Defatted rice bran was treated with water or aqueous ethanol under subcritical conditions to recover materials with antioxidative activity. The extraction conditions, namely ethanol concentration (10 − 100% (v/v)), temperature (120 − 237℃) and time after attainment of a desired temperature (5 − 60 min), were studied. On the basis of the determinations of total carbohydrate, protein and phenolic contents, yield, DPPH radical scavenging activity, and antioxidative activity against oxidation of bulk linoleic acid, the extraction with 20% (v/v) ethanol at 237℃ for 5 min was concluded to be comparatively more efficient than that by subcritical water at the same extraction temperature for the same length of time.Keywords: defatted rice bran, extraction, subcritical water, antioxidative activity, ethanol *To whom correspondence should be addressed. E-mail: adachi@kais.kyoto-u.ac.jp
IntroductionRice bran (Oryza sativa) is a byproduct from the rice milling or polishing process of brown rice to produce more visually appealing white rice. In Japan, about 0.88 million tons of rice bran are produced every year, which accounts for approximately 10% of the annual rice production of the country. Defatted rice bran finds uses in animal feeds and fertilizers, but still most of it is discarded as an agricultural waste. Despite its considerable contents of several useful substances, this resource has yet to be fully utilized. The dietary fiber from defatted rice bran was found to exhibit higher water-binding, fat-binding, and emulsifying capacities than that from sugar beet (Abdul-Hamid and Luan, 2000). Defatted rice bran also contains phenolic compounds that have antioxidative (Cuvelier et al., 1992;Graf, 1992), ultraviolet absorbing (Castelluccio et al., 1995), and anti-tumor activities (Han et al., 2001). Several extraction methods, namely the extraction by organic solvents such as methanol (Iqbal et al., 2005), ethanol (Kaneda et al., 2004), and acetone (Chung and Woo, 2001) and non-organic solvents such as supercritical carbon dioxide (Kim et al., 1999), have been the subject of study to recover these functional substances. The organic solvent extraction is a time consuming process and the extensive use of organic solvents also causes pollution. Likewise, the treatment with supercritical carbon dioxide involves a great amount of carbon dioxide which is a predominant anthropogenic greenhouse gas. On the contrary, subcritical water treatment provides an environmentally friendly option for effective extraction of functional substances from food and agricultural wastes (Hata et al., 2008;Pourali et al., 2009;Watchararuji et al., 2008;Wiboonsirikul et al., 2007a;2007b).Subcritical water is water at over 100℃ that is compressed to maintain its liquid state below the critical point. The dielectric constant of water decreases from 80 to 27 with heating from room temperature to 250℃, which is similar to that of ethanol under ordinary pressure (Herrero et al., 2006;Miller and Hawthorne, 2000). At high temperatures, the substantially inc...