Effects of Temperature and Flow Rate on Subcritical-water Extraction from Defatted Rice Bran

Abstract

The effect of the subcritical water treatment along with the combination of static and dynamic modes on the recovery of protein, carbohydrate and phenolic substances from defatted rice bran was investigated at various treatment temperatures of 120, 160, 200 and 250℃ and the flow rates of 0.5, 2.5 and 5 mL/ min. The highest amounts of protein and carbohydrate were recovered at 160℃ and that of the phenolic substances was recovered at 250℃. Around half of the protein and carbohydrate contents were degraded at 200 and 250℃. The various flow rates from 0.5 to 5 mL/min did not significantly affect the contents of the protein, carbohydrate and phenolic substances recovered from the bran. The extract also had a DPPH radical scavenging activity, which depended on the treatment temperature. While the extract obtained at 120℃ at the same flow rate and same amount of water fed to the bran had the lowest radical scavenging activity, the activities in the extracts at 160 − 250℃ were around 3 times higher than that at 120℃ and there was no significant difference among them.Keywords: defatted rice bran, sub-critical water extraction, radical scavenging activity *To whom correspondence should be addressed. E-mail: adachi@kais.kyoto-u.ac.jp IntroductionDefatted rice bran, which has a very low price, is typically used as animal feed or fertilizer for mushroom cultivation. Indeed, the defatted rice bran can increase its value by recovering valuable substances, such as ferulic acid, a substance exhibiting antioxidative and UV-absorbing properties, and tocopherol (Cuvelier et al., 1992;Castelluccio et al., 1995;Packer, 1991). In addition to the ferulic acid, the bran also contains other phenolic substances including p-coumaric, p-hydroxybenzoic, vanillic, protocatechuic, syringic, caffeic and gentisic acids in significant amounts as well as high protein and carbohydrate contents (Pourali et al., 2010;Okai and Higashi-Okai, 2006). These substances, some of which would be bound to bran matrix, can be liberated and recovered from the defatted rice bran by organic solvent, subcritical water, and supercritical carbon dioxide extractions (Wiboonsirikul et al., 2008;Iqbal et al., 2005;Kim et al., 1999).Subcritical water is hot water at the temperature range from 100 to 374℃ under pressurized conditions in order to maintain its liquid state. Regarding its environmental concern and time requirement, the subcritical water treatment is more advantageous than other methods to recover beneficial biomaterials from agricultural products (Iqbal et al., 2005;Kim et al., 1999;Chittapalo and Noomhorm, 2009). The unique properties of the subcritical water include a lower dielectric constant or polarity and higher ion product at higher temperatures. The dielectric constant of hot water at 250℃ is close to those of some organic solvents such as methanol, acetone and ethanol and the concentrations of the hydrogen and hydroxyl ions at this temperature are higher by three orders of magnitude than that in ambient water. Thus, the subcritical water can recove...

Subcritical Water Technology for Enhanced Extraction of Biochemical Compounds fromChlorella vulgaris

“…In brief, low temperature, longer extraction time, and low biomass loading during SWE support high carbohydrate yields. Extraction of carbohydrate gives negative effects because carbohydrate rapidly decomposed when exposed to higher temperatures [30, 31]. Also, biomass loading has an effect on carbohydrate extraction as the yield decreases when the sample is concentrated.…”

Degradation kinetics of some phenolic compounds in subcritical water and radical scavenging activity of their degradation products

“…In recent years, several studies have shown that subcritical water, that is water in the temperature range of 100–374°C under pressure that is high enough to keep it in liquid state, can be used as an extractant for various groups of compounds . The extraction of phenolic compounds from agricultural materials is one of the applications of subcritical water . Some advantages of subcritical water extraction over others conventional organic solvent extraction methods have been demonstrated in these studies, for example it is an environmentally friendly method and has a high efficiency for the extraction of phenolic compounds.…”

“…[1][2][3] The extraction of phenolic compounds from agricultural materials is one of the applications of subcritical water. [4][5][6][7] Some advantages of subcritical water extraction over others conventional organic solvent extraction methods have been demonstrated in these studies, for example it is an environmentally friendly method and has a high efficiency for the extraction of phenolic compounds.…”

Engineering aspects of rate-related processes in food manufacturing

“…120) Static and dynamic modes have also been tested at various treatment temperatures and flow rates in a packed column in order to determine the effect on protein, carbohydrate, and phenolic recovery. 121) Additional extracts were prepared after 5 min of treatment at 230°C in water and 40% (v/v) acetone, after which those substances soluble in acetone were fractionated from both. The antioxidative activities of the extracts and fractions were then tested against DPPH, hydroxyl and peroxyl radicals, and hypochlorite and peroxynitrile ions and were characterized using a 5-axe cobweb chart.…”