Studies on Cereals Part V

Abstract

When stored rice (40•Ž, two months) was cooked, the stale flavor (komai-shu) was clearly detected by sensory test. Direct gas chromatographic analysis of head space vapors over cooked rice showed three main peaks which corresponded to propionaldehyde or acetone, n-valeraldehyde and n-caproaldehyde. On the other hand, the content of linoleic and linolenic acids of the rice decreased during storage at 40•Ž. This means that the unsaturated fatty acids autoxidized during storage and gave rise to carbonyl compounds responsible for the stale flavor of cooked rice.

Cooking Flavor and Texture of Rice Stored under Different Conditions

“…None of these headspace volatiles was evaluated to have the characteristic off-flavor of cooked old rice by GC-sniffing. Table III shows that not only pentanal and hexanal, reported by Yasumatsu et al 3 ) as causal components of the off-flavor of cooked old rice, but also heptanal, alkenals, aromatic aldehydes, ketones, 2-pentylfuran, etc. were found in larger quantities in 40°C-stored rice than in 4°C-stored rice.…”

Changes in Physicochemical Properties of Rice during Storage

“…The oxidation of fat to carbonyl compounds which affect protein properties [2] did not appear to be important in the changes that occur during storage, except for the formation of stale flavor in aged milled rice [31]. Protein denaturation as reflected by the reduction in salt-soluble protein was as high in stored defatted milled rice as in stored milled rice, in spite of the difference in contents of carbonyl compounds.…”

Cooking flavor and texture of rice stored under different conditions.

“…reported that both ether-defatted rice flour and original rice flour showed the same amylograms after storage.5) From these results, they concluded that the changes to old rice were not caused by the interaction between lipid and starch but caused by other qualitative and/or quantitative changes in the rice grain during storage. Yajima et al6) have identified many other volatile components, which had not been reported by Yasumatsu et al,3) in the steamdistillate of cooked rice. Tsugita et al7) have reported 40 volatile components in the headspace vapor of cooked rice milled to different degrees.…”