HEAT STABILITY OF MILK AS AFFECTED BY VARIATIONS IN PH AND MILK SALTS

The maximum and minimum heat stability exhibited by most milks over a relatively narrow range of pH values is shown also by synthetic colloidal calcium caseinate-calcium phosphate systems and even by simple caseinate systems, provided all possess adequate contents of β-lactoglobulin, soluble calcium and phosphate. The phenomenon is not, however, dependent on the presence of the characteristic micellar structure of the casein of milk. The minimum stability observed, usually around pH 6.9, is the most characteristic feature of the phenomenon and arises from heat induced deposition of calcium phosphate on a caseinate/β-lactoglobulin complex. This reaction, which tends to occur to a marked degree at relatively high pH values and calcium ion concentrations, sensitizes the complex to precipitation by calcium ions. The precise pH values at which the maximum and minimum stabilities occur can vary depending on the salt composition of the serum, since the latter can influence the solubility of calcium phosphate. © 1969, Proprietors of Journal of Dairy Research. All rights reserved.