, anxiety, and insomnia symptoms respectively.Occupational stressors refer to social and physical work-related circumstances that challenge the adaptive capabilities and resources of an employee. Occupational stressors may trigger one’s stress response and cause psychological or physical health problems including negative emotions, sleep disturbances, and even cardiovascular disease, when one’s personal coping resources are inadequate . MedicalSince the outbreak of COVID-19, medical institutions in China and even around the world are facing unprecedented challenges. Frontline medical staff have endured months of unimaginable accumulation of work demands, compounded with their own personal obligations in this unforeseeable global disaster . Their wPsychological distress is another major adverse consequence of the COVID-19 pandemic among the medical staff. A systemic review of the mental health of 69,499 health professionals worldwide at the onset of the COVID-19 from 436 published articles found about 14–45% experienced depression, 12–36% reported anxiety, 5–33% shared having acute stress symptoms, 7–34% met criteria for post-traumatic stress disorder (PTSD), 34–36% had insomnia, and 3–43% experienced occupational burnout . These s1:H Occupational stressors is positively associated with mental health symptoms including anxiety (1a), depression (1b), and insomnia (1c).Despite the robust evidence that suggests an association between negative mental health symptoms and occupational stressors, there remains minimal understanding of how occupational stressors negatively influences mental health .The cognitive appraisal model of stress asserts that cognitive appraisal is the factor linking stressors to experienced distress, particularly, to mental and somatic symptoms. When exposed to stressors, an individual subjectively assesses the stressors  and subsequently determines which coping resources can be applied to the situation  . If the Perceived stress refers to the psychological response that an individual has after their cognitive evaluation of a stimulus as a threat. Perceived stress is one form of cognitive appraisal that may explain the link between occupational stress and mental health symptoms . EvidencFurthermore, field quasi-experiments  demonstr2:H Perceived stress mediates the association between occupational stressors and mental health symptoms including anxiety (6a), depression (6b), and insomnia (6c).While several studies have shown strong evidences for the (in)direct effect of occupational stressors on mental health symptoms via perceived stress, a few other studies have failed to find support for this pathway, suggesting these associations may be conditional on other factors.The stress-buffering model of social support provides an important perspective in understanding the potential mechanism between the occupational stressors, perceived stress, and mental health symptoms. The stress-buffering hypothesis argues that the social support protects mental health through the indirect pathway of interacting with the stressors or moderating the effect . In othePrior finding suggested that social support is not only related to objective occupational stressors, but also related to individual perceived stress . Occupat3:H Social support moderates the association between occupational stressors, perceived stress, and mental health symptoms including anxiety (3a), depression (3b), and insomnia (3c).In this context, understanding the shifts in the frontline medical staff’ mental health during the COVID-19 pandemic and the factors that may be influencing changes in mental health is relevant to comprehending frontline medical staff’ responses to the ongoing pandemic. Furthermore, few studies have investigated the potential mechanism of occupational stressors and mental health symptoms of frontline medical staff during the COVID-19 pandemic. It is important to understand the effect of perceived stress and social support on this association to effectively prevent and treat psychological distress for frontline medical staff. This may provide some intervention measures to develop public health management in the future. Taken together, the aims of the present study are to (1) estimate the prevalence of and severity of three kinds of mental health symptoms including depression, anxiety, and insomnia among frontline medical staff, (2) identify the mediating role of perceived stress in the link between the occupational stressors and three kinds of mental health symptoms respectively, and (3) evaluate the moderating role of social support in the link among occupational stressors, perceived stress and three kinds of mental health symptoms. The full proposed model is displayed in 1 a widely used online survey platform in China. According to the data on the 2020 coronavirus cases in China provided by the National Health Commission (NHC), the novel coronavirus outbreak (COVID-19) reached its peak between January 23, 2020 and February 4, 2020 and the number of new cases has steadily declined ever since. By January 29, 2020, 33,000 people had returned to Wenzhou from Wuhan and its neighboring cities, and 172 individuals were confirmed positive cases of COVID-19 in Wenzhou, making the city become the area with the most confirmed cases outside of Hubei Province in China. Lockdown was enacted in Wenzhou to curb the spread of COVID-19 virus on February 5, 2020.Participants were frontline medical staff residing in Wenzhou, China who directly participated in the fight against COVID-19 by contacting confirmed COVID-19 cases or their specimens in the isolation hospitals . This stM = 35.29, SD = 7.05 years), 442 (84.2%) at college or higher education levels, and 416 (79.2%) were reported being married. The length of professional medical service ranged from 0 (<1 year) to 44 years . Details of socio-demographic characteristics of the participants are displayed in The sample recruitment procedure consisted of a two-step procedure conducted in February 2020. First, a pilot study was conducted with the participation of 10 frontline medical staff from the target population to evaluate clarity, comprehensiveness, and acceptability of questionnaires. Second, in the formal study, links to the survey were sent to frontline medical staff via WeChat . Participants completed and submitted the questionnaire on their smartphones by clicking the survey link. The questionnaires were responded anonymously