Define the Dietary Sources and Chemical Forms?
Isoflavones and coumestans are the most common compounds. Soybeans and soyfoods are the most important sources, containing approx. 0.2-1.6 mg per gram dry weight; although chick peas and other legumes also contain them. Second generation soy foods e.g., products like tofu yoghurt contain 6-20% of the isoflavones present in the whole beans. Isoflavones may be present in unconjugated form (aglycones) e.g. daidzein, genistein, or as glycosides such as daidzin, genistin.
Non-fermented soy foods like tofu contain greater levels of glucosides whereas fermented foods e.g. tempeh have higher amounts of aglycones due to enzymatic hydrolysis during the fermentation process. A large number of cournestans e.g. coumestrol in alfalfa have been isolated from plants but only a few possess uterotropic (stimulating growth of the uterus) activity. The highest amounts of coumestans are present in clover and alfalfa sprouts (5.6 and 0.7 mg/g dry weight). Other sources are split peas, kala chana, lima beans and soy bean sprouts (15-80 mcg/g dry weight). Lignans do not induce estrus but are considered to be phytoestrogens because they have oestrogen-like actions. They are present in plant foods and human biological fluids, plant lignans being converted by bacterial action to mammalian lignans in the GIT. Secoisolariciresinol and rnatairesinol are plant dietary precursors of the mammalian lignans, enterodiol and enterolactone.