The proteolytic pathway of Lactococcus lactis

摘要

Mixed starter cultures used to manufacture Dutch cheeses are composed of lactic acid bacteria of which Luctococcus spp. are the dominant organisms (Hugenholtz 1986). Several metabolic properties of lactococci serve special functions which directly orindirectly have impact on processes such as flavour development and ripening of the cheese (Olson 1990), These functions are (i) fermentation and depletion of the milk sugar lactose; (ii) reduction of the redox potential; (iii) citrate fermentation and (iv) degradation of casein. The degradation of casein by lactococci yields peptides and amino acids that are the sources of essential and growth-stimulating amino acids for Lacto-coccus lactis (Thomas and Pritchard 1987; Chopin 1993), In addition to beingan important nutritional source for the starter culture bacteria, the casein degradation products also play a crucial role in the development of flavour in cheese. Certain peptides contribute to the formation of a typical cheese flavour, whereas others,undesirable bitter-tasting peptides, can result in an off-flavour. The need for a better understanding of the processes leading to the formation of these flavour peptides has prompted various research groups to study the components of the proteolytic pathway. Research on the proteolytic pathway of L. lactis is the most advanced. Most, if not all, of the components of this pathway have been identified, the majority of the enzymes purified and biochemically characterized, and the genetics of the corresponding genes studied (Table 1).