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Processing Variables Affecting Proteolysis in Yogurt During Incubation

Department of Food Science, The Pennsylvania State University, University Park 16802

ABSTRACT

The proteolytic activity of yogurt culture influences the keeping quality and consumer acceptance of commercial yogurt. In this study, proteolytic activities of five commercial yogurt cultures were investigated, as influenced by associative growth, total milk solids concentration, prior heat treatment of the milk, and incubation time. Proteolysis was monitored by liberation of alpha-amino groups per 100 ml milk. Associative growth inhibited proteolysis of four of the five cultures, but proteolytic activity was stimulated in one culture. Proteolysis was dependent on the total solids concentration of the milk and incubation time. The proteolytic activity of the cultures was similar. Minimum proteolysis occurred at 10% total milk solids and maximum proteolysis at 14.5% total milk solids. Proteolysis is dependent on the prior heat treatment of the milk. Pasteurization inhibited the acid production by culture CH3, but heat treatment did not influence the acid production by culture THY42. A complete understanding of these variables and their interactions can lead to the development of strategies to minimize proteolysis during the manufacture of yogurt.

¹ Aluminum Company of America, Alcoa Center, PA 15069.