and voluntarily. An online consent form was provided to the participants before filling out the questionnaire. The survey would not continue unless participants chose the option – “Yes, I consent to take part in this survey.” Hence, a total of 525 frontline medical staff residing in Wenzhou participated. Of the 525 participants, 392 (74.7%) were female, ages ranged from 19 to 60 years-old   was utilFive items assessing participants’ perceptions of support from (1) family, (2) friends, (3) supervisors, (4) colleagues, and (5) Mental health worker during the COVID-19 epidemic were used as indicators of social support. Responses were recorded on a 4-point scale ranging from “not at all” to “extremely strong.” Example items include “I get help and support I need from my family” and “I get help and support I need from my friend.” A higher mean score indicates stronger social support. The items demonstrated good internal consistency in this sample (α = 0.86).The self-designed questions were used to measure the occupational stressors of frontline medical staff during the COVID-19 outbreak. It consists of three items: (1) work difficulty, (2) work stress, and (3) work risk during the COVID-19 pandemic. Example items include “My work was very difficult during the epidemic” and “My work was at great risk during the epidemic.” Participants were asked to score each item on a 5-point scale, from 1 (Strongly Disagree) to 5 (Strongly Agree). The higher scores the score is, the more occupational stressors. In this study, the items had acceptable an internal reliability (α = 0.77).The Generalized Anxiety Disorder Scale-7 item (GAD-7)  was usedThe level of depression in participants was assessed using the Patient Health Questionnaire-9 item (PHQ-9) . A 4-poiThe Insomnia Severity Index (ISI)  was usedThe data for this study were based on self-reports from frontline medical staff, it was possible that there could be an issue with common method variance. We used Harman’s one-factor test to detect the presence of common method bias . ResultsFirst, mean, standard deviation, and frequency of the socio-demographic characteristics of the sample were examined. We calculated prevalence estimates and frequency of the mental health symptoms among frontline medical staff during the COVID-19 epidemic. Second, for the main analysis, the descriptive information and correlation matrix were conducted. Third, after all the data were standardized, based on 5,000 bootstrap samples, the PROCESS macro  was used2 = 1013.07, df = 227, p < 0.001, comparative fit index (CFI) = 0.90, and root mean square error of approximation (RMSEA) = 0.08, in which anxiety and depression and insomnia were distinct constructs, fit the data better than a one-factor model . The result of these confirmatory factor analyses indicated the appropriateness of treating anxiety, depression, and insomnia as empirically distinct constructs.Confirmatory factor analyses were performed to discern whether the anxiety, depression, and insomnia represented the symptoms of mental health had a good fit. A three-factor model, χps < 0.05). Social support was significantly and inversely correlated with anxiety, depression, and insomnia respectively (ps < 0.001). Social support was negatively associated with perceived stress (p < 0.001), but not with occupational stressors. In addition, in demographic variables, age was positively associated with occupational stressors and anxiety respectively (ps < 0.05); length of service was positively associated with occupational stressors and anxiety respectively (ps < 0.05); education level was positively associated with occupational stressors and depression respectively (ps < 0.05); marital status was significantly and inversely correlated with occupational stressors and anxiety respectively (ps < 0.05); and sex identification did not significantly correlate with any of the variables (ps > 0.05), as such it was excluded from the remaining analysis.Descriptive statistics and correlations for some variables measured are reported in t = 6.87, p < 0.001, ΔR2 = 0.08; depression: β = 0.55, t = 5.77, p < 0.001, ΔR2 = 0.06; and insomnia: β = 0.29, t = 1.99, p < 0.05, ΔR2 = 0.0037), providing support for Hypothesis 1 a/b/c. Occupational stressors were also significantly positively associated with perceived stress . Perceived stress was significantly associated with mental health symptoms .The variable occupational stressors were significantly associated with mental health symptoms respectively   was usedIn the model of anxiety, as shown in In the model of depression, as shown in In the model of insomnia, as shown in In sum, the results supported Hypothesis 2. Specifically, perceived stress was a partial mediator of the link between occupational stressors and anxiety, depression symptoms, and was a full mediator of the link between occupational stressors and insomnia symptoms.Hypothesis 3 proposes that participants’ social support moderates the relationship between occupational stressors, perceived stress, and three mental health symptoms. Model 15 of t = −0.72, p = 0.47, ΔR2 = 0.0007), but the interaction between perceived stress and social support on anxiety was significant  after accounting for the mediating role of perceived stress. Thus, social support moderates the indirect effect of occupational stressors on anxiety via perceived stress but does not moderate the direct effect of occupational stressors on anxiety.In the model of anxiety, as shown in To clarity the direction of the interaction, the variable anxiety was plotted on perceived stress, separately at high (1 SD above the mean) and low (1 SD below the mean) levels of social support. slope = 0.40, SE = 0.04, p < 0.001). For participants with a high level of social support, the effect of perceived stress on anxiety symptom was also significant  but not as strong as that for participants with low social support.Furthermore, simple slope tests showed that participants with low level of social support (1 SD below the mean) and higher perceived stress combined were associated with more anxiety symptom ]. The indirect effect of perceived stress for participant with low social support  was stronger than those with high social support . Therefore, our hypothesis 3a was supported.t = −1.30, p = 0.19, ΔR2 = 0.002), but the interaction between perceived stress and social support on depression was significant  after accounting for the mediating role of