The volatiles of steamed rice and of the steam used to cook rice were analyzed in order to identify the undesirable odor components of old rice. Cooked rice was prepared with a newly developed superheated steam rice cooking machine shown in Fig.1. Steam during steam-processing was collected as condensation water by using a distillation column attached to the outlet of the machine. Cooked rice prepared with an ordinary pod style rice cooker was used as a reference. Volatile components were extracted from each rice sample using methyl<i> tert</i>-butyl ether (MTBE). To remove the nonvolatile materials, the collected suspension was distilled under reduced pressure using solvent-assisted flavor evaporation (SAFE). Volatile compounds were extracted from the condensation water by MTBE using a separatory funnel. These suspensions were concentrated and analyzed by gas chromatography-mass spectrometry (GC-MS) and gas chromatography-olfactometry (GC-O) equipped with an Agilent DB-WAX column. About 30 volatiles including aldehydes and acids were identified in cooked rice, with additional ones in the steam that were evidently lost during steam processing. From the GC-O analysis, we detected a lot of undesirable odor in the region with column temperatures ranging from 150-190 °C. This suggests that the compounds in this range might be the key odorants in cooked rice responsible for old rice smell. We are now trying to identify the compounds and confirm their existence in cooked rice, to know how these compounds affect flavor.

Analysis of volatile flavor components of steamed rice and identification of key odorants causing old rice smell

251st National Meeting (2016)

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