Proteolytic systems of lactic acid microorganisms: a review

Abstract

Introduction. The primary objective of this review is to analyze and summarize the existing scientific information about the structure features, formation conditions and properties of proteinases and peptidases of lactic acid microorganisms, which are widely used in the production of dairy products. Material and methods. The proteolysis of milk proteins, occured by lactic acid microorganisms, is an investigation object of this review article. Scientific articles as well as theses and monographs of microbiology, biochemistry and dairy science have been analysed. Methodology of the investigation is based upon the use of the methods of analysis, comparison and synthesis. Results and discussion. Cleavage of proteins and amino acids with enzymes of lactic acid and propionic acid bacteria promotes the enrichment of dairy products with nitrogen-containing and nitrogenfree compounds, and as a result, the product obtains necessary consistency, taste and smell. In addition to providing organoleptic properties, the formation of a large number of peptides with different types of biological activity occurs also in the process of proteolysis of milk proteins in the production of dairy products. The proteolytic system of lactic acid bacteria consists of three parts: proteinases, which that provide the initial cleavage of casein to peptides with formation of a large number of oligopeptides; peptidases, which cleavage peptides to amino acids; transport system, which provides transfer of proteolysis products through the cytoplasmic membrane. Proteinases function outside microbial cells, produce them, and peptidases-in cells of lactic acid bacteria. By the specificity of the effect on the fractions of the casein complex of milk proteinases of lactic acid microorganisms are divided into 2 types-РІ and РІІІ. Proteinases РІ are able to cleavage β-caseins and don't cleavage α S1-and κ-caseins, but proteinases РІІІ hydrolyse all three fractions:  S-, and caseins. None of the peptidases with carboxypeptidase activity were revealed among large number of lactic acid bacteria peptidases. PepN, PepС, РерА are referred to the aminopeptidases, found in lactic acid microorganisms. In addition to aminopeptidase, dipeptidases and tripeptidases were revealed in lactobacilli. Conclusion. It is recommended to use systematized characteristics of proteinases and peptidases of appropriate microorganisms with the purpose of providing quality organoleptic parameters of dairy products as well as the formation of biologically active peptides in the process of selecting the species composition of starter cultures.