Effect of Microwave Reheating on the Quality and Flavor Compounds of Frozen Rice Balls

To investigate the effects of microwave reheating on the quality and flavor components of rice balls, low-field nuclear magnetic resonance (LF-NMR), texture analyzer, X-ray diffractometer (XRD), fourier transform infrared spectroscopy (FTIR), and gas chromatography-ion mobility spectrometry (GC-IMS) were employed to analyze changes in physicochemical properties, microstructure, and volatile compounds under different microwave power levels (140, 280, 420, 560, and 700 W). The results indicated that temperature uniformity varied across different parts of the rice balls as microwave power increased. The most uniform heating was achieved at 420 W, with the lowest temperature uniformity coefficient of 0.013. Microwave reheating also affected water distribution: The free water content decreased in the inner layer but increased in the outer layer. At 560 W, the differences in hardness and chewiness between the inner and outer layers were minimized, with values of 2.92 N and 16.09 mJ, respectively. Compared to frozen rice balls, reheated samples showed increased starch ordering, disruption of B-type crystal structures, and reduced crystallinity. As microwave power increased, the crystallinity of starch in the outer layer increased, while no significant change was observed in the inner layer (P>0.05). Short-range molecular order decreased only at higher power levels. Among all tested conditions, rice balls reheated at 560 W exhibited the smallest difference in flavor concentration between the inner and outer layers. In conclusion, the optimal reheating conditions for frozen rice balls are a microwave power of 560 W and a reheating time of 110 s.