perceived stress. This indicates that social support can moderate the indirect effect of occupational stressors on depression via perceived stress, but cannot moderate the direct effect of occupational stressors on depression.In the model of depression, as shown in To clarify the direction of the interaction, participants’ depression symptom was plotted on perceived stress, separately at high (1 SD above the mean) and low (1 SD below the mean) levels of social support. slope = 0.42, SE = 0.04, p < 0.001). For participants with a high level of social support, the effect of perceived stress on depression symptom was also significant  but not as strong as that for participants with low social support.Further, simple slope tests showed that low level of social support (1 SD below the mean), and higher perceived stress combined was associated with more depression symptom ]. The indirect effect of perceived stress for participant with low social support  was stronger than those with high social support . Therefore, our hypothesis 3b was supported.t = −0.80, p = 0.42, ΔR2 = 0.001), and the interaction between perceived stress and social support on insomnia was also not significant . Thus, Hypothesis 3c was not supported.In the model of insomnia, as shown in In sum, Hypothesis 3 was partially supported. Specifically, social support could moderate the indirect effect of occupational stressors on anxiety and depression, but not insomnia; social support cannot moderate the direct effect of occupational stressors on three mental health symptoms .As an international public health emergency, COVID-19’s impact on mental health has gained widespread attention from the public. This study estimated the prevalence and severity of three mental health symptoms among frontline medical staff. It also evaluated the mediating role of perceived stress in the link between the occupational stressors and three mental health symptoms separately. Finally, it examined the moderating role of social support in the link among occupational stressors, perceived stress, and three mental health symptoms respectively.The first finding of the study is that the prevalence of anxiety, depression and insomnia symptom among frontline medical staff were respectively 39.8, 29.9, and 37.9%. Although these incidence rates are within the estimated range of mental health symptom reported in the global studies of frontline medical staff , it is aThe second finding of the study is that occupational stressors were positively associated with three mental health symptoms including anxiety, depression, and insomnia. These findings are in line with the first hypothesis and consistent with recent studies regarding the relationship between occupational stressors and mental distress . Extra wThe third finding of the study is that perceived stress was a strong statistical mediator of the relationship between occupational stressors and three mental health symptoms among frontline medical staff. It supports the second hypothesis and is consistent with results of previous stress studies . This meImportantly, we found that perceived stress was a partial mediator of the link between occupational stressors and anxiety and depression among frontline medical staff. The cognitive appraisal theory shows that psychological distress is not solely the results of stressful events, but is also determined, to a large extent, by individual cognitive evaluation . The medFurthermore, perceived stress was a full mediator and not a partial mediator of the link between occupational stressors and insomnia among frontline medical staff. This result indicated that the direct effect of occupational stressors on insomnia is weak, and the occupational stressors influences the insomnia mostly through the mediation role of perceived stress. Thus, to the extent possible, sustainable strategies may be developed and implemented to reduce perceived stress among frontline medical staff. A recent randomized controlled trial (RCT) found that a mindfulness-based stress reduction program was effective in reducing perceived stress among breast cancer survivors in China . Future The fourth finding of the study is that social support did not moderate the direct effects of occupational stressors and three mental health symptoms, but moderate the indirect effects of occupational stressors on anxiety and depression (not insomnia) via perceived stress. The results revealed that higher perceived stress was associated with more anxious and depressive emotional reactions in individuals with low social support. This is consistent with the buffer theory of social support, stating that low social support may be one of the main reasons why individuals suffering from the heavy and acute occupational stressors tend to experience negative emotions such as anxiety and depression .Moreover, this study extends this view in three ways. First, social support can provide a buffer for individuals’ negative emotional reactions when dealing with occupational stressors. This buffer is legitimately not evident for medical staff somatic symptoms such as insomnia: COVID-19 leads to realistically enormous physical constraints including intermittent or irregular sleep hygiene in medical staff and these can limitedly be alleviated through social support. In addition, even without the pandemic, the prevalence of sleep disturbances among medical staff is still higher than general population . Thus, wSeveral limitations in this study should be mentioned. First, the respondents were all from Wenzhou, Zhejiang Province, which is one of the worst COVID-19 affected cities in China except Hubei Province. Certainly, the findings pertain may not generalize to frontline medical staff in other regions of China. Second, our study was based on cross-sectional design and causal inferences was limited. Future studies may adopt a longitudinal research design to provide evidence for the causal assumptions reported in this study. Thirdly, this study did not explore the potential relationship between demographic variables  and mental health symptoms. In the future research, we will focus on it. Finally, we used a self-designed questionnaire to measure occupational stressors, and the results of the study relied on self-reported data, which may be subjective to some extent. Future research should choose standardized questionnaires whenever possible and collect data from multiple informants  or multiple methods .Despite the aforementioned limitations, our study has meaningful implications in medical practice. First, based on the findings of high prevalence of anxiety, depression, and insomnia among frontline medical staff during the COVID-19 epidemic, the Chinese hospital managers may attend more to the growing concern of mental health among medical staff by increasing mental health awareness training, establishing mental health risk assessment, and empowering efficient coping interventions. Second, there is a significant association between occupational stressors and mental health symptoms among the frontline medical staff. Continuing medical education and targeted training in biological disaster ability can reduce occupational stressors, and thus improve the mental health of the medical staff. Organizational training on adequate work-related climate to navigate crisis interventions may also accentuate structurally-driven occupational stressors. Third, perceived stress is an important mechanism by which the occupational stressors of unexpected public crisis affect mental health among frontline medical staff. At the organizational level, the provision of adequate facilities, supportive health climate, inclusive work culture, along with wellbeing incentives, and can help medical staff to reduce their perceived stress . At the The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding authors.The studies involving human participants were reviewed and approved by the Ethics Committee of the Wenzhou Medical University. The patients/participants provided their written informed consent to participate in this study. Written informed consent was obtained from the individual(s) for the publication of any potentially identifiable images or data included in this article.DB, LC, YLi, YZ, YLu, and FZ participated in research design. DB, LC, XL, AN-A, KX, LH, HW, and ZC collected the data. DB, LC, YLi, YZ, YLu, and GS conducted the data analysis. DB, LC, YLi, YZ, YLu, FZ, XL, and AN-A wrote and contributed to the writing of the manuscript. All authors have read and agreed to the published version of the manuscript.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.


Mean muscular area rectus anterior (MARA) was 4.09 ± 1.5 cm2, and mean muscular circumference rectus was 8.86 ± 1.61 cm. A positive correlation was observed between the MARA and fat-free mass index (FFMI) determined by anthropometry , BIA , and DXA , as well as muscle function  and respiratory parameters . A total of 25 patients (52.1%) were diagnosed with malnutrition according to GLIM criteria. Differences were observed when comparing the MARA based on the diagnosis of malnutrition . Conclusions: In adults with cystic fibrosis, the measurements collected by muscle ultrasound of the QRF correlate adequately with body composition techniques such as anthropometry, BIA, DXA, and handgrip strength. Muscle ultrasound measurements, particularly the MARA, are related to the nutritional status and respiratory function of these patients.Background: Muscle ultrasonography of the quadriceps rectus femoris (QRF) is a technique on the rise in the assessment of muscle mass in application of nutritional assessment. The aim of the present study is to assess the usefulness of muscle ultrasonography in patients with cystic fibrosis, comparing the results with other body composition techniques such as anthropometry, bioelectrical impedance analysis (BIA), dual-energy X-ray absorptiometry (DXA), and handgrip strength (HGS). At the same time, we intend to assess the possible association with the nutritional and respiratory status. Methods: This was a prospective observational study in adult patients with cystic fibrosis in a clinically stable situation. Muscle ultrasonography of the QRF was performed, and the results were compared with other measures of body composition: anthropometry, BIA, and DXA. HGS was used to assess muscle function. Respiratory parameters were collected, and nutritional status was assessed using Global Leadership Initiative on Malnutrition (GLIM) criteria. Results: A total of 48 patients were included, with a mean age of 34.1 ± 8.8 years. In total, 24 patients were men, and 24 patients were women. Mean BMI was 22.5 ± 3.8 kg/m Cystic fibrosis (CF) is a disease caused by the alteration of a single gene located on the long arm of chromosome 7—the CFTR gene (regulator of the transmembrane conductance of cystic fibrosis). It consists of a multisystemic disease in which CFTR protein dysfunction causes alteration of ion transport in the apical membrane of epithelial cells in different organs and tissues. It is the most frequent life-threatening disease, with recessive Mendelian inheritance, in the Caucasian population .Until a few years ago, CF was considered to be associated with malnutrition because it was practically always present at the time of diagnosis, and because the vast majority of patients suffered a deterioration in their nutritional status and died severely malnourished. Currently, the prevalence of malnutrition has decreased notably, although figures close to 25% continue to be reported in both children and adults . Pseudomonas), which is accentuated with age. This is why nutritional intervention can, in addition to improving nutritional parameters, slow down the progressive decline in lung function.Malnutrition affects the respiratory muscles and, thus, lung function, decreases exercise tolerance, and leads to immunological alteration. In both children and adults, it behaves as a predictive risk factor for morbidity and mortality and deterioration in quality of life ,5,6,7,8.Although, until recently, the recommendations focused mainly on achieving adequate weight, height, and body mass index (BMI) , the neeTherefore, in patients with cystic fibrosis, it is recommended to collect body composition measurements ,12. To dIn our series of adults with cystic fibrosis, we have been carrying out some of these body composition assessment techniques. Using BIA, 16.2% of our patients presented a low fat-free mass, compared to 17.7% using anthropometry and increasing to 37.6% using DXA . In 2018, Global Leadership Initiative on Malnutrition (GLIM) criteria . This teTaking into consideration the above, the diagnosis and prevention of malnutrition are essential in patients with CF, paying special attention to muscular body composition, for which a simple, accessible, and reliable method is needed that can be