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Journal of Dairy Science Vol. 57 No. 9 992-997
© 1974 by American Dairy Science Association ®
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Effect of pH, Calcium, and Heat Treatment on Curd Tension of Casein Fraction Fortified Skim Milk1

D. L. Schultz and U. S. Ashworth

Department of Food Science and Technology, Washington State University, Pullman 99163

ABSTRACT

The effect of {alpha}- or ß-casein fortification (12 to 28% above control at 3.3% total protein) on skim milk curd strength was studied. After addition of 1 N hydrochloric acid to pH 6.0, {alpha}-casein fortified skim milk produced a weaker curd than ß-casein fortification. With added calcium chloride (.01 M), both fractions formed a firmer curd with {alpha}-casein slightly stronger than ß-casein.

Alpha and ß-casein fortified skim milk cultured with Streptococcus lactis had similar curd tension within a pH range of 5.20 to 5.85. Calcium addition (.01 M) increased {alpha}-casein fortified skim milk curd tension but had a depressing effect on ß-casein as compared to their respective curd strengths without added calcium. However, as pH approached 5.20, ß-casein curd strength increased faster per pH unit than that of the {alpha}-casein fortified samples.

Heat treatments within an effective heat range of .05 to .42 (holding time 10 min) allowed {alpha}-casein fortified skim milk to form a stronger curd than that fortified with ß-casein. When compared to unfortified skim milk, the greatest difference in curd tension between the {alpha}- and ß-casein fortifications was at effective heat .42. Alpha casein curd tension was reduced nearly three times as fast as ß-casein when skim milk fortified samples were heated at .42 in the presence of .005 M calcium chloride addition.

FOOTNOTES

1 Scientific Paper No. 4178, Washington Agricultural Experiment Station, Pullman, Project No. 1809.






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Copyright © 1974 by the American Dairy Science Association ®.