Content area
Full Text
Summary
Proteolysis involving enzymes from the starter bacteria, nonstarter bacteria, coagulant and milk contributes significantly to cheese flavour development. Generally, these enzymes have been well characterised and, in the case of the starter bacteria which have a primary role in cheese ripening, the specificity of action and localisation of the extracellular proteinase and an array of peptidases has been established. Membrane transport systems for peptides and amino acids have been elucidated and significant progress made towards understanding autolysis and the consequent release of intracellular enzymes by starter bacteria. Much of this work has been carried out in vitro and therefore variations in activity and specificity of the various enzymes in the complex cheese environment are likely. Salt concentration, pH, water activity, temperature, duration of incubation and an array of substrates produced by other proteinases will affect the peptidase released from starter and non-starter organisms. Degradation of peptides and further metabolism of amino acids is further influenced by variations in the autolytic ability and physical state of the various lactic acid bacteria in cheese. Protein metabolism studies in the cheese matrix are difficult but direct analysis of the 'cheese juice' extracted using a high pressure press may assist in understanding the process.
Introduction
Mesophilic starter cultures used for the manufacture of cheese are composed mainly Of Lactococcus lactis subsp. lactis and Lc. lactis subsp. cremoris strains. Their principal function is the uniform production of lactic acid at a predictable rate, which is necessary to produce good quality cheese. More specifically, acid production affects coagulant activity, denaturation and retention of the coagulant in the curd, curd strength, gel syneresis and the level of dissolution of colloidal calcium phosphate which influences cheese theological properties (Fox 1996). The production of lactic acid also helps control the growth of many species of adventitious organisms in cheese. A further major function of cheese starter bacteria is their contribution to the development of cheese flavour, particularly in the area of milk protein degradation.
Proteolysis in cheese is possibly the most important and complex of the three primary events - glycolysis, lipolysis and proteolysis - involved in the development of cheese flavour and texture. In addition to the starter bacteria, there are a number of other proteolytic agents in cheese...