Induction of the soybean phytoalexins coumestrol and glyceollin by Aspergillus

Several isoflavonoid phytoalexins produced by soybeans are known to be estr ogenic, with potential beneficial health effects in humans. Increased produ ction of phytoalexins by the soybean plant will facilitate research efforts in this area. In this study, phytoalexin induction and accumulation in soy bean cotyledon tissue was observed using four species of Aspergillus: A. so jae, A. oryzae, A. niger, and A. flavus. All four Aspergillus species teste d elicited phytoalexin accumulation in living soybean cotyledons. Results f rom a time course study indicated that maximum concentrations of the phytoa lexin glyceollin, 955 mu g/g fresh weight (fw), occurred at day 3 in soybea n cotyledon tissue inoculated with A. sojae. Other Aspergillus species caus ed an accumulation of glyceollin at significantly lower levels. A maximum c oncentration of coumestrol of 27.2 mu g/g fw was obtained from soybean coty ledons inoculated with A. niger. Soybean phytoalexins induced by food-grade A. sojae and A. oryzae allowed the collection of higher concentrations of phytoalexins for further examination in several in vitro and in vivo biolog ical studies conducted to determine potential estrogenic activities.