17D-6 |
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K.-W. LIN, Dept. of Food & Nutrition, Providence Univ., 200 Chungchi Rd., Shalu, Taichung County, 433, Taiwan and Y.-T. Chen, Dept. Food and Nutrition, Providence University, 200 Chungchi Road, Shalu, Taichung County, Taiwan. Yam (Dioscorea spp.) is a typical agriculture produce and has been found to possess particular biochemical and physiological functions. Dioscorin is the most abundant storage protein of yam and shows trypsin inhibitor and possible antioxidative activity. However, the functionalities of yam vary with species and stability of dioscorin at various cooking temperatures are not yet elucidated. Our objectives were to evaluate the antioxidative ability of various yams and the stability of purified dioscorin affected by cooking temperature. Three varieties of yam were assigned to various water cooking temperatures. Yams were blended with buffer and crude yam extract was fractionated followed by ion-exchange and gel permeation chromatography. Collected protein was electrophoresized for molecular weight determination. Total phenolic content and antioxidative ability of yams were determined. Protein surface hydrophobicity of dioscorin was performed. Each determination was run in triplicate and the entire procedure was replicated three times. A 3 (variety) x 7 (cooking temperature + raw) factorial design of GLM was performed and the Duncan's Multiple Range Test was used for comparison when main effects were different. Crude yam extract of all varieties showed decreasing total phenolic and dioscorin contents, DPPH radical scavenging activity and ferrous ion chelating capacity with increasing cooking temperatures. Ming-Chien yam had the highest DPPH radical scavenging activity in raw and at various cooking temperatures, but Keelung yam had virtually no ferrous ion chelating effect. Dioscorin of all varieties had a similar molecular weight of 31 kDa, but could not be extracted above 80 ¢X C. Protein surface hydrophobicity of dioscorin from all species decreased with increasing cooking temperatures indicating more severe protein denaturation occurred to protein molecules. Results indicate the instability of dioscorin at temperature above 80 ¢X C, and significant influences of heating temperature on yam's functionalities. Ming-Chien yam appears to have better antioxidative ability than other varieties.
Session 17D, Food Chemistry: Chemical effects of food processing and preservation
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