performed as a routine analysis in consultation, such as muscle ultrasound of the QRF .Our hypothesis is that muscle ultrasonography could be an appropriate technique for measuring muscle mass in the nutritional assessment of patients with cystic fibrosis, and that it would have good agreement with other diagnostic tools for estimating muscle mass and strength.Thus, the aim of the study was to assess the usefulness of muscle ultrasonography in the diagnosis of malnutrition in patients with cystic fibrosis, comparing the results with other body composition techniques such as anthropometry, handgrip strength, BIA, and DXA. At the same time, we intend to assess the possible association with the nutritional and respiratory status during patient follow-up.We designed a prospective observational study of routine clinical practice. Adult patients with a diagnosis of cystic fibrosis in a situation of clinical stability assessed at the Nutrition Unit of the UGC of Endocrinology and Nutrition of the Hospital Regional Universitario de Malaga were selected, coinciding with the annual study that is usually carried out.Weight was assessed through BIA  and height was obtained using a stadiometer . With these two values, BMI was calculated. BIA was performed with TANITA MC980MA , providing information about total body composition (phase angle and fat-free mass).Dual-energy X-ray absorptiometry (DXA) was performed using a Lunar Prodigy Advance densitometer . Fat-free mass was recorded. The software used was EnCore 12.3 (iDXA and Prodigy Advance). The skinfolds assessed were the triceps, biceps, subscapularis, and supra-iliac using a Holtain constant pressure caliper . The same investigator (N.P.) performed the measurements in triplicate for each of the skinfolds assessed, and the mean was calculated. Fat mass and fat-free mass (FFM) were estimated according to the formulas of Siri and Durnin ,29. Age,The fat-free mass index (FFMI) was calculated for anthropometry, BIA, and DXA.Muscle strength was assessed using a Jamar dynamometer  and was performed in the dominant hand, repeated three times. The mean was calculated.X- and Y-axis (transverse muscle thickness), circumference (CMR), cross-sectional area (MARA), and transverse subcutaneous adipose tissue (cm) (SCAT) [2/m2) (MARAI) was calculated. The ultrasonography was performed by the same person (G.O.) who was familiar with the technique. Three measurements were performed for each parameter, and the mean was calculated. Muscle ultrasonography of the QRF was performed on the nondominant lower extremity with the patient in a supine position, using a 10–12 MHz probe and a multifrequency linear matrix color Esaote MyLab Gamma . The probe was aligned perpendicular to the longitudinal and transverse axis of the nondominant QRF. The evaluation was performed without compression at the level of the lower third from the superior pole of the patella and the anterior superior iliac spine, measuring the ) (SCAT) . The ind2), or a decrease in muscle mass determined by DXA (gold standard). Regarding etiological criteria, reduced intake and reduced assimilation were assessed, especially the existence of pancreatic insufficiency. Lastly, chronic disease-related inflammation was assessed using the Glasgow Prognostic Score [A nutritional assessment was performed according to GLIM criteria. For achieving a diagnosis of malnutrition, the presence of at least one phenotypic criterion and one etiologic criterion was required . The folic Score .®, Erich Jaeger, Würzberg, Germany), following the Sociedad Española de Neumología y Cirugía Torácica (SEPAR) guidelines and determining the values of forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1), and the ratio between both (FEV1/FVC). The values were expressed in absolute terms in mL and as percentages according to a reference population [The exacerbations recorded during the annual examination were assessed, taking into consideration those happening in the year prior to the evaluation. Such exacerbations were classified into mild/moderate or severe . Moreover, patients underwent forced spirometry using a JAEGER pneumotachograph . The associations of the variables were evaluated by estimating the Pearson or Spearman correlation coefficient, according to normality. For calculations, significance was set at p < 0.05 for two tails.Quantitative variables were expressed as the mean ± standard deviation. The distribution of quantitative variables was assessed using the Kolmogorov–Smirnov test. Differences between quantitative variables were analyzed using Student’s Evaluations of the diagnostic performance of muscle ultrasound variables to detect malnutrition according to GLIM criteria were based on the receiver operating characteristic (ROC) curves and the area under the curve (AUC). We estimated the accuracy of these measurements using AUC by plotting sensitivity versus 1 − specifity. ROC curves were used to determine the optimal cutoff values by finding the point maximizing the product of sensitivity and specificity. Data analysis was performed using the JAMOVI software . All subjects gave their informed consent for inclusion before they participated in the study. The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Research Ethics Committee of Malaga on 30 March 2021 (reference number #30032021).A total of 48 patients were included. They had a mean age of 34.1 ± 8.8 years. Of the sample, a total of 24 were men (50%) and 24 were women (50%). Half of the individuals were heterozygous for ΔF508, and 77% had pancreatic insufficiency. Furthermore, 18 patients (37.5%) presented disease-related inflammation (Glasgow prognostic score > 0).2). In the application of the GLIM criteria for the diagnosis of malnutrition, we found that seven patients (14.5%) had lost more than 5% of their weight in the previous 6 months, and 13 patients (27%) had a BMI below 20 kg/m2.According to the BMI, only 8.3% of women and 12.5% of men had malnutrition  had an FFMI below the cutoff points (61.1% of women and 23.5% of men). With these data, 25 patients (52.1%) were diagnosed with malnutrition according to GLIM criteria (64% of women and 36% of men).The correlation between the muscle ultrasonography measurements and BMI, although statistically significant, was weak.r = 0.747; p < 0.001, r = 0.736; p < 0.001, A statistically significant correlation was found between the fat-free mass determined by anthropometry and the