Abstract
The relationship between the flavor and the heating time of rice (Koshihikari and Reimei) was examined by sensory evaluation. The rice was heated in an oil bath as reported previously. Volatile components in the head space vapor (HSV) of cooked rice were investigated by GLC. Further, volatile carbonyl compounds from unhea ted and heated rice were converted into 2, 4-dinitrophenylhydrazone derivatives, which were determined by TLC, UV spectrophotometry and GLC. The relationship between these analyses and sensory evaluation was discussed.
The following results were obtained : after heating the rice for 20 min, volatile components in the HSV were the largest in quantity, but the flavor of rice heated for 30 min was the most desirable in the sensory test. The results of GLC in the HSV indicated the existence of paraffins (C5, 6, 11), n-aldehydes (C2-7), branched aldehydes (C4, 5), n-alcohols (C1-3, 5), acetone, ethanethiol, 3-methyl-l-butanethiol and dimethyl sulfide.
The volatile carbonyl compounds of the rice were identified as follows : n-aldehydes (C1-9), branched aldehydes (C4, 5), 2-ketones (C3, 4, 6), furfural and benzaldehyde.
The quantity of volatile carbonyl compounds of the rice heated in a closed container was about twice as much as the unheated rice and 42.9% of that of the rice heated in an open container moved into distillate. In the sensory test, the flavor of rice heated in an open container was significantly more desirable than that of rice heated in a closed container, because the undesirable volatile components, such as pentanal and hexanal, decreased during cooking in an open container.
