Plasma metabolites of dietary flavonoids after combination meal consumption with onion and tofu in humans

Toshiyuki Nakamura, Kaeko Murota, Shun Kumamoto, Kazuhiro Misumi, Noriko Bando, Shinichi Ikushiro, Nobuyuki Takahashi, Keiko Sekido, Yoji Kato, Junji Terao

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)


Scope: The effect of food combination on metabolic profile in postprandial plasma has hardly been reported. We investigated the absorption and metabolism of quercetin and soy isoflavones in humans after combination meal consumption. Methods and results: Five healthy volunteers ingested sautéed onion and tofu, and the plasma metabolites of quercetin and isoflavones were analyzed. Quercetin and genistein were incubated with human intestinal Caco-2 cells and human hepatoma HepG2 cells to further analyze the influence of simultaneous supply to the small intestine and the liver. Glucuronosyl conjugates of quercetin and methylated quercetin were the major plasma metabolites in the case of onion intake. Plasma metabolites with the single serving of tofu were both glucuronide and sulfate metabolites of isoflavones. Interestingly, quercetin sulfate was only detected after the combined intake of sautéed onion and tofu, accompanied with a decrease in sulfated isoflavones. Besides, quercetin was shown as the preferential substance for phase II enzymes over genistein in both Caco-2 and HepG2 cells. Conclusion: These results indicate that, when flavonoids and isoflavonoids were ingested together, the metabolic conversions in the small intestine and/or the liver could be altered, resulting in the variation of the postprandial profiles of the plasma metabolites.

Original languageEnglish
Pages (from-to)310-317
Number of pages8
JournalMolecular Nutrition and Food Research
Issue number2
Publication statusPublished - Feb 2014
Externally publishedYes


  • Bioavailability
  • Combination meal
  • Human metabolites
  • Isoflavone
  • Quercetin

ASJC Scopus subject areas

  • Biotechnology
  • Food Science


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