muscle ultrasound variables, highlighting a good correlation with the muscular area rectus anterior (MARA)   and Y-axis .A comparison between muscle ultrasound parameters according to the nutritional status of the patient is shown in 2, with AUC = 0.664 (sensitivity 72.7% and specificity 69.2%), in women and 4.71 cm2, with AUC = 0.732 (sensitivity 68.8% and specificity 85.7%), in men. Using the ROC curve, we determined the MARA cutoff points for predicting malnutrition . ROC curTo our knowledge, this is the first study to include the assessment of muscle ultrasonography of QRF in adult patients with cystic fibrosis. We found that muscle ultrasonography correlates with handgrip strength and body composition measurement techniques such as BIA, DXA, and anthropometry in patients with cystic fibrosis. In turn, we found an association between this tool and nutritional status and respiratory parameters.Malnutrition and muscle mass depletion are related to an increase in complications and a worse prognosis in patients with cystic fibrosis. To assess the nutritional status of patients with cystic fibrosis, it is necessary to perform measurements of body composition beyond BMI. We used muscle ultrasonography to assess body composition as it is a simple, accessible technique, and free of radiation. Our study found a good correlation between muscle ultrasound measurements and the remaining morphofunctional assessment techniques, consolidating the results of previous studies . As expePrevious studies found that the prevalence of low FFM is high in adult CF patients, despite a normal BMI . In our However, muscle ultrasound measurements did show a good correlation with fat-free mass, using both BIA and anthropometry. The ultrasound parameters that best correlated with estimated FFM were MARA and muscle circumference. On the other hand, an association was also found between ultrasound and phase angle, a biomarker for malnutrition, hydration, and inflammatory status . Muscle Although DXA is considered the “gold standard” in the clinic for estimating fat-free mass, the ultrasound parameters showed slightly lower correlations than those observed with the other techniques. Other previous works have pointed out differences in the estimation of fat-free mass between DXA and BIA and anthropometry in patients with CF , findingHandgrip strength is a muscle assessment technique that is a good functional and global health status marker. It is a good marker of renutrition , and it Y-axis) and respiratory function parameters. Even without being able to establish causal relationships, patients with lower muscle mass determined by ultrasound seemed to have worse FEV1, FVC, and FEV1/FVC values. This finding was previously described in patients with low muscle strength [In our study, we found an association between muscle ultrasound parameters (especially the MARA and strength ,45 or postrength ,15,40,46Y-axis. In previous studies, it was reported that malnourished patients with CF presented worse handgrip strength values [To our knowledge, this is the first study to show the prevalence of malnutrition in adult patients with CF applying the GLIM criteria. Malnourished patients presented worse muscle ultrasound values, again best represented on the MARA and h values . Regardih values , where mh values . TherefoThis study had some limitations. It was a cross-sectional study, which prevented us from extracting causal conclusions; thus, we could only speculate on different associations. Moreover, it was a single-center study on a moderate number of participants. On the other hand, the muscle ultrasound measurement technique is not yet universally accepted, as nutritional ultrasound is considered to be a developing technique, lacking population reference values and widespread cutoff points .Nonetheless, as strengths of our study, we highlight that all measurements were performed by a single, experienced observer using standardized methodology . FurtherY-axis, are related to the nutritional status and respiratory function of these patients. It is a simple, accessible, reliable, low-cost, and noninvasive technique that could be used to assess the muscle mass of these patients, helping to diagnose malnutrition and monitor the evolution in patients with CF. However, further studies are required to provide information on normal values and widespread cutoff points.In conclusion, in adults with cystic fibrosis, the measurements collected by muscle ultrasonography of the quadriceps rectus femoris correlate adequately with body composition techniques such as anthropometry, BIA, DXA, and handgrip strength. Muscle ultrasound measurements, particularly the MARA and


Pericarpium Citri Reticulatae (PCR) is a natural citrus by-product with beneficial health and nutritive properties that is used widely in food and is an ingredient in traditional Chinese medicine. PCR improves gradually with aging. However, the present research has not yet revealed the reasons for this. Some data prove the important role of microorganisms in the quality of tobacco and fermented tea with the time of the aging of these foods. Our studies further proved that the coexisting Aspergillus niger plays an important role in the change of flavonoids and volatile oil in PCR during this process. Therefore, we put forward that longer storage is better for PCR and is highly correlated with the change of the coexisting microbial population structure caused by environmental factors. Samples of PCR aged in Beijing, Sichuan, Guangdong, and Yunnan were collected at different time points. Using GC/MS and high throughput 16S rDNA and ITS sequencing techniques, massive changes in volatile profile and microbial communities were observed during aging. Spearman correlation analysis indicated that Exobasidium, Xeromyces, Pseudocercospora, Russula, Aspergillus, Herbaspirillum, Sphingomonas, and Streptococcus, which are the dominant microbial genera in Sichuan and Guangdong showed strong connections with volatile components of chemical markers. It was preliminarily verified that the changes of volatile components for PCR are highly correlated with the change of the coexisting microbial population structure caused by environmental factors, providing a new idea for the research on the aging mechanism of PCR and key influencing factors of aging quality. Citrus reticulata Blanco, and its cultivated varieties. These peels are prepared typically from freshly