Effects of Ultrasound on Mass Transfer Kinetics,Structure, Carotenoid and Vitamin C Content of Osmodehydrated Sweet Potato (Ipomea Batatas)

The effects of ultrasound pretreatments on mass transfer kinetics, microstructure, carotenoid and vitamin C contents of sweet potato were investigated. Sweet potato samples were treated in distilled water with ultrasound (DWU), osmotic dehydration without ultrasound (OD) and ultrasound-assisted osmotic dehydration (UOD). Samples were subjected to ultrasound probe of 2 cm diameter, frequency of 28 kHz at 300 W maximum power at different pretreatment times of 20, 30, 45 and 60 min. The Azuara model used in this study fitted the experimental data well with high coefficient of correlation ranging from 0.92 to 0.98, low values of chi-square (<0.6), root mean square error (<0.9) and percent mean relative deviation (<10%). The results showed that UOD significantly (p < 0.05) had the highest mass transfer coefficient and equilibrium value for water loss and solid gain, compared to DWU and OD. DWU had no significant effect on the structure of sweet potato samples, while UOD had the highest effect on the structure. The samples treated in OD had the highest carotenoid retention compared to DWU and UOD at all pretreatment times. However, ultrasound enhanced the retention of vitamin C (>70%) in sweet potato samples treated in DWU and UOD.