Morphological and mechanical properties of dried skimmed milk and wheat flour mixtures during storage

Five mixtures of dried skimmed milk (DSM) and wheat flour (WF) were prepared and stored for 45 days at 20 °C and various relative humidities (RH) from 0% to 85%. Morphological properties, particle size distributions and mechanical properties were studied before and during storage. Scanning electronic microscopy (SEM) showed that samples stored at high RH (59–85%) agglomerated and formed a compact mass of powder due to caking phenomenon. The caking intensity increased with storage relative humidity and was expressed as the maximum force (Fmax.) calculated from force/compression curves. DSM powders showed stick-slip behaviour during deformation and, moreover, this phenomenon increased with the DSM ratio in the mixture (up to 20 ± 1 N for 100% DSM) and disappeared with storage relative humidity.