Abstract Pepstatin A, an inhibitor of acid proteases, was added (7.5, 15 or 30 μ mol L -1 ) to the curds/whey mixture at the start of cooking to inhibit residual coagulant in miniature (20 g) Cheddar-type cheeses. No degradation of α s1 -casein was observed by urea–polyacryl amide gel electrophoresis (PAGE) in the pepstatin-treated cheeses, indicating that all the concentrations of pepstatin used in this study effectively inhibited residual coagulant throughout ripening. The level of water-soluble N (WSN) as % of total N increased very slowly in the pepstatin-treated cheeses, while there was a steady increase in WSN in the control cheeses; after 4 months of ripening, the level of WSN in the control cheese was nearly three times as high as in the cheese treated with 30 μ mol L -1 pepstatin. Urea–PAGE of water-soluble fractions (WSF) showed marked differences between pepstatin-treated cheeses and their respective controls throughout ripening. Reverse-phase HPLC of the WSF of the cheeses showed that the peptides α s1 -CN f1-9/13, which are formed from the chymosin-produced peptide, α s1 -CN f1-23, by the action of the cell envelope-associated proteinase of Lactococcus , were not present in pepstatin-treated cheeses. Levels of total free amino acids (as determined by the Cd–ninhydrin method) were higher in controls than in pepstatin-treated cheeses throughout ripening. The results of this study demonstrated that pepstatin is a very effective inhibitor of residual coagulant in cheese.
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