Internal and External Color Development Kinetics during Microwave Assisted Fluidized Bed Drying of Hazelnut

Microwave assisted fluidized bed drying is a novel drying technique which reduces drying time and yields higher quality products. In this study the effect of this method on color changes of whole and cut hazelnut kernels was investigated. The parameters of color and resulting total color change, chroma, Hue angle and browning index were also calculated during drying in three temperatures (۴۰, ۵۰ and ۶۰°C) and microwave power levels (۰, ۴۵۰ and ۹۰۰W). Comparison was made to investigate the effect of drying condition on browning of hazelnut surface and internal cavity. The zero and first order kinetic models were also fitted to whole and cut kernel color parameters. The results showed similar behavior in color parameters of whole and cut kernels. L value and Hue angle decreased with increasing drying time, drying air temperature and microwave power but a, b, ΔE, chroma and browning index increased. L and b values of whole kernels were higher than cut kernels but the a value was lower. Zero-order model was selected as the best model for predicting a, b and ΔE while first order model best described the kinetics of color changes of L, chroma, Hue angle and browning index.