Abstract
The autolysis and proteolysis are important features in the strains of L. lactis used in the manufacture of cheese. The autolytic and proteolytic activity of L. lactis has been linked with the development of flavor and texture in the cheese. On the other hand, there is a growing interest in new strains isolated from raw-milk cheeses and vegetables. These wild-strains have showed different features of industrial importance in comparison with those observed in commercial cultures. However, it still not clear if the autolytic and proteolytic properties of these wild-strains differ from the industrial strains. The objective of this work was to assess the autolytic and proteolytic activities of 21 strains of L. lactis isolated from diverse sources. The rates of autolysis and proteolysis observed in vitro were highly strain-dependent. The pH and the NaCl concentration in the media affected significantly the autolysis of L. lactis. The strains isolated from vegetable showed in general low and medium autolytic activity, whereas the strains isolated from raw-milk cheeses had medium to high autolytic activity. The strain with highest proteolytic activity was a strain isolated from corn leaves. Although still not clear how this strain acquired this pronounced characteristic.
Highlights
Lactococcus lactis of the lactic acid bacteria (LAB) are more widely used as starter dairy culture on the manufacture of cheese [1]
Large variation in the percentage of autolysis was observed among the 21 strains of L. lactis (Figure 1)
Statistical analysis showed that pH, NaCl concentration and its interaction had a significant influence (P < 0.05) in the autolysis of L. lactis
Summary
Lactococcus lactis of the lactic acid bacteria (LAB) are more widely used as starter dairy culture on the manufacture of cheese [1]. The autolysis of Lactococcus lactis is a desirable trait, because most of the enzymes related with the production of flavor compounds are intracellular. The proteolytic system of L. lactis is composed essentially of proteinases that initially cleave the milk protein to peptides, and these peptides are cleaved into smaller peptides and amino acids by intracellular peptidases. Some of these amino acids are subsequently catabolized, producing a variety of flavor compounds like aldehydes, alcohols, carboxylic acids, esters and sulfur compounds [8,10,11]
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