Hiroyuki Tanimoto

Higher bioavailability of isoflavones after a single ingestion of aglycone‐rich fermented soybeans compared with glucoside‐rich non‐fermented soybeans in Japanese postmenopausal women

BACKGROUND There have been conflicting study results concerning how the food matrix affects the bioavailability of isoflavone aglycone and glucoside. In this study the bioavailability of isoflavones after a single ingestion of aglycone-rich fermented soybeans (Fsoy) and glucoside-rich non-fermented soybeans (Soy) was compared. Eleven healthy postmenopausal Japanese women were recruited for a randomised, double-blind, crossover trial and consumed Fsoy or Soy powder dissolved in hot water. Blood samples were collected 0, 1, 2, 3, 4, 6, 8, 12 and 24 h and urine samples from 0 to 48 h after ingestion of the powders. The Fsoy and Soy powders ingested had the same total isoflavone content (95 µmol), but the former was rich in aglycone (90.6 µmol) while the latter was rich in glucoside (81.9 µmol). RESULTS Serum concentrations of total isoflavones after 1-4 h were significantly higher in the Fsoy group than in the Soy group. The Fsoy group showed significantly higher maximum concentration (Cmax: 2.79 ± 0.13 vs 1.74 ± 0.13 µmol L(-1) ) and area under the curve (AUC(0-24 h) : 23.78 ± 2.41 vs 19.95 ± 2.03 µmol day L(-1) ) and lower maximum concentration time (Tmax: 1.00 ± 0.00 vs 5.00 ± 0.67 h) compared with the Soy group. The cumulative urinary excretion of total isoflavones after 2 h was significantly higher in the Fsoy group than in the Soy group. Individual isoflavones (daidzein, genistein and glycitein) showed similar trends to total isoflavones. Equol (a metabolite from daidzein) did not differ between the two groups. CONCLUSION The results of this study demonstrated that the isoflavones of aglycone-rich Fsoy were absorbed faster and in greater amounts than those of glucoside-rich Soy in postmenopausal Japanese women.

Acute Effect of Poly-γ-Glutamic Acid on Calcium Absorption in Post-Menopausal Women

Objective: Poly-γ-glutamic acid (PGA) increases calcium (Ca) solubility in vitro and in vivo, and is associated with reduced bone loss in post-menopausal Japanese women. This study is the first to examine the effect of PGA on Ca absorption in humans. Methods: A single-blind, randomized, crossover study with a 3–4 week wash-out was performed to determine the effect of PGA (80.6% glutamic acids) on Ca absorption measured by the double stable isotope method. Twenty-four healthy, non-smoking, postmenopausal women (mean age: 56.4 ± SE 0.9) were given 200 g of orange juice containing 200 mg Ca as Ca-44 enriched CaCO3, with or without 60 mg of PGA, after an overnight fast. The two tests were separated by 3–4 weeks. An intravenous injection of Ca-42 (CaCl2 solution) was given 30 min after consuming the drink and a complete urine collection carried out from 24–48 h post-dosing. Ca absorption was calculated from the Ca isotope ratios measured by thermal ionization quadrupole mass spectrometry (TIQMS). Results: Mean Ca absorption with PGA was significantly higher (P < 0.01) than without PGA, 39.1 (SE 1.6) % and 34.6 (SE 1.9) %, respectively. The effect of PGA on increasing Ca absorption was more marked in a sub-group of subjects whose baseline Ca absorption (without PGA) was lower than the population mean value. Conclusion: Postmenopausal women who received a single dose of PGA increased their intestinal Ca absorption particularly those individuals with lower basal absorptive capacity.

Characterization of γ-Glutamyl Hydrolase Produced by Bacillus sp. Isolated from Thai Thua-nao

γ-Glutamyl hydrolase with a molecular mass of 28 kDa was purified from the culture broth of Bacillus sp. isolated from Thai Thua-nao, a natto-like fermented soybean food. The purified enzyme hydrolyzed chemically synthesized oligo-γ-L-glutamates but not oligo-γ-D-glutamates and degraded γ-polyglutamic acid to a hydrolyzed product of only about 20 kDa (with D- and L-glutamic acid in a ratio of 70:30), suggesting that the enzyme is a γ-glutamyl hydrolase that cleaves the γ-glutamyl linkage between L- and L-glutamic acid of γ-polyglutamic acid.

Structure of the Hydrolyzed Product (F-2) Released from γ-Polyglutamic Acid by γ-Glutamyl Hydrolase YwtD of Bacillus subtilis

The structure of the hydrolyzed product (F-2) with a molecular mass of about 2 kDa released from γ-polyglutamic acid by the γ-glutamyl hydrolase YwtD of Bacillus subtilis was analyzed. The results showed that F-2 is an optically heterogeneous polymer consisting of D- and L-glutamic acid in an 80:20 ratio with D-glutamic acid on both the N- and C-terminal sides, suggesting that YwtD is an enzyme that cleaves the γ-glutamyl bond between D- and D-glutamic acid recognizing adjacent L-glutamic acid toward the N-terminal region.

Food Applications of Poly-Gamma-Glutamic Acid

Poly-γ-glutamic acid (γ-PGA) is a unique polymer in which both d- and l-glutamic acids are combined with γ-linkages. γ-PGA is safe, water soluble, anionic, and edible substance, which has many features such as high water absorbability, viscosity, metal-binding property, less susceptible for intestinal enzymes, and tasteless, etc. and the production of which has been already industrially established. Therefore, γ-PGA is highly attractive, promising food ingredient in the food industry. Several food applications using its physiological and physical properties modifying and taste perception modifying function have been demonstrated at present. However, the mechanism which γ-PGA demonstrates its functions and the relationships between the functions and its structural properties (molecular weight, d/l ratio, etc.) has not been understood. Detailed research in this area will be needed and clarity in this area will lead to develop more attractive applications of γ-PGA.

Isoflavones as Putative Anti‐aging Food Factors in Asia and Effects of Isoflavone Aglycone‐rich Fermented Soybeans on Bone and Glucose Metabolisms in Post‐menopausal Women

Objective:  Since soy isoflavone intake, high in Japanese and Asian populations was epidemiologically associated with lower risks of cardiovascular diseases(CVD), we focused on soy isoflavone effects on other risks of lifestyle‐related diseases and investigated whether or not the intake of isoflavone aglycone‐rich fermented soybeans affected bone and glucose metabolisms in post‐menopausal women.