Heating uniformity improvement of the intermittent microwave drying for carrot with simulations and experiments.

Heating uniformity is always a concern in microwave drying for foodstuff, where unsatisfied product quality could be caused by over‐ or inadequate‐heating. To deal with this concern, multi‐physics field rotation simulation models and intermittent microwave drying modes were designed and evaluated in this study. Four drying modes with different intermittent time ratios (R1/2, R1/3, R1/4, and R1/5) were first applied in drying experiments. Their effects on temperature distribution, drying characteristics, and quality aspects (chromatic aberration, rehydration ratio, vitamin C content, and sensory evaluation) for carrot samples were compared and analyzed. The results revealed that the carrot quality in R1/4 mode drying was increased by up to 64% in comparison with the other three modes. The root‐mean‐square error of the moisture ratio was maintained at a lower value, and a better consistency was also achieved in R1/4 mode. To further improve the drying performance and efficiency, a novel stage intermittent‐time control strategy was attempted, that is, an appropriate strategy was used in each drying stage. With this method, the best drying effect could be obtained. The above work can promote a deeper understanding of the drying kinetic and provide novel operation strategies in the microwave drying of food products. Practical applications: A multi‐physics field rotational simulation model (MFRSM) coupled with an intermittent microwave drying process, including electromagnetic heating, heat, and mass transfer, was developed to characterize the drying process of rotating samples in an intermittent microwave dryer. The MFRSM was helpful to analyze the continuous microwave drying process of the sample and deepen the understanding of the internal heat and mass transfer process of the sample. Four modes with different intermittent schedules were designed, and simulation models were also established. The drying characteristics in different modes were analyzed; a long intermittent time could affect the drying efficiency on account of the driving force, while a short intermittent time would reduce the product quality because of the continuous high temperature. R1/4 mode was founded in terms of drying efficiency and drying quality. An optimized stage intermittent‐time control strategy (R‐IO mode) was designed. The drying time in the three stages was shortened by 25% in total compared with R1/4 mode. Meanwhile, the vitamin C retention, the taste quality of the dried products were improved. These works are expected to provide benefits for the understanding of the intermittent microwave drying modes on drying kinetic using the MFRSM. It can also be useful in the development of an IMD for food materials. [ABSTRACT FROM AUTHOR]

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