Influence of pH, Casein, and Whey Protein Denaturation on the Composition, Crystal Size, and Yield of Lactose from Condensed Whey

Abstract

Lactose was crystallized from condensed whey under varying conditions of pH (3.76, 4.84, 5.59, and 6.43), degree of protein denaturation (4.2, 32.2, 46.9, and 78.4%), and casein addition (.2, .3, and .45%). Increasing the amount of whey protein denaturation in the condensed whey resulted in crude lactose containing more protein and ash, particularly when near the isoelectric point for whey proteins. Excessive whey protein denaturation increased viscosity of the mother liquor, decreased lactose crystal size, and made washing of the crude lactose more difficult. Casein had no adverse effects on lactose quality, yield, or crystal size. Generally, the yield of washed/dried lactose increased as whey protein denaturation increased from 4.2 to 46.9%; however, this was due mainly to inclusion of protein and mineral in the crystallized lactose, particularly at pH 4.84. Moderate protein denaturation (up to 32%) had no adverse affect on lactose quality. Washed/dried lactose prepared from condensed whey (pH 4.84 and 78.4% whey protein denaturation) contained excessive protein (5.0%) and ash (2.0%). Lactose quality improved with lower amounts of whey protein denaturation and crystallizing at pH on either side of the isoelectric point. © 1986, American Dairy Science Association. All rights reserved.