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The proteolytic and lipolytic activities of 108 yeast strains isolated from cheese whey and soft and hard cheese made in Argentinian dairy industries were studied by different methodologies. Proteolytic activity on Milk Agar (Merck) and Casein Medium [Czapeck Agar (Oxoid) + Casein (Merck)] was detected only in 21 strains (19.4% of total studied strains). The ortho-phthalaldehyde spectrophotometric assay (OPA test) showed a higher proteolytic activity in strains of Candida
, whereas lower and similar activity values were found in strains belonging to the genera Cryptococcus
. Casein degradation by yeasts was also investigated by High Pressure Capillary Electrophoresis. This methodology determined that a strain
of Candida crusei
strongly degraded the two genetic variants of β
-casein, as well as k
-casein. Lipolytic activity on Tributyrin Agar (Merck) was detected in 18 strains (16.6% of total studied strains). API-ZYM tests applied on strains of the predominant species exhibited mainly activities of alkaline phosphatase, esterase (C4), esterase lipase (C8), leucine aminopeptidase, valine aminopeptidase, cystine aminopeptidase and acid phosphatase. Therefore, yeasts growing in the cheese during manufacture may contribute to improvement of the quality of the final product through the changes caused during ripening, due principally to the activity of enzymes hydrolysing peptides and milkfat. The results obtained in this investigation could contribute to the adequate selection of strains for the dairy industry starters since the degree of proteolysis and the formation of flavor compounds are fundamental to the characteristics of the matured cheese. Although the maturation process is driven basically by the enzymes from milk and lactic acid bacteria of the starter, yeasts would also have a considerable degree of participation in this process.