Abstract: This study attempted to overcome technical bottlenecks in the reheating of pre-cooked clay pot rice such as uneven heat distribution and deterioration in texture, taste and flavor by taking advantage of the penetrability and complementarity of high- (2 450 MHz) and low-frequency (915 MHz) microwave. The effect and underlying mechanism of dual-frequency microwave reheating on the quality changes of non-crusted white rice were investigated. The results of mechanical and apparent morphological characterization showed that amylose content decreased by 4.02%, hardness by 3.61%, and chewiness by 2.47% in medium-power dual-frequency microwave reheated white rice (MDFR) compared with medium-power microwave reheated white rice (MMWR). The moisture content of MDFR was 50.89%, which was not significantly different from that of that fresh sample (50.56%). Moreover, the total color difference (ΔE) of MDFR was 1.44, which was superior to that of MMWR (3.41). The findings demonstrated that dual-frequency microwave reheating slowed down the rate of moisture evaporation, reduced the structural damage of white rice caused by rapid dehydration, and effectively minimized the deterioration of pore structure. Starch characteristics analysis indicated that dual-frequency microwave reheating reduced the breakage of starch molecular chains, effectively maintaining the B + V-type crystalline structure and the short-range ordered structure of white rice starch. Principal component analysis (PCA) of electronic nose and electronic tongue data demonstrated that compound dual-frequency microwave reheating suppressed excessive Maillard reaction. This study provides a theoretical foundation for the application of dual-frequency microwave for the development of high-quality frozen pre-prepared foods.

Key words: dual-frequency microwave; reheating; pre-prepared clay pot rice; quality characteristics; flavor