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Summary
The effect of calcium content on some properties of co-precipitates in solution are considered. The solubility of the low-calcium type over a range of pH values was similar to casein, but 4% and 6% sodium tripolyphosphate was required for maximum solubility of medium- and high-calcium types. Some protein was insoluble at pH 7. and this appeared to be mainly aggregated whey protein and a sialic-acid-containing casein traction. A colloid mill was required to disperse the granular form of co-precipitate, and homogenizing was necessary to produce almost scdimenl-fiee solutions from both granular and spray-dried forms.
Solutions of co-precipitates were "whitened" to approximately the same opacity as skim milk by the addition of CaCl^sub 2^ under controlled conditions, or by homogenizing with fat. Sodium tripoly phosphate apprarcd 10 stabilizee these milk-like preparations towards heat sterilizing but lactose decreased both their stability and whiteness.
Introduction
A method for the continuous production of co-prccipiiales of casein and whey proteins with controlled calcium contents was described in Part 1 of [his scries (Muller et al, 1967). The three types of co-precipitate that have been manufactured commercially have been described as "low", "medium" and "high" calcium, and they contain 0.5-0.8%, about 1.5%, and 2.53.0% calcium respectively. One of the aims in making co-precipitates with a range of calcium contents was to produce proteins with different functional properties, thereby extending the potential use of co-precepitate in a variety of food products with different viscosity, hydration, solubility and "whiteness' requirements. This paper describes some of the solubility and whitening properties of several forms of co-precipitate.
For some purposes, a more or less clear solution of the co-precipitate is desirable, whereas in other producís, such as reconstituted milk-like drinks, a stable dispersion is required in order to impart a white, opaque appearance to the product.
Method
(i) Solubility
The effect of pH and sodium tri polyphosphate (STPP) on the solubility of commercial samples of co-precipitate was examined by a meihod based on the standard solubility index method. Australian Standard N 61 - 1965. Protein-water mixtures were stirred in a Cenco Solubility Index Mixer for a standard time, filtered, and the protein remaining in solution in the filtrate determined. Modifications to the standard method for measuring the solubility of skim milk powder...