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Proteolysis and Curd Tension in Milk Associated with Accelerated Starter Culture Growth^{1, 2,}

Department of Food Science, North Carolina State College, Raleigh

ABSTRACT

Growth rate of mixed strain streptococcus starter cultures in milk were comparable, although the cultures showed a twofold difference in proteolytic activities. The strength of the curd formed in milk varied as much as 60 g between cultures at the same titratable acidity and also was not related directly to proteolytic activity of cultures. The addition of up to 1.2 mg pancreas extract per milliliter of milk caused a twofold reduction in proteolysis by the cultures, and a concomitant increase in the curd strength at least twice that of the control culture. The proteinase system of the streptococci appeared to be adaptive, since cells grown in a medium containing only casein as a nitrogeneous source possessed greater proteolytic activity than when grown in the medium fortified with simpler nitrogenous compounds contained in pancreas extract. The natural or induced variations in proteolysis and curd tension of starter cultures may be important in determining characteristics and yield of cheese curd.

¹ Contribution from the Department of Food Science and Processing, North Carolina Agricultural Experiment Station, Raleigh, North Carolina. Published with the approval of the Director of Research as Paper No. 1393 of the Journal Series.

² Supported in part by a grant from the American Dairy Association.