EFFECT OF PH ON THE SURFACE HYDROPHOBICITY OF PROTEINS FORMING AN ENZYMATIC GEL NETWORK IN UNHEATED AND HEATED SOLUTIONS OF MILK PROTEIN CONCENTRATES.
 
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Pol. J. Food Nutr. Sci. 2005;55(1):75–78
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ABSTRACT
The objective of the present study was to compare changes in the surface hydrophobicity of proteins forming a rennet gel network at pH 6.6 and 6.0. The substrates were unheated and heated (72°C/15 s; 92°C/60 s) aqueous solutions of milk protein concentrate (protein concentration 3.3%). The contents of nitrogen, calcium and ANS (nmol ANS/mg protein) bounded to protein particles sedimented during ultracentrifugation of curds and substrates (insoluble fractions after ultracentrifugation (110 000 g, 1 hour) were determined. There were no significant differences in the calcium to protein ratio in the curd matrices obtained from unheated and heated (72°C/15 s; 92°C/60 s) substrates. At pH 6.6 the index of ANS binding by insoluble proteins after curd ultracentrifugation was by 1.3%, 3.5% and 2.3% lower, compared with the corresponding substrate fractions. This suggests that not only hydrophobic domains of para-k-casein, formed during the enzymatic phase of coagulation, were used for gel network formation. At pH 6.0 significant differences (p=0.05) between the indices of surface hydrophobicity of insoluble proteins after ultracentrifugation of curds and substrates were observed only in the case of concentrate solutions heated at 92°C (ΔANS = 0.14 nmol/mg protein), which may indicate a lower level of utilization of hydrophobic domains formed after proteolysis of κ-casein.
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