Doctor of Philosophy (PhD)


School of Nutrition and Food Sciences

Document Type



Soy isoflavones distribution in soy cotelydon, coat and germ were determined. The ƒÀ-Glucoside form of isoflavones was the major class of isoflavones in all three soy parts. Soy germ was the richest source of the isoflavones among the three soybean parts. Distribution of the isoflavones in soy cotyledon was different from that in soy coat or germ. As defatted soy flour is a main byproduct in the soy oil refining process, utilizing the low value byproduct as a valuable food antioxidant was investigated in this study. The level of isoflavones in the defatted soy flour extract was 55 mg/g, which was over 100 times higher than in crude oil or gum. Defatted soy flour extract demonstrated the greatest activity in preventing menhaden fish oil oxidation. It could retain over 60% of DHA (docosahexaenoic acid) and 65% of EPA(eicosapentaenoic acid) in the fish oil after heated at 150oC for 30 min, while only 30% of DHA and 37% of EPA were retained in the fish oil with no additive. The defatted soy flour extract also significantly inhibited the generation of rancid volatiles in the fish oil during storage. The antioxidant capability from highest to lowest was defatted flour extract > gum > degummed oil = crude oil. The antioxidant capability of the defatted soy flour extract and the extract treated with heat and the enzyme were evaluated and compared with common synthetic food antioxidants. While EPA and DHA in the control menhaden oil were degraded to below 10 % after 4 days storage at room temperature, 64% EPA and 60% DHA in the menhaden oil mixed with 5% of the enzyme treated extract and 36% EPA and 28% DHA in the oil with 5% of the heated extract still remained. However, the capability of the heated or enzyme treated extract at 5% addition level was not greater compared to the synthetic antioxidants at 0.02% addition level. The thermal stabilities of soy isoflavones were evaluated at temperatures of 100, 150, and 200‹„R. The degradation rate constants increased with increasing heating temperature. The order of thermal stability from low to high was glycitin < genistin < daidzin < glycitein < genistein < daidzein at temperature below 150 ‹C. The energy of activation (Ea) of the six isoflavones was in a range from 15.9 to 37.6 KJ/mol. It indicated that the glucoside isoflavones were more liable than aglycone isoflavones at high temperature.



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Committee Chair

Xu, Zhimin



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