Proteolysis in the Irish farmhouse blue cheese, Chetwynd

Chetwynd blue is an Irish farmhouse cheese produced from pasteurised, homogenised cows' milk. Proteolysis in two samples of this cheese was studied over a 71-day ripening period. The concentrations of pH 4.6-, trichloroacetic acid-and phosphotungstic acid-soluble N increased substantially during ripening, especially after 15 days, concomitant with mould growth and sporulation. The pH of the cheese increased from ∼4.8 at day 1 to ∼5.9 by day 71. High concentrations of amino acids had accumulated by the end of ripening, particularly glutamic acid, leucine, valine and lysine. Urea-polyacrylamide gel electrophoresis of the cheeses showed that considerable degradation of the major caseins had occurred at the end of ripening. During the early stages of ripening, proteolysis was due mainly to chymosin (rennet) but during the later stages, the fungal endo-and exo-peptidases became dominant and the cheese proteins were hydrolysed extensively. Reverse-phase HPLC showed an increase in the total concentration of pH 4.6-soluble peptides during ripening. Chromatograms of the ethanol-soluble fraction were similar to those of the pH 4.6-soluble fraction.