Viscosity changes in concentrated skim-milk treated with alkali, urea and calcium-complexing agents: II. The influence of concentration, temperature and rate of shear

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Abstract
An essentially exponential relationship between maximum viscosity and concentration of casein was observed for concentrated skim-milk undergoing treatment with calcium hydroxide. Positive temperature coefficients of viscosity were found for samples treated with alkali, while negative coefficients were found with sodium hexametaphosphate. The time of appearance of the maximum viscosity was independent of temperature in concentrated skim-milk treated with sodium or calcium hydroxide; however, when sodium hexametaphosphate was used the maximum appeared earlier at higher temperatures. The viscosity of all systems studied decreased with increasing rate of shear, the deviation from Newtonian being greatest when the viscosity was at its maximum. The effects are explained in terms of a swelling and disintegration of the casein micelles as was postulated in the previous paper. The authors wish to thank Miss Audrey K. Morris, Dairy Research Section, C.S.I.R.O., Melbourne, for valuable technical assistance, and to express their appreciation for the helpful advice of other members of this Section during the preparation of the manuscript.