Aspect qualitatif de l'activité protéolytique des lactobacilles thermophiles utilisés en fabrication de fromages à pâte pressée cuite

Abstract

-Qualitative aspect of proteolytic activity of thermophilic lactobacilli using in Swiss cheeses. The average peptidic pattern was established from 253 French Emmental cheeses sampled in 50 factories. It contained 53 peptidic peaks, 4 of which were the most important in quantity. Two Lactobacillus helveticus strains and five Lactobacillus delbrueckii ssp. lactis strains were tested in Emmental experimental cheesemaking in association with three different propionic strains (21 cheeses). The Propionibacterium freudenreichii strains did not affect the peptidic pattern of ripened Emmental cheese. On the other hand, 13 peptidic peaks were significantly influenced by the thermophilic lactobacilli strain. The two species of thermophilic lactobacilli were discriminated by three peptidic peaks. Seven peptidic peaks were correlated with the ammonia amount in ripened Emmental cheese. No significant correlation was found between peptidic peaks and SN/TN and NPN/TN. At the same time, the peptidic pattern produced by the seven lactobacilli strains were studied in laboratory. The most specific peptidic peak of the French Emmental cheese were not found by using the Hammarsten casein as substrate. Another substrate, similar to hard cooked cheeses, lyophilized and sterilized by ionisation was tested. This substrate was obtained with microfiltered milk and Streptococcus thermophilus strains only. This substrate digested by thermophilic lactobacilli allowed to find the specific peptidic peaks of the French Emmental cheese. For example, the 14th peak obtained in laboratory was significantly different according to lactobacilli species, as it was observed in the Emmental cheese experiments. This peak distinguished the strains inside the Lb. delbrueckii ssp. lactis too.

Production of peptides and free amino acids in a sterile extract describes peptidolysis in hard-cooked cheeses

“…free amino acids, during cheese ripening (Chopard, Schmitt, Perreard, & Chamba, 2001;Hannon, Kilcawley, Wilkinson, Delahunty, & Beredsford, 2007;Hynes et al, 2003;Mäyrä-Mäniken & Bigret, 1998). This contribution varies highly from one strain to another; L. helveticus strains differentiate not only in the intensity of their caseinolytic activities but also in the specificity of their endopeptidases (Jensen, Vogensen, & Ardö, 2009).…”

Impact of the proteolysis due to lactobacilli on the stretchability of Swiss-type cheese

“…However, L. helveticus and L. delbrueckii subsp. lactis differ in both their proteinase and peptidase activities, as illustrated by the RP-HPLC pattern of peptides observed in Swiss cheese [2]. A complete characterisation of the proteolytic equipment and of the autolytic properties of the strains would probably be required to understand their potential to enhance stretchability.…”

Acquisition of PrtS in Streptococcus thermophilus is not enough in certain strains to achieve rapid milk acidification

“…When strains were grown in milk, caseins were first eliminated by adding to 40 volumes of fermented milk, 5.3 volumes of saline solution (NaCl 0.85%; sodium glycerophosphate 0.5%; Tween 80 0.1%; pH 7), and 1.3 volume of trisodium citrate 1 mol.L −1 (Chopard et al 2001). Pellets were recovered by centrifugation for 15 min at 3900g and 4°C, washed and resuspended in Tris-HCl buffer 100 mmol.L −1 pH 7.0 to obtain a cell concentration of 5.10 8 CFU mL…”

“…After growth in 80 mL of milk, caseins have been removed as described above (Chopard et al 2001) and bacterial pellets were resuspended in 46.6 mL of cold extraction buffer (sodium phosphate 5 mmol.L…”