Microwaves are electromagnetic waves of specific frequencies (300 MHz-3000 GHz), whereas ultrasonic is mechanical waves of specific frequencies. Microwave and ultrasonic technology as a new processing method has been widely used in food processing fields. Combined ultrasonic and microwave technology is exploited by researchers as an improvement technique and has been successfully applied in food processing such as thawing, drying, frying, extraction, and sterilization. This paper overviews the principle and characteristics of ultrasonic- and microwave-assisted food processing techniques, particularly their combinations, design of equipment, and their applications in the processing of agricultural products such as thawing, drying, frying, extraction, and sterilization. The combination of ultrasonic and microwave is applied in food processing, where microwave enhances the heating rate, and ultrasonic improves the efficiency of heat and mass transfer. The synergy of the heating effect of microwave and the cavitation effect of ultrasonic improves processing efficiency and damages the cell structure of the material. The degradation of nutrient composition and energy consumption due to the short processing time of combined ultrasonic and microwave technology is decreased. Ultrasonic technology, as an auxiliary means of efficient microwave heating, is pollution-free, highly efficient, and has a wide range of applications in food processing.
Keywords: combined ultrasonic-microwave technology; drying; extraction; frying; liquid food; thawing.
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