Interactions between milk proteins influence of heat calcium and lactose ii. interactions between alpha 51 casein and beta casein with beta lactoglobulin
Lebensmittel-Wissenschaft und -Technologie 25(2): 113-119
ISSN/ISBN: 0460-1173 Accession: 007474189
The interactions between .alpha.s1-casein and .beta.-casein with .beta.-lactoglobulin (.beta.-lg) in a 30 mM sodium barbital buffer of pH 7.00, heated at 25, 80 and 95.degree.C for 30 min and at 115.degree.C for 10 min, were investigated by studying the changes in their calcium binding and by polyacrylamide gel electrophoresis. The influence of lactose and calcium on these interactions was also investigated. Heating a mixture of .alpha.s1-casein and .beta.-lg at 80, 95 or 115.degree.C had no effect on calcium-binding, when measured at a calcium concentration of 3 mM, compared to samples treated at 25.degree.C. Heating the same solution at 80 or 95.degree.C without calcium (or lactose), the calcium binding at a calcium concentration of 10 mM decreased by 22 and 32% respectively, as compared to samples treated at 25.degree.C. When lactose was present without calcium during heating, the corresponding decreases in calcium-binding were 17 and 26%, respectively. Similarly, on heating the mixed protein solution at 80 or 95.degree.C without calcium or lactose, the calcium binding measured at a 15 mM equilibrium calcium concentration in solution, decreased by 16 and 25%, respectively, compared to samples treated at 25.degree.C. However, when calcium was present without lactose upon heating at 80 and 95.degree.C the calcium-binding increased by 17 or 13%, respectively, as compared to that of samples heated without calcium. The presence of lactose on heating resulted in a reduction of figures to 8.9 and 0.8%, respectively, as compared to those of samples heated with lactose alone. These results suggest interactions between .alpha.s1-casein and .beta.-lg upon heating. Electrostatic interactions of ionized groups of opposite charge including calcium-binding centres are most probably involved. The .alpha.s1-casein/.beta.-lg complex formed is disrupted during electrophoresis. The calcium-binding figures suggest also the formation of some type of association between .beta.-casein and .beta.-lg.