Effect of storage conditions on physicochemical and microstructural properties of skim and whole milk powders

This study examined the effects of storage conditions on physicochemical and microstructural characteristics of whole milk powder (WMP) and low-, medium- and high-heat skim milk powder (SMP). Powders were stored at three temperatures (25 °C, 35 °C and 45 °C) and three humidity levels (11%, 44% and 85%) for 21 days. WMP exhibited lower equilibrium moisture content (EMC) than SMP at these storage conditions. SMP and WMP stored at 45 °C had lower EMC and monolayer moisture content than those stored at 25 °C and 35 °C. WMP had lower T_g, crystallinity and caking strength than SMP. At 85% RH, the particles became irregularly shaped, caused by lactose crystallization. Crystallization of lactose and caking of powders became prominent when T_g decreased below the storage temperature. Crystallization of lactose in these powders increased caking strength, Maillard reaction and surface free fat, particularly at high RH (85%) and high temperature (45 °C) conditions.