Use of ultrasound and ethanol to improve the drying of yacon potato (Smallanthus sonchifolius): Effect of chemical and thermal bleaching

Yacon is a prebiotic food, rich in insoluble fibers, however, highly perishable because of its high moisture content and unstable coloration after peeling, due to enzymatic browning. To overcome such challenges, this study evaluated the effects of two types of bleaching (chemical and thermal) to precede the pretreatment with ultrasound (US) and ethanol, to study the influence of these methods on drying kinetics, and on changes in product color. Yacon cylinders were dried in a tray oven at 50 °C and it was found that the drying time until final moisture content was reduced after the application of pretreatments. Particularly, pretreatment with ethanol combined with ultrasound provided the greatest reduction in drying time to reach 25% moisture content for both the chemically bleached vegetable (30.1% reduction), and the thermally bleached vegetable (61.2% reduction). The best drying rate was observed for pretreatment with US, yet the water which permeated into the internal matrix during this pretreatment likely limited great reduction in drying time. Regarding product color, chemical bleaching was more efficient in preserving the color characteristics of the product. These results show new perspectives regarding the use of ethanol and ultrasound associated with different pretreatments to improve the convective drying of yacon. •Ethanol + US provided the greatest reduction in drying time.•Chemical bleaching was more efficient in reducing drying time.•Pre-treatment with US resulted in a higher drying rate.•Chemical bleaching promoted less interference in color.