Radio frequency assisted with hot air drying protocol and uniformity of in-shell Macadamia nuts

摘要

Radio frequency (RF) assisted with hot air (RFHA) heating holds potential to provide fast drying of agricultural products with acceptable quality. The purpose of this research was to study application of RF energy in dehydration of in-shell Macadamianuts and shorten the lengthy process times needed in conventional hot air drying. A pilot-scale 27.12 MHz and 6 kW RF system was used to determine the operational parameters, the drying curve, heating and drying uniformity and the quality attributes of the processed nuts. The results showed that an electrode gap of 15.5 cm and a hot air temperature of 50°C provided an acceptable heating rate, stable sample temperatures and acceptable heating uniformity, and were used for further drying tests. The drying curves showed an exponential decay and required 360 min to achieve the final moisture content of 0.030 kg water/kg dry solid (3.0% dry basis) in whole nuts in RFHA drying. The drying kinetics of the nuts was described well by logarithmic model. Peroxide value and free fatty acid increased with the drying time for RFHA drying but remained within acceptable range required by the nut industry. The RFHA process shows potential to provide rapid, uniform and quality-acceptable drying technology for the nutindustry.