Analysis of Volatile Odor Components of Superheated Steam-cooked Rice with a Less Stale Flavor

Milled common Japonica rice was cooked using a newly developed superheated steam rice cooking machine and the volatile odor compounds of the steamed rice and of the steam generated during cooking were analyzed. At least 22 odorous compounds were found in the steam by GC-olfactometry, of which 13 were identified by GC-MS. Hexanal and (E,E)-2,4-decadienal, which are known odor compounds characteristic of cooked rice, were identified, and four compounds, including longifolene and 2-methoxyphenol, were newly identified in Japonica rice. The amounts of hexanal and (E,E)-2,4-decadienal in steamed rice, extracted with methyl tert-butyl ether, were essentially the same as in ordinary cooked rice. On the other hand, headspace analysis showed that the levels of odor compounds in steamed rice were less than 10% that of ordinary cooked rice. Only small amounts of odorants appear to be released from the surfaces of steamed rice grains.