Hot-air assisted continuous radio frequency heating for improving drying efficiency and retaining quality of inshell hazelnuts (Corylus avellana L. cv. Barcelona)

Abstract

Hot-air assisted continuous radio frequency (HARF) heating was utilized to dry inshell hazelnuts to achieve rapid heating and better retention of nut quality. Effect of electrode gap (14, 15, and 16 cm) and hot-air (HA) temperature (30, 40, and 50 °C) on HARF drying efficiency and heating uniformity was investigated. Electrode gap of 14 cm and HA temperature of 40 °C were identified as optimal HARF conditions to provide acceptable heating rate (4.24 °C/min), heating uniformity (0.16), and heating efficiency (19.18%) along with short drying time (22 min). Compared to HA drying, HARF provided much higher drying rate and effective mass transfer coefficient with lower energy consumption. Besides, HARF dried nuts had higher total phenolic content (0.43 mg GAE/g dry kernel), lower peroxide value (undetectable) and polyphenol oxidase activity (15.42 μkat/L) than that of HA dried ones, indicating HARF being a technology having great potential for drying hazelnuts.