This study aimed to investigate the effect of lactose on the ageing-induced structural changes through a varying lactose content in whey protein powders. In this scope, four powders differing in their lactose content (0.1-16 w/w %) were stored at 40 C-circle and 60 C-circle for up to 3 months and sampled periodically. A small variation in lactose content of WPI powders was found to affect the level of structural and functional changes during powders ageing. At a higher lactose content (2.6 w/w %), proteins were more rapidly lactosylated and aggregated, with a higher rate than the control WPI powder; whereas at a lower content (0.1 w/w %) the rate of lactosylation and aggregation was considerably limited. These results highlighted the great contribution of the Maillard reaction during ageing of WPI,powders. Reducing lactose content in the WPI powders is a promising way to extend their stability among storage. (C) 2016 Elsevier Ltd. All rights reserved.