Physico-Chemical Properties of Milk and Whey in Membrane Processing

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Abstract
Membrane processes covered by this review include ultrafiltration, reverse osmosis, and electrodialysis. General performance equations for these processes illustrate the effects of certain physico- chemical properties of skim milk and wheys on the process performance. Composition and molal concentrations of protein, lactose, and salt fractions are related to experimental, calculated, or handbook data for osmotic pressure, viscosity, and diffusivity of dairy fluids. The important contribution of milk salts to the total osmotic pressure in milks and wheys is emphasized. Comparison of various viscosity data demonstrates the effect of total protein concentration. Compositional and environmental changes during the membrane processes are discussed in view of possible effects of these changes on component solubility and related precipitation phenomena. Membrane processing of fluid foods has been growing in importance as an industrially applic- able processing technique, with the dairy industry playing a major role in this develop- ment. The principal dairy materials - milk and whey - are particularly suitable for membrane processing; in fact, whey is frequently used as a test medium for engineering research and design of membrane processes for other food applica- tions. This paper will review physico-chemical properties of skim milk and whey which affect performance in membrane processes used by the dairy industry. The review does not cover whole milk, until recently considered unsuitable for membrane processing due to its fat content.

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