Properties of Extract Obtained from Defatted Rice Bran by Extraction with Aqueous Ethanol under Subcritical Conditions

Abstract

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...

Characteristics and Antioxidative Activity of the Acetone-Soluble and -Insoluble Fractions of a Defatted Rice Bran Extract Obtained by Using an Aqueous Organic Solvent under Subcritical Conditions

“…Based on our previous studies, 17,18) water, 20% (v/v) aqueous ethanol, and 40% (v/v) and 80% (v/v) aqueous acetone were selected as the extractants for the subcritical extraction. The extraction process was generally similar as that already described when using subcritical water, except that the solvent in the extracting solution was evaporated by an EYELA N-1100 AN rotary evaporator (Tokyo Rikakikai, Tokyo, Japan) before lyophilization.…”

“…Measuring the decrease in air pressure, which resulted from the oxygen consumed during lipid oxidation, enabled both the induction period and the rate constant to be determined. 28) One hundred mL of the sample solution (0.1, 1.0, and 10 mg/mL) was well mixed with 10% (w/v) methyl linoleate in methanol (1.0 mL) in a glass cup (30 mm  15 mm i.d.) and subjected to reduced pressure for 3 h to remove the solvents.…”

“…Likewise, the extract with water itself also showed weaker activity in scavenging the DPPH radical than those obtained with 20% (v/v) ethanol, 40% (v/v) acetone, and 80% (v/v) acetone. The addition of ethanol or acetone during the subcritical treatment improved the DPPH radical scavenging activity of the obtained extracts 17,18) and of their acetone-soluble fractions.Since the acetone-soluble fraction from the extract obtained with 40% (v/v) acetone showed the highest DPPH radical scavenging activity, the properties of the extracts obtained with both water and 40% (v/v) acetone and their acetone-soluble and -insoluble fractions were characterized for comparison. …”

“…[13][14][15][16] The efficiency of subcritical water extraction could be improved by using ethanol or acetone at the appropriate concentration. 17,18) The phenolic substances in rice bran have generally been suggested to contribute to the high antioxidative activity of the extracts, 19,20) and they may be concentrated by an organic solvent treatment assisted by ultrasonication to render them soluble.The objectives of this study were to investigate the effects of subcritical aqueous organic solvents on a defatted rice bran extract, and to determine the characteristics and antioxidative activity of the extract and its solvent-soluble or -insoluble fractions. …”

Properties of Rice Stem Extracts Obtained by Subcritical Water/Ethanol Treatment

“…With these features, water under subcritical conditions can liberate phenolic compounds, which are bonded to the carbohydrate backbone (Bobleter, 1994;Kumar et al, 2010). Chiou et al (2012) reported that a subcritical water/ethanol mixture could more effectively extract protein, carbohydrate, and phenolic compounds from defatted rice bran than subcritical water or ethanol alone. The addition of ethanol enhances extraction efficiency because constituents with different polarities in the extract are obtained by the ethanol and water (Durling et al, 2007;Richter et al, 1996).…”