RAPID ENZYMATIC METHOD FOR BIOTYPING AND CONTROL OF LACTIC-ACID BACTERIA USED IN THE PRODUCTION OF YOGURT AND SOME CHEESES

Determination of enzymatic patterns of 30 strains of Streptococcus thermophilus and 18 strains of Lactobacillus delbrueckii subsp. bulgaricus with a rapid APIZYM method was carried out. Alkaline and acid phosphatase, naphthol-AS-BI-phosphohydrolase, 10 esterases, 20 glycosidases, 61 peptidases and 2 proteases (trypsin and chymotrypsin) were included. The strains investigated were isolated from yogurt and from different starters used for different Italian cheeses. For S. thermophilus, all strains were positive for 3 glycosidases, 4 monopeptidases, 9 dipeptidases, 1 tripeptidase and all were negative for 2 esterases; 9 glycosidases; 8 peptidases and trypsin. For L. delbrueckii subsp. bulgaricus it was observed that all strains were positive for 2 esterases; 2 glycosidases; 11 monopeptidases, 9 dipeptidases, 2 tripeptidases and 1 tetrapeptidase and all were negative for alkaline-phosphatase; 3 esterases, 7 glycosidases, 5 monopeptidases, 2 dipeptidases. The defined enzymatic pattern of starter cultures can be used for predicting their suitability for dairy fermentations and for monitoring their stability as well as for typing.