Changes in isoflavone profiles of soybean treated with gamma irradiation.

Soybean is an important Brazilian agricultural commodity that contains a high concentration of isoflavones. Many studies showed that isoflavones are active in the prevention of many human diseases. However, the correct processing techniques used to prepare the soy foodstuffs are important to maintain the active forms. The objective of this study was to evaluate the effect of gamma irradiation on the isoflavone contents of the defatted soybean flour when compared with soybean molasses, a derivative from the soybean food production. After extracting phenolic compounds with methanol aqueous solution (80%), isoflavones were detected by reverse-phase high-performance liquid chromatography/diode-array detector. The radiation doses of 2 and 5 kGy presented a small effect on the isoflavones content of defatted soy flour. Samples irradiated at 50 kGy showed lower isoflavone contents. The observed reduction in the concentration of isoflavones-daidzein, glycitein and genistein-induced by gamma radiation in soy molasses was not significant in defatted soy flour, thus suggesting that isoflavones in defatted soy flour were not eliminated by gamma radiation at rates up to 50 kGy.

Effects of riboflavin photosensitization on daidzein and its photosensitized derivatives.

Photosensitized compounds from daidzein were studied in a riboflavin model system under visible light irradiation by high-performance liquid chromatography (HPLC). As the period of light irradiation increased, concentration of daidzein decreased significantly (P < 0.05) and new peaks of daidzein derivatives were observed and changed during photosensitization. Three new peaks from photosensitized daidzein were tentatively identified as 7-, 3', 4'-trihydroxyisoflavone (or 3'-hydroxydaidzein) and 2 dimmers of daidzein by a combination of HPLC-mass spectrometry (MS) and retention times of standard compounds by HPLC. Addition of sodium azide and removal of headspace oxygen treatment affected the formation of newly formed peaks. The type I pathway of riboflavin photosensitization played more important roles than type II pathways on the formation of daidzein derivatives. Practical Application: Isoflavones are important phytochemicals found in soy foods. Generally, many foods containing soy ingredients are displayed under visible light irradiation. Also, riboflavin can be found in many foods containing vegetables. The results of this study can be used to understand the stability and changes of isoflavone aglycones in soy and soy-based foods under visible light irradiation.