Preconditioning of rice is heat curing of salt infused moist parboiled rice prior to microwave puffing process. The sudden expansion of moisture present in the interstices of the starch granules caused by microwave heating of the preconditioned rice results in highly expanded smooth‐surface puffed rice. The expansion ratio (ER) and percentage of puffing (PP) of the microwave puffed rice preconditioned under different conditions were varied between 5.16–7.51 and 84.32–93.12%, respectively. Optimum temperature, air velocity, and salt concentration for fluidized bed preconditioning obtained by using integrated artificial neural network and genetic algorithm approach were estimated to be 70°C, 2.9 m s−1, and 4%, respectively. The predicted values of ER and PP at optimum combination of independent variables were 7.5 and 92.82%, respectively. Scanning electron microscopy revealed that preconditioning transformed the compact polyhedral structure of starch granules to fused mass with interlocking and overlapping structure.
Practical applications
Preconditioning with fluidized bed drying of salt infused rice would be feasible as a substitute with traditional direct heat curing process with saving of time, labor, and energy. This study would enhance understanding of the effects of preconditioning process on the mechanisms of puffing. Artificial neural network and genetic algorithm integrated optimization can be applied for prediction and control of mechanization of the preconditioning and puffing process. Preconditioned rice can be puffed directly by using a microwave oven that will make the puffing process convenient to consumers.
The purpose of this study was to develop a predictive three‐dimensional analytical model for predicting the temperature profile during microwave and convective drying of dragon fruit. A combined electromagnetic (Maxwell's equation) and heat transfer model was used for modeling of microwave drying. This heat transfer modeling is applicable to describe the thermal dissipation during the microwave and convective drying of agricultural produces. In this process, the dragon fruit cube of 15 mm was dried at a microwave power of 200, 400, and 600 W during the microwave drying process and hot air temperature of 60°C during the convective drying process. During microwave drying, the core or center temperature was maximum compared with the temperature at the surface of the dragon fruit cube. The predicted temperature at the center of the dragon fruit cube exposed to the microwave power of 200, 400, and 600 W for 60 s of drying time was 34.67, 44.34, and 54.02°C, respectively. In convective drying, the temperature at the edges was higher than the temperature at the center point of the dragon fruit cube. During convective drying, the fruit sample attained the maximum temperature of 60°C after being exposed to hot air for 8 min. The RMSE and χ2 values between experimental and model projected values were less than 0.988 and 0.029 in microwave drying and less than 0.891 and 0.018 in convective drying, indicating that the model projected values were in good agreement with the experimental values.
Practical Applications
The importance of thermal processes in deciding the safety and quality of food products is emergent. This model can predict food product temperature distribution during the hot air drying and microwave drying of Dragon fruit cubes. The economy of the drying process is often influenced by the nature and operation of these processes and hence modeling of the drying process is a crucial factor for the industry. These results can be used to quantify heat and moisture distribution, as well as to monitor the drying process of fruits and vegetables, saving energy and time.
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