Assessment of anticaking agent on caking behavior of jujube amorphous powder via glass transition and state diagram

Jujube (Ziziphus jujuba Mill.) powder is hygroscopic and highly prone to caking during storage which could significantly reduce product quality. Anticaking agents are usually added to maintain flowability of powders and prevent caking. Caking behaviors of jujube powder and blends with anticaking agents (calcium stearate, magnesium stearate, and silicon dioxide at 1, 2, 3% w/w) as affected by temperature (25\ua0°C, 35\ua0°C, 45\ua0°C), mixing speed (22, 73, 96\ua0rpm), and mixing time (1, 5, 10, 15, 20\ua0min at 25\ua0°C) of powders exposed at 75% RH for 5\ua0h were investigated by FT4 powder rheometer. Energy of crust that formed during caking was determined. Results showed that anticaking agents resulted in significant effect on the moisture sorption and crust strength formed during caking of jujube powders. Calcium stearate (2% w/w) proved to be the most effective to improve the flowability and delay onset of powder caking with significant reduction in the crust strength of powder cake from 170 to 2\ua0mJ/g when powders exposed to 75% RH for 5\ua0h at 25\ua0°C. Mixing speed at 73\ua0rpm and mixing time of 5~20\ua0min could present better flowability of jujube powders and delay the onset of caking. Lower (22\ua0rpm) and higher (96\ua0rpm) mixing speeds and higher temperatures (45\ua0°C) could speed up caking rate in powder blends. State diagrams established based on moisture sorption isotherm and glass transition curves showed that jujube powders with and without calcium stearate addition were stable at 25\ua0°C when water content was lower than 0.095 and 0.088\ua0g water/g sample, respectively