Feasibility of simultaneous drying and blanching inshell hazelnuts (Corylus avellana L.) using hot-air assisted radio frequency heating (HARF)

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Hot-air assisted radio frequency (HARF) heating was used to dry and blanch inshell hazelnuts with high (19%) and low (11%) moisture content (MC) simultaneously. The effects of target temperature (70, 80, and 90 °C) and holding time (0 or 5 min at target temperature) on heating uniformity and inactivation of polyphenol oxidase (PPO) and peroxidase (POD) were investigated. The dielectric properties of kernels, shells, and inshell hazelnuts were measured at 3 MCs (6–22%), 2 frequencies (13.56 and 27.12 MHz), and 7 temperatures (25–95 °C). Hazelnut kernels showed higher dielectric constant and loss factor than that of shells and inshell hazelnuts. Target temperature did not affect heating uniformity for inshell hazelnuts. A 5-min holding time at target temperature resulted in better heating uniformity and lower POD and PPO activities (15–35% and 24–45% reduction, respectively). This study demonstrated the feasibility of simultaneous rapid drying and blanching of inshell hazelnuts using HARF technology.