Feasibility of Simultaneous Drying and Blanching Inshell Hazelnuts (Corylus avellana L.) Using Hot Air-Assisted Radio Frequency (HARF) Heating

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 degrees 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 and penetration depth of the ground 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 degrees C). Hazelnut kernels showed higher dielectric constant and loss factor than shells and inshell hazelnuts. Target temperature did not affect heating uniformity for inshell hazelnuts. A 5-min holding time at the target temperature resulted in better heating uniformity and lower POD and PPO activities (27-35% and 40-45% reduction, respectively). This study demonstrated the feasibility of simultaneous rapid drying and blanching of inshell hazelnuts using HARF technology.