Micellar Changes in Skimmilk Treated with Alkali or Acid

Abstract

Samples of skimmilk adjusted to various pH levels between 1 and 12 with N-KOH or N-HC1, were restored to the original pH after 3 hr. at 20C. Differences in rennet coagulability, turbidity, and soluble salts resulted from such treatment. Rennet coagulation times of milks transiently above pH 10 increased logarithmically with increasing pH. Milk transiently at an acid pH coagulated more rapidly. Colloidal Ca and P which was nearly constant in milks at a higher pH gradually decreased in milks at a lower pH. Insoluble Ca3(PO4)2 forms slowly, and there was no detectable change in 3 hr. under experimental conditions. Turbidity decreased above pH 8.7 and below ph 5.4. The miscelles were swollen and altered by pH changes, but colloidal Ca3(PO4)2 was not disturbed in the alkali range. The rapid decrease of rennet coagulation time in milks transiently at low pH was attributed to the increase of soluble Ca. The logarithmic increase in coagulation time in milks treated above pH 10 was attributed to protein changes that altered micellar interaction and liberated H2S.