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
2003
Zbikowska, A. | Szerszunowicz, I. (University of Warmia and Mazury, Olsztyn (Poland). Dept. of Food Biochemistry)
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 percent (significant differences at p=0.05). Electrophoretic analysis of the proteins in pellets after ultracentrifugation of the curds indicates that heating to 92 deg C caused an increase in the share of whey proteins by 1 percent on average. At the same time, a decrease in the share of beta-lactoglobulin (beta-lg) by 4.7 percent and BSA+Ig by 2.8 percent was noted in the proteins of the soluble fraction after ultracentrifugation of the curds. alphas- and beta-casein were not found in the soluble fractions. On the other hand, para-kappa-casein was found (from 2.3 percent in the unheated substrates to 2.7 percent in the substrates heated to 92 deg C). With acid-rennet coagulation heating the substrates at 92 deg C contributed to a decrease in the share of Ca and P in the pellets after ultracentrifugation of the curds by 1.8 percent and 1.7 percemnt, respectively, with the unchanged share of total N. The content of beta-lg, alpha-lactalbumin (alpha-la) and BSA+Ig in the soluble fractions of the curds in the substrates heated at 92 deg C decreased by 13.7 percent, 1.6 percent and by 3.9 percent, respectively. Heating the substrates at 92 deg C contributed to a decrease in the share of para-kappa-casein in the soluble fractions of acid-rennet curds from 1.7 percent to 0 percent. At the same time, it limited the incorporation of dissociated beta-casein into a gel network. Its content in the soluble fraction after ultracentrifugation of the curds increased from 0 percent in the case of the unheated substrates to 2.7 percent in those heated to 92 deg C
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