Goat's Milk Stability during Heat Treatment:  Effect of pH and Phosphates

Abstract

Goat's milk stability during heat treatments is lower than that of cow's milk. We have studied the influence of two factors, pH and phosphates addition, on goat's milk protein denaturation, final pH, and stability of samples submitted to direct or indirect UHT (ultrahigh treatment). Samples at pH 6.7 heated at 140 °C and samples at pH 6.9 or higher and heated at 145 °C using the direct UHT method coagulated. Significant differences in α-lactalbumin and β-lactoglobulin denaturation were found between milk samples adjusted to different pHs and submitted to different temperatures. No coagulation was found in samples with added phosphates. Significant differences in whey protein denaturation where found on milk samples with 0.3 or 0.5 g/L phosphates, and a significant increase in α-lactalbumin denaturation was found between the different temperatures assayed. Our results show that the changes in the pH or the addition of phosphates had little effect in the whey protein denaturation, but it affected the heat stability of goat's milk. Samples heated at 135−150 °C using a UHT indirect method showed, in general, a higher stability for the milk samples with added phosphates than those adjusted to alkaline pH. Keywords: pH; phosphates; goat's milk; heat stability