Dj. Oldfield et al., KINETICS OF DENATURATION AND AGGREGATION OF WHEY PROTEINS IN SKIM MILK HEATED IN AN ULTRA-HIGH TEMPERATURE (UHT) PILOT-PLANT, International dairy journal, 8(4), 1998, pp. 311-318
Skim milk was subjected to various temperature-time (70-130 degrees C
for 3-1800 s) treatments in a pilot-scale ultra-high temperature (UHT)
plant using a direct steam injection (DSI) system. The rates of denat
uration and aggregation of beta-lactoglobulin (beta-lg) and alpha-lact
albumin (alpha-la) were determined by quantitative polyacrylamide gel
electrophoresis while that of immunoglobulin G (IgG) was determined by
affinity chromatography. The order of reaction, the rate constant and
the activation energy were determined for the denaturation of beta-lg
, alpha-la and IgG using non-linear regression methods. The kinetic pa
rameters obtained for beta-lg and alpha-la showed a marked temperature
dependence. Aggregation of beta-lg mainly involved the formation of i
ntermolecular disulphide linkages at all temperatures studied, while t
he aggregation of alpha-la, particularly below 80 degrees C, appeared
to also involve hydrophobic interactions. The kinetic parameters obtai
ned for beta-lg aggregation, due to disulphide bond formation, were si
milar to those observed for beta-lg denaturation. (C) 1998 Elsevier Sc
ience Ltd. All rights reserved.