摘要 : The relative contributions of rennet, starter and plasmin to proteolysis during storage of quarg were investigated. In the experimental design used, each agent was, in separate treatments, either omitted (rennet), replaced by a no... 展开 The relative contributions of rennet, starter and plasmin to proteolysis during storage of quarg were investigated. In the experimental design used, each agent was, in separate treatments, either omitted (rennet), replaced by a non-proteolytic substitute (glucono-delta-lactone instead of starter) or either increased by the addition of exogenous enzyme or decreased by addition of a specific inhibitor (plasmin). A final experimental variable involved heating milk to 90鳦 for 10 min prior to acidification. All quarg samples were thermized after acidification, to reduce levels of adventitious microflora and to extend shelf life. The experimental treatments used had little effect on composition or yield of quarg, with the exception of high heat treatment, which increased yield and moisture content due to whey protein denaturation. Omission of rennet during manufacture significantly reduced proteolysis during ripening of quarg, and altered urea-PAGE and reversed-phase HPLC patterns of proteolysis. Omission of starter had a considerably lesser effect. The role of plasmin was also minor, resulting in production of the large water-insoluble gamma-caseins. The principal ripening agent in thermized quarg was rennet, while starter enzymes and plasmin playeda lesser role. 收起