Some Effects of Pyrophosphate and Citrate Ions Upon the Colloidal Caseinate-Phosphate Micelles and Ultrafiltrate of Raw and Heated Skimmilk

Abstract

The effect of added pyrophosphate (TSPP) ions, citrate ions, and heat upon the following properties of skimmilk were investigated: a) apparent size and chemical composition of the colloidal caseinate-phosphate micelles, b) chemical composition and Sephadex gel filtration properties of the resulting ultrafiltrate, and c) ultracentrifugal sedimentation characteristics of caseinate-phosphate micelles dispersed in phosphate buffer, treated with oxalate, or dialyzed against TSPP. Heating skimmilk containing TSPP and citrate ions resulted in substantial disaggregation of the colloidal caseinate-phosphate micelles. The resulting micelles in heated TSPP-skimmilk contained greater proportions of calcium phosphate; whereas, those in heated citrate-skimmilk contained smaller proportions of calcium phosphate than those sedimented from control skimmilk. Added TSPP ions resulted in lower levels of ultrafilterable calcium but higher levels of ultrafilterable inorganic phosphate; whereas, added citrate ions caused an increase in both the ultrafilterable calcium and inorganic phosphate over those of the control. Heating TSPP-and citrate-skimmilk resulted in minor additional changes in the amount of ultrafilterable calcium phosphate. Sedimentation experiments showed that TSPP ions disaggregated the colloidal caseinate-phosphate micelles from heated TSPP-skimmilk more effectively than those from heated control skimmilk and to a much greater extent than was produced by removal of calcium with oxalate. © 1967, American Dairy Science Association. All rights reserved.