PREPARATIVE METHODS OF ISOLATING BITTER PEPTIDES FROM CHEDDAR CHEESE

A preparative procedure including water extraction, membrane ultrafilt ration, and reversed-phase HPLC separation to isolate bitter peptides in Cheddar cheese was developed. The most bitter fractions in cheese s amples were in a molecular weight range of either between 500 and 3000 or >3000. When equal amounts of the lyophilized bitter fraction were incorporated back into cheese, reduced-fat Cheddar cheese samples had a more pronounced increase in bitterness intensity than full-fat chees e samples. Sensory evaluation on the eluants of preparative HPLC revea led that bitterness was found in various places along the separation, although eluants in the early region of chromatograms were generally m ore bitter. Most of the isolated bitter peptides contained a high leve l of hydrophilic amino acid residues such as glutamic acid/glutamine a nd serine. Hydrophobic amino acid residues, such as leucine, isoleucin e, and proline, were high in some bitter peptide fractions, but phenyl alanine and tyrosine were absent in all isolated bitter peptides.