33F-31 |
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Z. Y. JU, L. R. Howard, and C. R. Brownmiller. Dept. of Food Science, Univ. of Arkansas, 2650 N. Young Ave, Fayetteville, AR 72704 Sub-critical water (SW) extraction is performed above 100oC, but below the supercritical temperature (374oC) of water with sufficient pressure to maintain water in the liquid phase. An important feature of sub-critical water is a reduction in polarity, expressed as dielectric constant with increasing temperature. The reduced polarity of SWE may enable relatively non-polar phenolics to be extracted from plant materials without chemical reagents. In this research we studied the effect of SW and sulfured water (SSW) extraction temperature on isolating phenolics from grape skins and determined how extraction temperature affected antioxidant capacity of the extracts. Extraction of phenolics from grape skin was performed using a Dionex ASE 200 instrument equipped with a solvent controller. Freeze-dried grape skins (0.40g) were mixed with 30 g of sea sand, and then placed into 22 mL extraction cells. Extraction temperatures of 100 to 160oC in 100C increments were tested using water or sulfured water (1400 ppm Na2S2O3) as solvents. Conventional hot water and aqueous 60% methanol extractions (50 oC for 1 hr) were also conducted for comparison. Extracts were analyzed for phenolic acids, hydroxycinnamic acids, flavonols and anthocyanins by HPLC and oxygen radical absorbing capacity (ORAC). Anthocyanins accounted for 90-96% of total phenolics determined by HPLC in all of the extracts. SSW extracts had higher levels of anthocyanins, phenolic acids, total phenolics and ORAC than SW extracts. Optimal SSW and SW extraction temperatures for total anthocyanins and total phenolics were 110oC and 100-120oC, respectively. SW was equally effective as 60% methanol in extracting anthocyanins and total phenolics at 110o C, while SSW extracted higher levels of anthocyanins and total phenolics than 60% methanol at 100-130o C. Our results indicate that it is possible to extract anthocyanins and other phenolics from dried grape skins using SW and SSW, thus avoiding the need for expensive and toxic organic solvents.
Session 33F, Nutraceuticals & Functional Foods: Antioxidants and phytochemical analysis
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