GOATS MILK STABILITY DURING HEAT-TREATMENT - EFFECT OF PH AND PHOSPHATES

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 phosphat es addition, on goat's milk protein denaturation, final pH, and stabil ity of samples submitted to direct or indirect UHT (ultrahigh treatmen t). Samples at pH 6.7 heated at 140 degrees C and samples at pH 6.9 or higher and heated at 145 degrees C using the direct UHT method coagul ated. Significant differences in alpha-lactalbumin and beta-lactoglobu lin 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 pro tein denaturation where found on milk samples with 0.3 or 0.5 g/L phos phates, and a significant increase in alpha-lactalbumin denaturation w as found between the different temperatures assayed. Our results show that the changes in the pH or the addition of phosphates had little ef fect in the whey protein denaturation, but it affected the heat stabil ity of goat's milk. Samples heated at 135-150 degrees C using a UHT in direct method showed, in general, a higher stability for the milk samp les with added phosphates than those adjusted to alkaline pH.