Enzyme Activities of Lactic Streptococci and Their Role in Maturation of Cheese: A Review

Abstract

Modification of the genome of economically important lactic streptococcal strains is of interest to improve starter cultures and thus the quality of dairy products. To date only limited Information is available about the enzyme potential of mutant as compared with parent strains of lactic streptococci. Initial action of cell-wall associated proteinases on casein and subsequent action of peptidases on peptides are crucial for normal growth and rapid acid production by streptococci in milk. Lactic streptococci used for cheese making contain a complex proteolytic/lipolytic enzyme system that is needed to modify texture and development of flavor in cheese. The mutant strains of lactic streptococci, lactose-negative and proteinase-negative, have higher amino-peptidase and dipeptidase and lower proteinase activities than their parents. Also, esterase and lipase activities of the mutants are greater than those of their parents. Successful propagation of proteinase-negative mutants to a high cell density is made possible by external pH control and use of whey-based media, and so their use in cheese manufacture is feasible. Altering of cell-wall associated proteinases of group N streptococci is important to control development of bitter flavor in cheese. Incorporation of lactose-negative, proteinase-negative mutants into cheese milk as an adjunct source of enzymes has enhanced development of flavor in cheese.