2023 Volume 72 Issue 10.11 Pages 399-405
The flavor volatiles released during the cooking of rice cultivars were analyzed online via resonance-enhanced multiphoton ionization time-of-flight mass spectrometry (REMPI-TOFMS) in real-time. As rice samples, Tanchomochi (glutinous rice) and Ichihomare (nonglutinous rice) were used; the final amount of water added was slightly reduced in the case of Tanchomochi because it has a higher ratio of water absorption. REMPI detected two volatile compounds, indole and 4-vinylphenol, during cooking at a wavelength of 266 nm. Indole was detected at a lower temperature in the case of Tanchomochi. This rice cultivar has lower swelling/gelatinization temperatures, which is considered the reason for the earlier leakage of indole (or its precursor) during the cooking of rice. In addition, the vaporization of indole proceeded even with the addition of a small amount of water during cooking. On the other hand, 4-vinylphenol was detected at the same temperature (a little less than 100 °C) in each sample, which could have been caused by the temperature of thermal decomposition from its precursor. Also, periodical increases and decreases in signals, due to steam repeatedly being released from a hole in the lid of the rice cooker, could be monitored at real-time via REMPI-TOFMS. This method can be used to elucidate the generation mechanism of flavor volatiles during cooking, which offers the possibility of tailoring cooking conditions to the differences in cultivar type and the milling percentage.
