Possible Role of Yeast Endoproteinases in Ripening Surface-ripened Cheeses

Yeasts isolated from smears of Trappist-type cheese were studied for their proteolytic activity. Of the three strains chosen for study, one was classified as Debaryomyces and two were strains of Trichosporon . The Trichosporon cultures were distinctly proteolytic when grown in skimmilk, whereas the Debaryomyces showed litle proteolysis in skimmilk culture except when grown with Streptococcus lactis . Autolysis of the yeasts yielded an endoproteinase active on a casein substrate through a pH range of 5.0 to 7.0, with peak activity at pH 5.8. Conditions for the production of proteolytically active autolysates and for obtaining maximum activity when acting on the substrate were studied. These conditions would occur during the ripening period of the surface-ripened cheeses, lending support to the view that the yeast endoenzymes serve as ripening agents.