PEF pre-treatment and ultrasound-assisted drying at different temperatures as a stabilizing method for the up-cycling of kiwifruit: Effect on drying kinetics and final quality

Abstract

The drying of food by-products, such as kiwifruit discards and surpluses, constitutes an interesting option as a means of stabilizing them for later use. This study assesses the combined influence of the drying temperature (40–70 °C), pulsed electric field (PEF) pretreatment (0–5000 V) and ultrasound (US; 0–50 W) application during the drying of kiwifruit. The increase in temperature, the use of PEF pretreatment or the US application during drying accelerated the process, but it was the combination of the three which led to the highest values of the effective diffusivity and the mass transfer coefficient. Over the range of different conditions studied, the functional and antioxidant properties of dried kiwifruit were not significantly affected, while the color presented some differences, mainly related to the L* and a* coordinates. Therefore, the combination of temperature, PEF and US allowed the processing time to be shortened without significantly affecting the final quality of kiwifruit. Kiwifruit is one of the most globally popular fruits. Its high moisture content makes its by-products susceptible to chemical and microbiological degradation, so a drying step is needed to prolong its shelf-life and make up-cycling possible. To this end, hot air drying is one of the most widely-used techniques in the food industry, whose main drawback is a large amount of energy consumed. Therefore, there is a need to look for alternatives to reduce its economic and environmental impact and achieve a quality dried product. This study points out the combination of drying temperature, PEF pretreatments and ultrasound-assisted drying for the purposes of shortening the drying process while preserving the quality of the final product. These results, therefore, underline the promising nature of these techniques not only as regards their application in kiwifruit drying but also in the drying of other fruits and vegetables.