Evaluation of some thermodynamic and physical properties of garlic different thickness under drying by microwave method with ultrasonic pretreatment

Garlic has many medicinal properties in the food industry. In this study was investigated the effect of ultrasonic pretreatment (10, 20 and 30 min) on some thermodynamic and physical properties of dried garlic at thicknesses (2, 4 and 6 mm) using microwave at different power (100, 200 and 300 W). 10 mathematical models were used to describe the moisture ratio during garlic drying. The obtained results from this investigation showed that specific energy consumption (SEC) decreased significantely (p < 0.05) with increasing ultrasonic time, microwave power as well as with decreasing the thickness of samples. Fitting the mathematical models to the moisture ratios with the experimental data showed that the Logistic model can satisfactorily satisfy the drying curve of the samples in a microwave dryer with ultrasonic pretreatment with high correlation coefficient (R2 = 0.9996), minimum root mean square error (RMSE = 0.0113), and chi-square (χ2 = 0.0009) to describe. Effective moisture diffusion coefficient of the dried samples was found to be 8.04×10-11 to 1.64×10-9 m2/ s. The highest and lowest SEC was 340 and 35.87 kWh/kg, respectively. The results showed that increasing the microwave power, ultrasonic time, and decreasing thickness of the samples reduced significantely (p < 0.05) the shrinkage. By decreasing the microwave power and thickness of the samples as well as increasing the ultrausonic time, reduced significantely (p < 0.05) the color value.