Characterisation of Protein Degradation in Cheddar Cheese

Considerable research attention over the last few years has highlighted the important role of protein degradation in cheese, and its pivotal role in flavour and texture development. While possible degradation pathways of the respective protein molecules involved have been determined, many such studies have been performed using model systems, which attempt to mimic the conditions present within a maturing cheese curd. The main aims of this study were however directed at identifying how such protein degradation pathways varied in Cheddar cheese manufactured under different processing variables. The concentration of free amino acids, released through the combined action of rennet and microbial proteinase and peptidase enzymes, was found to show a marked heat treatment and pH dependent effect. Qualitative analysis of the reversed phase chromatographic profiles of water-soluble peptides from Cheddar cheese manufactured from standard pH and reduced pH milk revealed peptide differences. Further, statistical analysis of the data suggested that the observed variations in the individual amino acid concentrations from the Cheddar cheese were closely associated with differences in the peptide precursor supply. Therefore, controlling the extent and type of peptides released may help eliminate flavour defects, such as bitterness, and lead to the identification of key peptides necessary to produce Cheddar cheese of good quality. Characterisation of Cheddar cheese peptides was performed on a matrix-assisted laser desorption ionisation time-of-flight mass spectrometer, using a volatile degradation reagent, trifluoroethylisothiocyanate. Of the peptides identified, the majority came from alphas1- and beta-caseins, and mainly from their N and C-termini respectively. This result, whilst already well documented, reinforces the important requirement of identifying key peptides, if the final acceptability of a young cheese is to be predicted with certainty. Quantitative analysis of the caseins and their degradation products was achieved by the application of capillary electrophoresis. The approach highlighted significant differences in the hydrolysis of the alphas1-casein and alphas1-I-polypeptide f(24-199) between Cheddar cheese manufactured from standard and reduced pH milk