<sod >Shares in Premier Foods, the maker of Bisto, plunged 16 per cent after it warned that its full-year profit will be 10 per cent lower than previously expected, as a result of lower trade and rising food inflation costs.< eod>< sod > Shares in Premier Foods, the maker of Bisto, ended the session almost 11Â per cent lowerÂ after it warned that its full-year profit will be 10 per cent lower than previously expected, as a result of lower trade and rising food inflation costs.< eod>