Determination of bulk density of Mirabelle plum during hot air drying as influenced by ultrasound-osmotic pretreatment

Prunes are generally produced by drying fresh plums with a stream of hot air. Changes in various quality indicators, such as bulk density of foodstuffs, have substantial impact on the performance of drying processes. Optimization of bulk density is, therefore, a requirement for development and perpetuity of drying technologies. The aim of this study was to investigate the effect of ultrasound-assisted osmotic dehydration pretreatment on bulk density of Mirabelle plum at various operating conditions (sonication time, concentration of osmotic solution and immersion time in the osmotic solution). Results showed that application of ultrasound-assisted osmotic dehydration, compared to control sample, led to a significant (p < 0.05) increase in bulk density from 1.33 to 9.90 %. Experimental data of bulk density variations versus dimensionless moisture content were well fitted to an empirical power model with high R2.