Impact of chymosin- and plasmin- mediated proteolysis on the growth and proteolytic activity of lactobacilli in miniature Cheddar-type cheeses

MILESI, MARÍA M.; MCSWEENEY, PAUL L. H.; HYNES, ERICA R.

Tucumán, Argentina

Simposio; II International Symposium on Lactic Acid Bacteria - First Argentinean LAB Net Meeting International; 2006

Centro de Referencia para Lactobacilos (CERELA)

[Publicación del resumen y presentación en formato póster] Strongly proteolytic lactic starters seem to improve the growth of NSLAB and adjunct cultures of lactobacilli in cheese, but no information is available about the potential impact of non-microbial proteases usually active during cheese ripening on NSLAB growth. The objective of this work was to study the influence of chymosin- and plasmin-mediated proteolysis on the growth and biochemical activities of lactobacilli in miniature Cheddar-type cheeses manufactured under controlled microbiological conditions. Cheeses with different levels of proteolysis were made in two different trials, by adding a strong chymosin inhibitor (pepstatin) or by increasing plasmin activity by the addition of a mixture of plasminogen, and its activator, urokinase. An adjunct culture of L. plantarum isolated from cheese was added into the samples with different extent of proteolysis. Proteolysis during cheese ripening (60 days) was assessed by means of electrophoresis, liquid chromatography and total content of free amino acids. Chymosin and plasmin activities were also quantified. Microbial counts for starter lactococci, adjunct lactobacilli and NSLAB were performed during ripening. Results showed that pepstatin significantly inhibited residual chymosin, which caused a drastic decrease in as1-casein hydrolysis, detected both by electrophoresis and peptide mapping. Free amino acids content was also diminished in cheeses with reduced chymosin activity. Increased plasmin activity, on the other hand augmented the breakdown of b-casein with production of γ-caseins, but the impact in secondary proteolysis was low. In all cases, proteolysis increased with ripening time. The development of the adjunct culture of L. plantarum was not influenced by chymosin- or plasmin-mediated proteolysis, as well as the growth of the NSLAB in cheeses without the addition of an adjunct culture. The proteolytic and peptidolytic activity of lactobacilli was not higher in cheeses with an extensive primary proteolysis than in those in which this transformation was inhibited or diminished. It was concluded that chymosin- and plasmin-mediated proteolysis is not a limiting factor for the development and proteolytic-peptidolytic activities of lactobacilli in the cheese model studied.