Rheological properties of acid gels prepared from heated milk fortified with whey protein mixtures containing the A, B and C variants of β-lactoglobulin

The effect of fortification of reconstituted skim milk with different levels of a whey protein mixture containing a 1:2 ratio of alpha -lactalbumin (alpha -1a) and different genetic variants of beta -lactoglobulin (beta -LG) on the rheological properties of acid milk gels, formed by acidification with glucono-delta -lactone, was investigated. Milk samples were either unheated or heated at 80 degreesC for 30min before acidification, Acid gels prepared from unheated skim milk had very low G' values, long gelation times and low gelation pH. Samples prepared from heated milk had markedly higher G' values, a reduced gelation time and an increased gelation pH. The addition of increasing levels of whey protein mixtures containing beta -LG B or beta -LG C to the milli prior to heating and acidification caused an almost linear increase in the G'. In contrast, whey protein mixtures containing beta -LG A caused a progressive increase in the G' with added protein levels up to about 0.7% (w/w) but little further change at higher addition levels. A mixture of the A and B variants of beta -LG gave an intermediate behaviour between those of the A and B variants. In all samples, the G' value at 5 degreesC was approximately twice that at 30 degreesC so that the relative differences as a result of the beta -LG genetic variants were similar for the two temperatures. (C) 2001 Published by Elsevier Science Ltd.