A kinetic Study in the changes of SDS-PAGE profile of whey proteins during storage at different temperatures

Abstract

Whey is the soluble fraction of milk separated from the caseins during manufacture of rennetcoagulated cheese, (sweet whey) or use of acids (acid whey). Whey proteins are widely used in a variety
of foods, primarily for their superior functional properties such as gelling and emulsification. Solubility
is the major protein attribute affecting all functional properties. In this study, the effect of storage at
different temperatures on sweet and acid whey proteins solubility and gel electrophoresis pattern was
investigated. Acid whey was produced by adjusting the pH of pasteurized milk to 4.6 and sweet whey
was produced by adding microbial rennet to the pasteurized milk held at 37°C for 1 h. Whey samples
were stored at -18, 4, 25, 40 and 60°C. At different time intervals, samples were removed and used for
protein solubility determination and SDS-PAGE. Results showed that the solubility of proteins of both
whey types stored at -18 and 60°C significantly decreased, such that at -18o
C, 50 and 61% decrease for
sweet and acid whey protein solubility, respectively, occurred after 6 weeks. These decreases were 44
and 55% for samples stored at 60°C for 5 days. The decrease in solubility at 4, 25 and 40°C was less
drastic. At all temperatures, decrease in protein solubility followed a first order kinetic. The activation
energies for loss of protein solubility were 6.3 to 6.4 kcal/mol for sweet and acid whey proteins. The
SDS-PAGE patterns indicated significant denaturation and aggregation of major whey proteins during
storage