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Journal of Dairy Science Vol. 42 No. 4 589-597
© 1959 by American Dairy Science Association ®
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Factors Affecting the pH of Skimmilk Coagulation by Lactic Culture1

D. B. Emmons2, W. V. Price and A. M. Swanson

Department of Dairy and Food Industries, University of Wisconsin, Madison

ABSTRACT

The A-C (acid-coagulation) test measures the stage of gel formation in acid-coagulated skimmilk at which the gel will first shrink and expel whey when cut with a knife. This test was chosen to study certain factors influencing the pH of coagulation of skimmilk by action of lactic culture. The rate of acid development and the use of different commercial lactic cultures did not affect the pH at the A-C end-point. Increased amounts of rennet added early in the fermentation process caused the skimmilk to coagulate at progressively higher pH values, but very small additions had little or no effect. Different skimmilks did not respond alike to variations of rennet. Additions of chloride salts of calcium and sodium decreased the pH at the A-C end-point more than did monosodium phosphate or a mixture of "milk salts" when all were added to increase the ionic strength by 0.10 at pH 4.70. The pH at which the A-C end-point occurred decreased as the total solids in reconstituted nonfat dry milk increased, probably because of the greater ionic strength of milk salts in reconstituted nonfat dry milk with high total solids. Heat treatments of skimmilk which denatured whey proteins resulted in an increase in the pH at which the A-C end-point occurred.

FOOTNOTES

1 Published with the approval of the Director, Wisconsin Agricultural Experiment Station, Madison.

2 Present address: Dairy Technology Research Unit, Canada Department of Agriculture, Ottawa, Ontario, Canada.






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Copyright © 1959 by the American Dairy Science Association ®.