Keywords: colored rice, diacylglycerols, fatty acid distributions, free fatty acids, phospholipids, triacylglycerols
IntroductionRice (Oryza sativa L.) is one of the staple cereal crops cultivated in the world and feeds more than half of the world's population (Xue et al., 2008). Colored rices, which are found in Japan, are also classified as Oryza sativa L. Rice is primarily processed and consumed as a whole grain. Moreover, rice grain quality is an important economic trait that influences rice production in many rice-producing areas. Although the fat or oil in rice grain is low (i.e., 2 _ 3%) and is concentrated in the germ and bran, it is a key determinant of the processing and cooking quality of rice (Zhou et al., 2002a). For instance, the surface lipid content is thought to be an indication of the degree of milling (Siebenmorgan et al., 2006), an important factor in determining the nutritional value and economic return of the milled rice. The amount of bran remaining on the rice kernel after milling affects rice quality, appearance, and texture, and rice is thus milled to the end-use preferences of different consumers (Perdon, et al., 2001;Saleh and Meullenet, 2007). In addition, rice lipid, which frequently forms complexes with starch granules, was shown to affect starch gelatinization, water availability to starch and rice swelling, and thus influences the eating and cooking qualities of rice (Champagne et al., 1990;Marshall et al., 1990;Tester and Morrison, 1990).Beside dietary consumption, the unique health benefits of rice fat, which includes many unsaturated fatty acids, has drawn much attention (Jennings and Akoh, 2009 (low-density lipoprotein) without affecting the good cholesterol (high-density lipoprotein) in plasma (Kahlon et al., 1992;Sugano and Tsuji, 1997;Wilson et al., 2007). In addition, rice bran oil, which is rich in tocotrienol (Vitamin E), has anti-cancer and antiradiation effects (Sugano and Tsuji, 1997). On the other hand, some reports have shown that the hydrolysis and oxidation of rice fat are responsible for rice aging and deterioration of grain flavor during storage, and low-oil rice cultivars are more suitable for storage (Zhou et al., 2002b). Therefore, it is important to determine the genetic basis of rice fat synthesis in order to further develop both high-oil and low-oil rice cultivars to address different market needs.Many investigations on lipid fractions of rice brans have been published (Przybylski et al., 2009;Jennings and Akoh, 2009).However, to the best of our knowledge, no comparative study between different colored rice bran cultivars has been conducted with respect to the rice milling process. Therefore, the objectives of this study are to compare the lipid components and fatty acid (FA) distribution of several acyl lipids in three colored rice bran cultivars, based on differences in the degree of milling.
Materials and MethodsMaterials Commercially available mature rice seeds used in this study were from three different colored Japanese cultivars: black (Okunomurasa...
