Proteolytic systems in lactic acid bacteria

Abstract

Lactic acid bacteria (LAB) have a very long history of use in the manufacturing processes of fermented foods and a great deal of effort was made to investigate and manipulate the role of LAB in these processes. The proteolytic activity of LAB is essential for their growth and contributes significantly to flavor development in fermented products. LAB has a complex proteolytic system capable of converting milk casein to the free amino acids and peptides necessary for growth and acid production. This system is composed of a proteinase which is involved in the initial cleavage of casein, peptidases which hydrolyze the large peptides formed and transport systems which are involved in the uptake of small peptides and amino acids. Much of the research hitherto has focused on the proteinase of lactococci but increasingly interest is now being directed towards other industrially-important genera of lactic acid bacteria, in particular, lactobacilli. As part of the industrial processes, LAB are challenged by various stress conditions that affect their metabolic activities, including proteolysis. The stress responses related to proteolysis in LAB is principally based on studies on Lactococcus lactis and Oenococcus oeni. Several of these proteinases have been purified and characterized at a biochemical level and there are reports on the cloning, sequencing and genetic analysis of some of them. Certain Lactobacillus strains are believed to produce bioactive health-beneficial peptides from milk proteins. The casein molecules of milk are of particular interest because they are known to harbor bioactive peptides that are latent until released by proteolysis. In the last years it was characterized a proteolytic system in lactic acid bacteria from wine. The extracellular protease of O. oeni is expressed in stress conditions and it is effective on the nitrogenous macromolecular fractions of red and white wines.