Influence of Cropping Season on Lipid Content and Fatty Acid Composition of Rice Bran Milled Rice

Abstract

The influence of cropping season on ether-soluble lipid content and fatty acid composition of ether-soluble lipid of rice bran and milled rice as well as that on combined lipid (lipid by acid-hydrolysis after ether extraction) content of milled rice was investigated on six lowland non-glutinous varieties by early, normal, and late season cultures at Chugoku National Agricultural Experiment Station in 1977. The earlier the cropping season, the higher the ether-soluble lipid content of bran and milled rice became. The significant differences of the content among three cropping season cultures on bran and between late and early or normal season cultures on milled rice were revealed. On the other hand, no influene of cropping season was recognized on combined lipid content of milled rice. As to the fatty acid composition, the earlier the cropping season, the more the palmitoleic acid, stearic acid, and oleic acid contents of bran and milled rice, the arachidic acid content of bran, and the myristic acid content of milled rice. On the other hand, the later the cropping season, the more the linoleic acid and linolenic acid contents of bran and milled rice and the palmitic acid content of milled rice became. The significant differences were observed among three cropping season cultures on palmitic acid content of bran and oleic acid content of milled rice and between late and early or normal season cultures on the other fatty acid contents of bran and milled rice. The daily mean temperature during ripening showed significantly positive correlations with ether-soluble lipid content of milled rice and with myristic acid, palmitoleic acid, and oleic acid contents of bran and milled rice and stearic acid and arachidic acid contents of bran and negative correlations with linoleic acid and linolenic acid contents of bran and milled rice. With respect to the main fatty acids of bran and milled rice, negative correlation was shown between oleic acid and linoleic acid contents. From the regression analysis between oleic acid and linoleic acid contents and between daily mean temperature during ripening and both tlle fatty acid contents, it was shown that equal values of both the fatty acid contents were 38.9% on bran and 37.8% on milled rice and that both the fatty acid contents came to equal values at about 2O°C to 21°C on bran and about 23°C to 24°C on milled rice.