Effects of pH and temperature on the water-holding capacity of casein curds and whey protein gels

Abstract

SummaryThe water-holding capacities of mineral acid casein (MAC) curd, rennet casein curd and whey protein concentrate (WPC) gel were determined as a function of pH and temperature by drainage of liquid on a stationary, horizontal screen. As precipitation pH was varied over the range 4·3–5·55, the water-holding capacity of MAC curd ranged from 2·4 to 5·2 g water/g dry casein with minimum water-holding capacity at precipitation pH 5·3. Samples of dried MAC curd over the same range of precipitation pH did not vary significantly in water-holding capacity, and all absorbed ∼2·0 g water/g dry casein. Both rennet casein curd and WPC (170 g total solids/kg) gels increased in water-holding capacity as the pH of the suspending liquid increased in the range 3·5–10, but the changes with pH were much smaller than for MAC curd. For both types of casein curd and for WPC gel, water-holding capacity decreased with increase in temperature in the range 5–90 °C. The results are interpreted largely in terms of changes in electrostatic interactions with pH and changes in hydrophobic interactions with temperature.