Hybrid microwave with hot air drying of black-gram (Vigna mungo L) nuggets: Drying characteristics, modeling, and process optimization

Black-gram nuggets (BGNs) were dried using combined hot air-microwave drying (CHMD). Drying kinetics, quality characteristics, and optimization of drying parameters of BGN with the variation of microwave power densities (MPD, 1.33-2 W/g) and temperatures (T, 40-70 degrees C) were studied. Moreover, modeling, effective moisture diffusivity, and nutritional content were also investigated. Drying rate raised initially and attained a peak, followed by a falling rate period. Midilli-Kucuk was the best-fitted model to describe trends of CHMD with the highest R-2 and the lowest RMSE, chi(2), and Akaike information criterion value. Effective moisture diffusivity of BGN varied between 1.257 x 10(-7) and 3.602 x 10(-7) m(2)/s. Increasing T and MPD increased yellowness index, cooking time, and effective moisture diffusivity but decreased hardness and drying time of BGN. Optimum MPD and T were obtained at 1.627 W/g and 58.2 degrees C by applying the desirability function. The nutritional content of BGN can be protected using the optimal CHMD system. Practical applications The present BGN drying is an unhygienic, time-consuming, labor-intensive, and weather-dependent process. Therefore, finding a suitable drying method is necessary. The CHMD technique comparison with conventional drying showed a significant reduction in the drying time due to an increase in drying rate, eliminating weather dependency and can obtain hygienic BGN on an industrial scale. The study of the CHMD system is very important for optimizing the parameters and drying the nuggets in a reasonable amount of time to obtain higher production rates while maintaining the desired quality attributes; Selecting the optimum drying conditions to produce a hygienic BGN without losing nutritional quality has importance for industrial and interest to researchers. Modeling this drying process will also help design the drying system on an industrial scale.