Drying characteristics and optimization of ultrasound-strengthened cold air drying combined with sequential far-infrared radiation drying on potato

To improve the dehydration rate and product quality of potatoes, a new strategy utilizing ultrasound-strengthened cold air drying combined with sequential far-infrared radiation drying (UCAD-FIRD) was proposed. The results prove that UCAD greatly promotes dehydration speed, and stronger ultrasound power results in higher drying rate. Compared with UCAD process, UCAD-FIRD drastically shortens the required drying time. Potato slices dried by UCAD-FIRD retain more nutrients compared with those dried by UCAD alone, exhibited by lower color variations and a greater rehydration ratio. For example, total phenol content and Vitamin C content rise first and then, decline but still remain at a high level. The Gray Correlation Analysis is applied to obtain the best experimental group as follows: cold air temperature of 15 degrees C, radiation temperature of 140 degrees C, ultrasound power of 60 W. Therefore, the drying strategy of UCAD-FIRD can remarkably accelerate the drying rate and simultaneously improve the product quality. Practical applications Cold air drying (CAD) can well preserve the product quality due to low drying temperature. However, too long dehydration inevitably restricts its application, so some effective auxiliary measures can be applied to promote mass transfer in CAD to improve the dehydration process. In this study, we proposed a UCAD-FIRD drying strategy, in which contact ultrasound strengthening technology was applied in CAD to significantly accelerate the internal mass transfer of early drying process, subsequently, FIRD was applied to replace UCAD at a certain conversion point to further accelerate water removal in latter stage with lower moisture content. The UCAD-FIRD strategy could achieve both shorter dehydration time and better product quality, comparing with single CAD and UCAD. Therefore, UCAD-FIRD is a promising and practical drying strategy for fruits and vegetables which have great internal mass transfer resistance and thermo-sensitivity.