Effects of heat treatment on conformation and cell growth activity of alpha-lactalbumin and beta-lactoglobulin from market milk

Heat processes, low temperature for long time (LTLT) pasteurization and ultra-heat treatment (UHT) sterilization, are essential for commercial market milk to improve the shelf life of raw milk and ensure microbial safety. We evaluated the effects of heat experience on the molecular properties of alpha-lactalbumin (alpha-LA) and beta-lactoglobulin (beta-LG) isolated from four types of market milk such as LTLT-A (66 C for 30 min), LTLT-B (65 degrees C for 30 min), UHT-I (130 degrees C for 2 s, indirect heating) and UHT-D (135 C for 2 s, direct heating) samples. We examined molecular conformations using circular dichroism spectrum measurement and cell growth activity using the WST-1 method for the proteins. alpha-LA isolated from each of these four types of market milk displayed no significant structural difference as compared to raw milk alpha-LA, while a-LA of UHT-I only inhibited cell growth of an intestinal epithelial cell line more potently than raw milk alpha-LA. In the case of beta-LG, only the UHT-I sample demonstrated a drastic change in structure, while it did not exhibit any cytotoxicity. We found that cell viability effects of alpha-LA and beta-LG are attributable to the type of UHT; indirect and direct. These findings indicate that the effect of heat treatment on whey proteins should carefully be investigated further.