Proteolysis During Cheese Manufacture and Ripening

Abstract

Proteolysis in cheese can be divided into three phases: proteolysis in milk before cheese manufacture, the enzymatically induced coagulation of the milk, and proteolysis during cheese ripening. Extracellular proteinases from psychrotrophs may cause reduced cheese yields and off-flavors, but the problem does not appear to be significant at populations <106 cfu/ml. Proteinases from leucocytes may also reduce yields, but these are less active than bacterial proteinases. Plasmin (indigenous milk proteinase)causes significant hydrolysis of β-casein, especially in late lactation, but because most of this occurs prior to milking, yield losses due to plasmin activity (i.e., via formation of proteose peptones) are largely unavoidable. Coagulation of milk for rennet cheeses is accomplished by the specific cleavage of the casein micelle-stabilizing protein, κ-casein, at the phenylalanine (105)-methionine (106) bond by acid proteinases (rennets). The significance of the primary, secondary, and tertiary structures of κ-casein on the sensitivity of this bond is now established, as are pH, ionic strength, temperature, heat treatment of milk, and environmental and processing variables. Proteolysis is probably the most important biochemical event during the ripening of most cheese varieties, with a major impact on flavor and texture. Techniques have been developed that permit quantitation of the principal ripening agents to proteolysis, i.e., rennet, milk proteinase, and the proteinases from starter, nonstarter bacteria, and perhaps secondary inocula. The contribution of each of these agents to proteolysis in the principal varieties has been established in general terms. Several techniques have been used to monitor and quantify proteolysis in cheese during ripening; the principal of these are described and evaluated. Standardization of analytical techniques for assessing proteolysis in cheese appears warranted. © 1989, American Dairy Science Association. All rights reserved.