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Journal of Dairy Science Vol. 67 No. 2 263-269
© 1984 by American Dairy Science Association ®
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Strength of Rennet Curd Made from Milk and Chemically Modified Soy Proteins1

Y. H. Lee2 and R. T. Marshall

Department of Food Science and Nutrition, University of Missouri, Columbia 65211

ABSTRACT

Strength of curd and concentration of protein in whey were used to study effects of adding native soy protein and chemically modified soy proteins to milk used to make rennet curd. An Instron food testing system was used to measure curd strength 15 min after addition of rennet to reconstituted nonfat dry milk mixtures with glucono-{delta}-lactone. Clarified whey, collected after extrusion testing, was tested for protein content by measured absorbancy at 280 nm. Soy protein, added as 20% of the total protein, lowered curd strength compared with strength of curd of reconstituted nonfat milk. This treatment also increased protein in the whey to .60% compared with .48% in the control that contained water instead of soy protein solution. Curd strength was decreased further and losses of protein were increased when added soy proteins were modified by acetylation, succinylation, or alkylation. Bulky and neutral reagents, N-ethylmaleimide, glycine methyl ester, and carbodiimide had a similar effect. Decreasing the negative charge on soy protein or treating it with alkali had the opposite effect. We speculated that soy protein in milk interfered with electrostatic and hydrophobic interactions among rennet-treated casein micelles.

FOOTNOTES

1 Contribution from the Missouri Agricultural Experiment Station, Journal Series No. 9233.

2 Mead Johnson and Co., Evansville, IN 47721.






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Copyright © 1984 by the American Dairy Science Association ®.