CHARACTERIZATION OF URINARY ISOFLAVONE METABOLITES EXCRETED AFTER THE CONSUMPTION OF SOY FLOUR OR SOYBEAN PASTE USING LC-(ESI)MS/MS

Authors

  • EUNMI KOH,

    1. Department of Food Science and Technology, University of California at Davis, One Shields Avenue, Davis, CA 95616
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  • ALYSON E. MITCHELL

    Corresponding author
    1. Department of Food Science and Technology, University of California at Davis, One Shields Avenue, Davis, CA 95616
      TEL: 530-752-7926; FAX: 530-752-4759; EMAIL: aemitchell@ucdavis.edu
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TEL: 530-752-7926; FAX: 530-752-4759; EMAIL: aemitchell@ucdavis.edu

Abstract

ABSTRACT

Isoflavones are thought to have an important role in the prevention of hormone-related diseases. This study was undertaken to identify the profile of urinary isoflavone metabolites collected within 24 h after the consumption of unfermented or fermented soy foods. The proportions of β-glycosides and aglycones to total isoflavone intake were much higher in soybean paste than soy flour. Twenty urinary isoflavone metabolites were identified using LC(ESI)-MS/MS. After enzymatic hydrolysis, glucuronide forms of daidzein and genistein accounted for 76 and 86% of total isoflavones, demonstrating that the majority of urinary isoflavone metabolites are glucuronide conjugates. When comparing the areas under curves of two foods, total urinary isoflavones excretion was higher in subjects consuming soybean paste than in subjects consuming soy flour. Genistein glucuronides are cleared more slowly than daidzein glucuronides after soy consumption. These findings indicate that the bioavailability of isoflavones may be influenced depending on the chemical composition of soy isoflavones.

PRACTICAL APPLICATIONS

Sensitive LC(ESI)-MS/MS methods characterizing the broad range of flavonoid metabolites formed in response to a “realistic” dietary exposure are critical for understanding what metabolites are circulating in plasma and have biological activity. Once identified these metabolites can be used to probe mechanisms of biological action, explore synergy between metabolites and better define their role in human health.

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