44C-17 |
Interconversions of isoflavones in soybean as affected by storage |
H. J. HOU and K. C. Chang. Dept. of Cereal Science, North Dakota State Univ., IACC, Rm. 376, Fargo, ND 58105 Isoflavones may impart the bitter and chalky taste in soybean food products. Due to their potential health benefits, isoflavones have attracted the attention of researchers. In soybean, there are three types of isoflavones each in four chemical forms, aglycones, glucosides, malonylglucosides, and acetylglucosides. The effects of extraction and processing methods on the retention, distribution, and transformation of isoflavones in soybeans and soy products had been reported. However, the changes in the content and distribution of isoflavones during soybean storage are remained unknown. The objective was to investigate the transformation and conversion of isoflavones in soybean under different storage conditions. Soybeans were stored in condition of 84% RH 30 °C, 57% RH 20 °C, cold (4 °C), and uncontrolled ambient temperature warehouse. The storage period was 9 months for condition of 84% RH and 18 months for other conditions. Isoflavones were extracted by using acetonitrile-HCl-water mixture and analyzed by HPLC with a C18 reverse-phase column. Nine of 12 isoflavones were quantified directly by available commercial standards. For those without pure standards, concentrations were calculated from the standard curves of aglycones and adjusted on the basis of molecular weight. The results showed that inter-conversion between aglycones and b-glucoside conjugates was significant (p<0.001) in condition of 84% RH, 30 °C. The percentage b-glucoside conjugates in total isoflavones decreased from 99% in the beginning to 2% at the end of storage. On the contrary, the aglycone forms increased from 1% to 98%. For the soybeans in 57% RH 20 °C, and warehouse condition, the glucoside forms had an increasing tendency with storage time, but malonylglucoside and acetylglucoside conjugate forms trended to decrease. The isoflavones of soybeans stored at 4 °C had no significant (p>0.05) changes during storage. This study indicated that storage of soybean under various conditions influenced isoflavones distribution
Session 44C, Fruit & Vegetable Products: Chemistry
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