Influence of ultrasound pretreatments on diffusion coefficients, texture and colour of osmodehydrated sweet potato ( Ipomea batatas )

The moisture and solute diffusivities, texture and colour of sweet potato pretreated in distilled water with ultrasound ( UD ), osmotic dehydration without ultrasound ( OD ) and osmotic dehydration with ultrasound ( UOD ) were investigated to determine the effects of ultrasound on osmodehydrated sweet potato. The moisture and solute diffusivities of all the pretreatments ranged from 2.89 to 4.95 × 10 −10 and 1.17 to 1.67 × 10 −10  m 2  s −1 , respectively. The moisture diffusivity of samples treated in UOD was significantly ( P  < 0.05) higher than that of OD and UD by 30.82% and 41.62%, respectively. Compared to the fresh sample, the firmness of samples treated in OD and UOD was reduced by 83.53% and 92.47%, respectively. UD increased the brightness (L*) and reduced the redness (a*) of sweet potato, while UOD enhanced the yellowness (b*) and chroma (C*) of sweet potato. The sweet potato samples treated in UOD had the highest total colour difference (Δ E ).