Microbial Production of Potent Phenolic-Antioxidants Through Solid State Fermentation - Sustainable Biotechnology: Sources of Renewable Energy - page 232

The potential health effects of dietary phytoestrogens has attracted a great
attention due to their protective action against several health disorders such as can-
cer, cardiovascular diseases, brain function disorders, menopausal symptoms and
osteoporosis [12, 15].
Nevertheless, studies have suggested that in order to express their biological
properties, plant lignans have to be converted into mammalian lignans by micro-
bial action (i.e. demethylation and dehydroxylation) [16, 17]. Secoisolariciresinol
diglycoside and matairesinol are two plant lignans that are not estrogenic by
themselves, but are readily converted by the intestinal bacteria to the estrogenic
mammalian lignans enterodiol and enterolactone, respectively [18]. The main phy-
toestrogen members and plant sources of each, as well as their major compound and
corresponding human actives are summarised in Table 1 [14].
Another plant lignan with estrogenic activity, well known for its antioxidant
properties, is nordihydroguaiaretic acid (NDGA) [19]. NDGA (Fig. 3) is originally
from a semi-desert plant called Larrea tridentata , also known as creosote bush,
which grows in the Southwestern United States and Northern Mexico. Larrea tri-
dentata has been used for centuries by North American Indians as a remedy for
several illnesses including inflammatory conditions as well as tumourous growths
[20, 21]. Although NDGA is found in flowers, leaves, green stems and small woody

Ta b l e 1 Phytoestrogens classes: plant sources, major plant compounds, and corresponding human
activities

Major corresponding
(metabolic) active(s) in
human

Phytoestrogen
class Plant sources Major plant compounds

Lignan Flaxseed Secoisolariciresinol Enterodiol/enterolactone

Seed oils Matairesinol Enterolactone

Grains Pinoresinol Enterodiol/enterolactone

Berries Lariciresinol Enterodiol/enterolactone

Green tea Syringaresinol Enterodiol/enterolactone

Isoflavone Soy Genistein/genistin Genistein

Red clover Daidzein/daidzin Daidzein/equol

Lentils Biochanin A/sissotrin Genistein

Legumes Formononetin/ononin Daidzein

Glycitein/glycetin Glycitein

Prunetin Genistein

Coumestan Clovers Coumesterol Coumesterol

Soy sprouts 4'-methoxycoumesterol 4'-methoxycoumesterol

Alfalfa
sprouts

4'-methoxycoumesterol 4'-methoxycoumesterol

Fig. 3 Chemical structure of
NDGA