picked fruits that are permitted to dry in the sun or at low temperatures. PCR is a staple in foods and drugs due to its effectiveness in regulating the qi (energy), normalizing the functions of the spleen and stomach, and resolving the phlegm. To quote Tao Hongjing  between volatile components and the change of the coexisting microbial population structure caused by environmental factors is essential to understanding the underlying processes of the improvement of PCR with the time of its storage and the microbiota that drives this.Microorganisms play an important role in the aging quality formation of tobacco and fermented tea. The main cause of the formation of flavor substances is the change in the coexisting microbial population structure and metabolic enzyme, storage temperature and humidity, time, and variations of components  and bacterial 16S rDNA V4 was performed to compare the microbial community structure. The GC/MS method was applied to the analysis of main differential components. Furthermore, we applied stoichiometry and other analysis methods to analyze the correlation of microbial-volatile components. The study provides a new idea for the research on the aging mechanism of Citrus reticulata “Chachi” and lays a foundation for recommendations for PCR storage, maintenance, and quality evaluation.In this study, Citrus reticulata “Chachi” by Professor Yan Zhuyun from the Department of Traditional Chinese Medicine, College of Pharmacy, Chengdu University of Traditional Chinese Medicine. A linen bag containing the orange peels was placed in the cool, dry, and ventilated warehouse within the 302 Hospital of people's liberation army, No. 100, Middle West Fourth Ring Road, Fengtai District, Beijing City; the pharmacy building of the Chengdu University of Traditional Chinese Medicine, Wenjiang District, Chengdu City, Sichuan Province; No. 208, Didong Road, Pengjiang District, Jiangmen City, Guangdong Province; the Yunnan University of Traditional Chinese Medicine, Chenggong District, Kunming City, Yunnan Province. This allowed the product to age naturally. The same number of samples were removed from the linen bag every 3 months of storage in Sichuan and Guangdong, and every 6 months in Beijing and Yunnan. Samples were stored at −20°C before analysis of volatile compounds and were deposited at −80°C before DNA extraction. The details of the samples are shown in To ensure that the collected PCR samples were representative and uniform, all specimens were collected in early January 2020 from the fresh oranges stored for peeling in Xinmadan Village, Sanjiang Town, Xinhui District, Jiangmen City, and Guangdong Province, China. After peeling, the product was processed and dried traditionally. Specifically, the orange peels were placed under different environmental conditions like wind, sun, and natural loss of water. The drying process included the following steps: soft texture after turning the peel, turning the peel then and finishing the process by drying it. The samples were identified as The environmental factors (temperature and humidity) in the aging process of the dried orange peel were recorded by a DS 1923 button  type temperature-humidity recorder. All these parameters are shown in ® High-Fidelity PCR Master Mix with GC Buffer, and a high-efficiency high-fidelity enzyme. The V4 regions of the bacterial 16S rRNA gene and the internal transcribed spacer (ITS1) regions of fungal rRNA genes were amplified using the primers 515F (5′-GTGCCAGCMGCCGCGGTAA-3′)/806R (5′-GGACTACHVGGGTWTCTAAT-3′) and ITS1-1F-F (5′-CTTGGTCATTTAGAGGAAGTAA-3′) /ITS1-1F-R (5′-GCTGCGTTCTTCATCGATGC-3′) with barcodes, respectively , 0.25 μm. The oven temperature was programmed as follows: the initial column temperature was 60°C, with 2°C /min rise to 82°C, then 20°C /min rise to 144°C (to keep 3 min), 8°C /min rise to 260°C (to keep 10 min). The carrier gas He was in the constant current mode, the flow rate was 1.0 ml/min, the split ratio was 10:1, and the autosampler was 1.0 μl. The ion source was electrospray (EI), the ionization energy injector temperature was 270°C, the transmission line temperature was 240°C, and the solvent delay was 9 min.The barcode sequences and PCR amplification primer sequences were removed from each data file. Reads from each sample were spliced using the FLASH v1.2.7 software. The spliced sequences obtained were the raw tags. These files were filtered to obtain the clean tags  diversity plot and the Chao index. The goods coverage indices and the unweighted pair-group method were assessed by the arithmetic means (UPGMA) and were used to construct the UPGMA sample clustering tree. The R software (V2.15.3) was used to draw the petal diagram and non-metric multidimensional scale (NMDS). Volatile components were identified by the NIST MS Search Program (version 2.0g). The similarity of volatile compounds was detected in over 80% of the standard spectra library. The relative percentage content of each component was calculated by the area normalization method. SIMCA-P 14.0  was used to perform principal component analysis (PCA) together with the orthogonal partial least squares discriminant analysis (OPLS-DA), and the differential chemical markers were estimated by using variable importance in projection (VIP) values. Spearman's correlation was used to conduct analyses of volatiles and microorganisms. The experiment was carried out in three technical replicates to ensure the reliability of the data.Total fungal tags 1 115 554 with an average of 85 812 tags per sample, and 1 077 293 bacterial tags with an average of 82 869 tags per sample using the tags quality control process of the Qiime (v1.7.0) software were performed. Sequences were grouped into 5 776 OTUs for fungi and 26 047 OTUs for bacteria (both at 97% similarity level), as shown in p > 0.05), while the Ace and Chao ones had statistical differences (p < 0.05) with larger values indicating greater abundance. The combined data revealed an increase in the abundance and number of distinct fungal species on the surface of the PCR in its samples stored for 9 months of aging, where the temperature and humidity underwent a gradual increase. The combined data revealed an increase in the abundance and number of distinct bacterial species on the surface of the PCR in the 6 and 9 months of aging, with the temperature, and humidity undergoing a gradual increase  and Basidiomycota (21.85%), with smaller populations