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Erratum

	INTRODUCTION

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Zhang, Y., Wang, G.-J., Song, T. T., Murphy, P. A. and Hendrich, S. (1999) Differences in disposition of the soybean isoflavones, glycitein, daidzein and genistein in humans with moderate fecal isoflavone degradation activity. J. Nutr. 129: 957–962.

The isoflavone content of soy milk and soy germ used in this study was calculated according to isoflavone extinction coefficients and normalized to the total daidzein, genistein and glycitein calculated as aglycone isoflavones. Due to re-purification and recent commercial availability, the extinction coefficients of acetylgenistein and acetyldaidzein were re-evaluated. The new extinction coefficients for these two compounds were different from those previously used (Acetyldaidzin: old = 16331 [Ohta et al. 1979 ]; new = 29007. Acetylgenistin: old = 18197 [Ohta et al. 1980 ]; new = 38946). The new molar extinction coefficients were evaluated after isolating acetyldaidzin and acetylgenistin from soybeans (Wang and Murphy 1994 ). These extinction coefficients were compared with and agreed closely with extinction coefficients derived from acetyl standards generously donated by LC Laboratories, [Woburn, MA]. Minimal differences were found between the acetylglycitin extinction coefficients determined in our laboratory and the published values (Kudou et al. 1991 ). According to these new data, the isoflavone contents of the soygerm and soymilk used in this feeding study were overestimated in the original paper. The recalculated isoflavone contents in both soy milk and soygerm powders are shown in Table 1 . Urinary isoflavone excretion as a percentage of ingested dose was recalculated accordingly. Because there was no difference in urinary excretion as percentage of ingested dose according to the soy food administered, as reported previously, combined data are shown in Table 2 . Total urinary excretion of daidzein (52.4%) was slightly greater than that of glycitein (46.7%), but there was no significant difference between them (p = 0.08). Both daidzein and glycitein excretion were significantly greater than that of genistein (37.0%) (p = 0.004 and p = 0.01 respectively). Female subjects excreted slightly greater amounts of all three compounds at each time point than did male subjects (p = 0.03). The overall urinary excretion as percentage of ingested dose (total over 48 h) of daidzein, genistein and glycitein were 57.4, 42.3 and 50.2% in females, and 48.8, 36.4, and 42.1% in males, respectively. Based on these new data, the urinary disposition of the three main isoflavones showed that more daidzein and glycitein were excreted than was genistein, and daidzein and glycitein excretions were similar. This disposition pattern was different from that reported originally (glycitein greater than daidzein, Zhang et al. 1999 ). On reverse phase HPLC analysis, daidzein and glycitein appeared earlier than genistein (by more than 5 min), and glycitein was eluted about 1 min later than was daidzein. These HPLC results showed that daidzein and glycitein had similar hydrophobicity and that they were more hydrophilic than was genistein. The absence of the 5-OH group makes both daidzein and glycitein more hydrophilic than genistein. The 5-OH forms part of an internal hydrogen bond that makes genistein more hydrophobic although it contains more free hydroxyls than glycitein or daidzein. The absence of the 5-OH probably makes daidzein and glycitein less susceptible to microbial breakdown than is genistein (Griffiths and Smith, 1972 ). The newly calculated urinary disposition of the isoflavones may be explained by their structural properties, genistein being less bioavailable as reflected in urinary excretion because of its greater susceptibility to microbial breakdown than either daidzein or glycitein. Compared with daidzein, genistein has been shown to be more susceptible to breakdown by gut microorganisms during anaerobic incubations of human fecal samples (Xu et al. 1995 ). But glycitein metabolism by gut microflora is not yet known. Isoflavone bioavailability has only been compared between genders in one other study. Lampe et al. (1998) fed people with soy protein containing 22 mg daidzein and 8 mg genistein for 4 days. They did not find any differences in daily excretion of daidzein, genistein and O-desmethylangolensin between equol excreters and nonexcreters and between men and women. The slight gender differences in isoflavone urinary excretion observed in this study are not readily explained and need further study. Overall, our recalculation showed that daidzein and glycitein had similar bioavailability and they were more bioavailable than was genistein, based on urinary disposition.

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3. Lampe J. W., Karr S. C., Hutchins A. M., Slavin J. L. Urinary equol excretion with a soy challenge: influence of habitual diet. Proc. Soc. Exp. Biol. Med. 1998;217:335-339[Abstract]

4. Ohta N., Kuwata G., Akahori H., Watanabe T. Isoflavonoid constituents of soybeans and isolations of a new acetyl daidzein. Agric. Biol. Chem. 1979;43:1415

5. Ohta N., Kuwata G., Akohori H., Watanabe T. Isolations of a new isoflavone acetyl glucoside, 6''-O-acetyl genistin. Agric. Biol. Chem. 1980;44:469

6. Wang H.-J., Murphy P. A. Isoflavones of commercial soybean foods. J. Agric. Food Chem. 1994;42:1666-1673

7. Xu X., Harris K. S., Wang H.-J., Murphy P. A., Hendrich S. Bioavailability of soybean isoflavones depends upon gut microflora in women. J. Nutr. 1995;125:2307-2315

8. Zhang Y., Wang G.-J., Song T. T., Murphy P. A., Hendrich S. Differences in disposition of the soybean isoflavones, glycitein, daidzein and genistein in humans with moderate fecal isoflavone degradation activity. J. Nutr. 1999;129:957-962[Abstract/Free Full Text]

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