Changes in physicochemical properties of spray-dried camel milk powder over accelerated storage

Changes in physiochemical properties of spray-dried camel milk powders during storage at 11-32% RH and 37 °C over 18 weeks were investigated. The results showed that fresh camel milk powders had amorphous structure, clumsy spherical shape particles and almost 100% solubility in water. During storage at controlled low RH levels (<32% RH), reduction in moisture content and a_w of the powders caused glass transition signals of lactose to evolve, although the powders exhibited a slight development of crystallinity. True density, colour (L*, a* and whiteness), and morphology were almost unchanged during storage while b* values associated with non-enzymatic browning, and fat oxidation into volatile compounds increased steadily. Over storage period, solubility of the powder declined just slightly and secondary structure of proteins unfolded from α-helices to β-sheets, loops and β-turns. These changes were more profound for the powders stored at 32% RH than those kept at 11 and 22% RH.