Korean J Nutr.  2003 Jan;36(1):32-39.

Effects of Artificial Stomach Fluid and Digestive Enzymes on the Aglycone Isoflavone Contents of Soybean and Black Bean (Rhynchosia Molubilis: Yak-Kong

• Kang SA
• Jang KH
• Cho Y
• Hong K
• Suh JH
• Choue R

Abstract

Phytoestrogens, especially soy-derived isoflavones, are receiving great scrutiny as a food supplement for preventing hormone dependent disease such as postmenopausal osteoporosis. Their beneficial effects are derived from aglycone form of isoflavones, such as daidzein, genistein or glycitein. In contrast to the common usage of soybean, black bean (Rhynchosia Molubilis : Yak-kong) has been used as a supplement for preventing postmenopausal osteoporosis in oriental medicine. To investigate the effects of the saliva, artificial stomach fluid, and digestive enzymes on the conversion of glycosidic isoflavone to aglycone form, soybean and black bean were extracted with 70% methanol and freeze-dried. The recovery yield of methanol extracts of black bean was 14.1% which was higher than that of soybean, 13.5%. In terms of total isoflavones, we routinely obtained larger amount of isoflavones from black bean than those from soybean. By incubating methanol extracts of soybean and black bean with IN HCI for 180 min, the proportions of aglycones relative to the total isoflavone were significantly increased (32.4% and 52.4%, respectively). In vitro conversion, digestive enzymes (beta-glucosidase and alpha-glucosidase) may hydrolyze glycosidic bond of isoflavone more effectively than saliva or artificial stomach fluid did. It seems to say that the activity of beta-glucosidase was higher than those of alpha-glucosidase. The rate of conversion of glucoside form to aglycone form in black bean and soybean was low in physiological condition (pH) tested, although the enzymatic hydrolysis of glucoside was active. These results demonstrated that the composition of aglycone in food may be the important factors in terms of the bioavailability of isoflavones.

Keyword

soybean; black bean (yak-kong); isoflavone; aglycone; in vitro conversion

MeSH Terms

alpha-Glucosidases
beta-Glucosidase
Biological Availability
Dietary Supplements
Female
Genistein
Humans
Hydrolysis
Isoflavones
Medicine, East Asian Traditional
Methanol
Osteoporosis, Postmenopausal
Phytoestrogens
Saliva
Saliva, Artificial
Soybeans*
Stomach*
Genistein
Isoflavones
Methanol
Phytoestrogens
Saliva, Artificial
alpha-Glucosidases
beta-Glucosidase