Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2000
Publication Date: N/A
Interpretive Summary: Recently, research has identified certain plant compounds (isoflavonoids) in soybeans that may provide benefits to human health. Some of these chemical compounds are induced in soybean by attacking pathogenic microbes, and may, in addition to their possible role in human health, be involved in plant defense. Research is being conducted to optimize production of the compounds in the soybean plant. In this study, accumulation of soybean isoflavonoids in soybean seed was studied in the laboratory after inoculation of the seed halves (cotyledons) with several species of the fungus Aspergillus, two of which (A. sojae and A. oryzae) are "food grade" microorganisms used for industrial fermentation processes. Inoculation with the different Aspergillus species induced isoflavonoids in the living cotyledons suggesting that these chemicals are being produced as part of a plant defense mechanism. Although the health effects of several isoflavonoids already present (constitutive) in soybean seed have been wel characterized, the use of fungal species to induce additional chemicals in soybean seeds may aid in the identification of new compounds with potential health benefits.
Technical Abstract: Several isoflavonoids (e.g. coumestrol) produced by soybeans are thought to be phytoestrogens that can provide potential health benefits for humans consuming soy-based food products. Research is being conducted to optimize production of these compounds in the soybean seed to test their potential health effects. In this study, accumulation of isoflavonoids was studied in the laboratory in imbibed soybean seed. Seed were sliced once across the small axis of the cotyledons and inoculated with conidia of different species of Aspergillus, including A. sojae and A. oryzae used in industrial fermentation processes, and A. niger and A. flavus. Inoculation of cotyledons with the different Aspergillus species induced high concentrations of the isoflavonoids, glyceollin and coumestrol in the cotyledon tissues suggesting that these chemicals are being produced in plant defense against fungal attack. Of the four fungi tested, A. sojae stimulated the highest glyceollin production in cotyledons, reaching a pea concentration at day three. The highest coumestrol concentrations were obtained from soybean cotyledons inoculated with A. niger. Although phytoestrogenic effects of coumestrol isolated from soybean seed have been reported, the possible phytoestrogenic role of other fungally-induced isoflavonoids in soybean seed, such as glyceollin, has not been evaluated. Fungal induction of isoflavonoids in soybean may allow identification and testing of new compounds for potential health benefits.