Kinetic Modeling of Mass Transfer During Roasting of Soybeans Using Combined Infrared-Hot Air Heating

Roasting is one of the widespread methods for processing of nuts and beans that significantly enhances the flavor, color, texture and appearance of the products. In this research the kinetics and modeling of soybean roasting using combined infrared-hot air system and consumption of energy were investigated. The effect of the hot air temperature (160, 180 and 200 ºC), infrared powers (200, 250 and 300 W) and combined hot air temperature and IR powers (120, 140 and 160 ºC- 130, 165 and 200 W) on roasting rate of soybeans were evaluated. The results showed that the effect of hot air temperature, infrared power and combined hot air temperature and IR power on the roasting rate of soybean were statistically significant and the roasting process occurred within the falling rate period. Among the five thin-layer roasting models fitted to the experimental data, the page model was the best to describe the roasting behavior. Fick’s law of diffusion was used to determine the effective moisture diffusivity, which varied between 1.727×10-9 to 4.518×10-9 m2/s. Activation energy was estimated by Arrhenius and modified Arrhenius equations as 22.0234 kJ/mol and 4.3778 kW/kg, respectively. Comparison of roasting methods showed that minimum energy was consumed in the infrared method (0.0905 kWh) and maximum energy was recorded for hot air roasting (1.752 kWh), thus infrared radiation could be considered as a promising technique for roasting of soybeans due to lower energy cost.