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Department of Dairy Technology, The Ohio State University, Columbus
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.
1 Article no. 11–66, Department of Dairy Technology. This investigation was supported by Public Health Service Research Grant no. EF-00205-03 from the Division of Environmental Engineering and Food Protection.
2 Present address: Department of Food Science and Industries, University of Minnesota, St. Paul.
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