of Glomeromycota, Rozellomycota, Mortierellomycota, Chytridiomycota, Mucoromycota, Blastocladiomycota, Basidiobolomycota, and Olpidiomycota, among others , Cyanobacteria (38.59%), Firmicutes (6.65%), Bacteroidota (2.1%), Actinobacteriota (1.89%), Acidobacteriota (0.99%), Planctomycetes (0.24%), Verrucomicrobiota (0.18%), and Gemmatimonadota (0.07%)  .Lactobacillus were predominant in fresh citrus skin, while the genus Pseudomonas and Lactobacillus were abundantly distributed in SC1. Methylobacterium was predominant in GD1. Bryobacter and Terriglobus were predominant in BJ2. Paenibacillus and Lysinibacillus gathered more when samples were stored for SC2. Mesorhizobium and Ralstonia were predominant in GD2. Ralstonia was predominant in YN2. Bacillus and Sphingomonas were found in SC3, while Delftia, Streptococcus, Vibrio, and Sphingomonas gathered more when samples were stored for GD3. Alistipes, Acinetobacter, and Pseudocercospora were found in BJ4. Staphylococcus and Prevotella were predominant in SC4. Lautropia and Hydrogenophilus were predominant in GD4, while Herbaspirillum gathered more when samples were stored for YN4. Interestingly, Methylobacterium, Sphingomonas, Bacillus, and Pseudomonas accelerated the biotransformation of volatile oil in PCR. Methylobacterium, Sphingomonas, Bacillus, and Pseudomonas were dominant bacterial genera on the surface of PCR aged in Sichuan and Guangdong areas, indicating that Sichuan and Guangdong areas were suitable for natural aging of PCR.According to the results in To evaluate the similarities and differences between these samples, we carried out an MNDS analysis. The obtained results are shown in To compare volatile components of PCR samples at different stages, the chemical profiling of volatile components was analyzed by GC/MS. Steam distillation for volatile oil of PCR was prepared according to the method below 1.3, and GC/MS analysis was performed according to the method described in Section Materials and Methods. The total ion chromatogram  Benzoate and a-Sinensal reached the highest peaks in fresh peels. The relative contents of alpha-Pinene reached the highest values in GD1. The relative content of 5-isopropyl-2-methylphenol changed little while the relative content of beta-Myrcene and D-Limonene reached the highest in GD3.Exobasidium, Zasmidium, Xeromyces, Pseudocercospora, Russula, and Aspergillus were strongly correlated with chemical markers. Among them, Aspergillus was strongly correlated with most of the selected chemical markers. In detail, it was positively correlated with beta-Myrcene and D-Limonene and negatively correlated with Terpinen-4-ol, alpha-Terpineol, Thymol, 5-Isopropyl-2-methylphenol, and Methyl 2-(methylamino)benzoate. Aspergillus, especially Aspergillus niger, played an important role in the change of flavonoids and volatile oil in PCR. Data show that bio-augmented fermentation with A. niger NCUF413 was proven to enhance the liquor yield and improve the flavor of the liquor samples benzoate and a-Sinensal. Lactococcus was positively correlated with Terpinen-4-ol, alpha-Terpineol, Thymol, and 5-Isopropyl-2-methylphenol. Sphingomonas, as the dominant microbial genera of tobacco, was also proven to increase tobacco aroma. In our case, Sphingomonas and Lactococcus accelerated the biotransformation of volatile oil in PCR.Spearman analysis was used to analyze the correlation between the relative abundance of the top 35 microbial genera and the PCR chemical markers. Results are shown in Aging of PCR is very important to improve its quality. However, the natural aging process of PCR takes a long time and costs a lot. At present, the use of microbial transformation to increase active components and improve quality is widely studied. Therefore, after clarifying the correlation between volatile contents and microbial population of PCR, we can explore whether there is a method of “the artificial aging technology” to shorten the aging time, reduce economic loss, and waste of resources will be useful. In addition, microbial diversity is abundant, and their growth, physiological and biochemical characteristics will be unstable with the change in the environment. Pericarpium Citri Reticulatae can provide nitrogen and carbon sources for microbial respiration, PH alteration caused by the acid-producing microbes also affects microbial growth. Further exploring the microbial succession and its relative environmental factors could provide valuable information for understanding the mechanism of Pericarpium Citri Reticulatae aging process.Citrus reticulata “Chachi” with different aging times was consistent in composition and structure but the dominant microorganisms on its surface were different significantly. GC/MS was applied to the analysis of volatile components, and 55 volatile compounds were detected. SC3, GD3, SC4, and GD4 were distant from those representing the other samples, alpha-pinene, beta-myrcene, D-Limonene, and other 10 chemical markers were significantly different from other samples. This indicated that volatile components' relative contents were similar in areas with similar environmental factors. We further proved that Exobasidium, Xeromyces, Pseudocercospora, Russula, Aspergillus, Herbaspirillum, Sphingomonas, and Streptococcus were the dominant microbial genera in Sichuan and Guangdong, and their abundance further showed strong connections with volatile components of chemical markers. Our results allow us to highlight the key influencing factors of its aging quality. To further clarify their exact contribution, using pure strains of these microorganisms to perform fermentation, is required to validate their applications.In this study, the microbial population structure and volatile components of the 1-year aging process of PCR from Beijing, Sichuan, Guangdong, and Yunnan were analyzed. The microbial population structure in The authors acknowledge that the data presented in this study must be deposited and made publicly available in an acceptable repository, prior to publication. Frontiers cannot accept a article that does not adhere to our open data policies.FY wrote the manuscript. LH and MS analyzed data. FW modified the details. HC and YL conceived of or designed the study. All authors agreed on the contents of the paper.This research was supported by grants from the National Natural Science Foundation of China (No.81973436).The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.