Changes of secondary structure and protein interactions of whey protein (WPs) present in native, sweet, acid and salty-WPCs were analyzed following storage at 4, 25 or 45 degrees C and 22 or 33% relative humidity for a period of 90-days. WPs aggregated predominantly through covalent crosslinking, achieving maximum at 45 degrees C and 33% RH. Greater participation of beta-lactoglobulin in covalent crosslinking was evident in all WPCs, while that of alpha-lactalbumin was significantly (p < 0.05) high in acid-WPC only. Reaction order of beta-LG denaturation in acid and salty-WPCs was approximately 2 while approximately 1 in native and sweet WPCs. Activation energy was significantly (p < 0.05) higher in native and sweet-WPCs, with averages recorded as 97 and 49.8 kJ mol(-1), respectively, than that in acid and salty-WPCs with averages of 27.5 and 33.8 kJ mol(-1), respectively, mainly attributed to inherently high concentrations of lactic acid and salts in these WPCs. (C) 2017 Elsevier Ltd. All rights reserved.