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Continuous Hot Pressurized Solvent Extraction of 1,1-Diphenyl-2-picrylhydrazyl Free Radical Scavenging Compounds from Taiwan Yams (Dioscorea alata)

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journal contribution
posted on 07.04.2004, 00:00 by Po-Yen Chen, Yu-Xun Tu, Cheng-Tar Wu, Ting-Ting Jong, Chieh-Ming J. Chang
This study investigates a semicontinuous hot pressurized fluid extraction process and the scavenging activity on the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical of the extract from Taiwan yams (Dioscorea alata). Liquid−liquid extractions were preliminarily employed to generate six fractions, initially extracted by ethanol. Then, the aqueous solution of dried crude ethanol extract was sequentially fractionated by hexane, chloroform, ethyl acetate, and n-butanol. The EC50 value was defined as the UV absorption of DPPH concentrations sufficiently decreased to 50% of the original value. It was found that all peel portions have a better effect on scavenging of the DPPH free radical than meat portions, especially for the ethyl acetate partition of the peel portion of Tainung #2 yam. Its EC50 value (14.5 μg mL-1) was even lower than that of ascorbic acid (21.4 μg mL-1). Furthermore, semicontinuous hot pressurized ethanol was superior to hot pressurized water in extracting the compound scavenging the DPPH radical from the Purpurea-Roxb peel. The recovery of four unknown compounds corresponded to the scavenging ratio of DPPH free radical in the hot pressurized ethanol extract. Finally, three-level and four-factor experimental design revealed that ethanol ratio and temperature were the most effective factors in order. Conditions of 80% of aqueous ethanol, 20.0 kg/kg solid ratio, 180 psig (1.342 MPa), and 100 °C were preferred to extract those antioxidants from the yam peel. Keywords: Dioscorea alata; DPPH free radical; hot pressurized water; experimental design