EFFECT OF HEATING THE SOLUTIONS OF MILK PROTEIN CONCENTRATE ON THE COMPOSITION OF PROTEINS, CA AND P IN A GEL NETWORK AFTER RENNET AND ACID-RENNET COAGULATION.
 
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Pol. J. Food Nutr. Sci. 2003;53(2):37–41
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ABSTRACT
The aim of the research was to study the effect of heating the water solutions (pH 7.1) of the milk protein concentrate obtained with ultrafiltration on the content of nitrogen (N), calcium (Ca) and phosphorus (P) and the composition of proteins in the pellets after the ultracentrifugation of rennet curds (pH 6.6) and acid-rennet curds (pH 6.0). It was found that heating the concentrate solutions did not have any influence on the content of Ca and P in the insoluble fractions of rennet curd. However, it contributed, irrespective of the temperature of heating, to an increase in the share of total N by 0.3 % (significant differences at p=0.05). Electrophoretic analysis of the proteins in pellets after ultracentrifugation of the curds indicates that heating to 92°C caused an increase in the share of whey proteins by 1 % on average. At the same time, a decrease in the share of b-lactoglobulin (b-lg) by 4.7 % and BSA+Ig by 2.8 % was noted in the proteins of the soluble fraction after ultracentrifugation of the curds. as- and b-casein were not found in the soluble fractions. On the other hand, para-k-casein was found (from 2.3 % in the unheated substrates to 2.7 % in the substrates heated to 92°C). With acid-rennet coagulation heating the substrates at 92°C contributed to a decrease in the share of Ca and P in the pellets after ultracentrifugation of the curds by 1.8 % and 1.7 %, respectively, with the unchanged share of total N. The content of b-lg, a-lactalbumin (a-la) and BSA+Ig in the soluble fractions of the curds in the substrates heated at 92°C decreased by 13.7 %, 1.6 % and by 3.9 %, respectively. Heating the substrates at 92°C contributed to a decrease in the share of para-k-casein in the soluble fractions of acid-rennet curds from 1.7 % to 0 %. At the same time, it limited the incorporation of dissociated b-casein into a gel network. Its content in the soluble fraction after ultracentrifugation of the curds increased from 0 % in the case of the unheated substrates to 2.7 % in those heated to 92°C.
ISSN:1230-0322