TABLE 1.

The interaction of flavonoids and gut microbiota.

Class	Compounds	Dietary source	Gut microbiota/Enterobacterial metabolic enzyme	End-products	End-products biological function	Ref.
Flavonol	Quercetin	Onions, kale, broccoli, beans, black currants, apples, tea	Clostridium orbiscindens, Eubacterium oxidoreducens, Butyrivibrio spp.	Phenylacetic acid, 4-HPPA, protocatechuic acid, (3,4-dihydroxy phenyl) propionic acid, and 4-hydroxybenzoic acid	Antitumour, and anti-inflammatory	Winter et al. (1989), Hollman and Arts. (2000); Bowey et al. (2003), Braune and Blaut. (2011), Luo et al. (2014)
	Kaempferol	Fruits, vegetables, and tea	Clostridium strains	Phenylacetic acid	Antioxidation	Simpson et al. (1960), Winter et al. (1989), Guo et al. (2014), Villarreal et al. (2019)
	Icariin		Streptococcusmrg-ICA-benterococcusmrg-ICA-E, and Blautia MRG-PMF-1	Icariside II, icartin, and desmethylicaritin	Antitumour, and immunoregulation	Wu et al. (2016a); He et al. (2020)
Flavanones	Hesperidin	Citrus fruits	Human fecal flora	Hesperetin	Anti-inflammatory, antioxidation, antibacterial, and anticancer cardiovascular	Kim et al. (1998), Tomás-Barberán and Clifford. (2000)
	Naringenin	Citrus fruits	Clostridium strains	3-(4-hydroxyphenyl) propionic acid, phlorogucinol	Free radical scavenging, anti-hyperlipidemic	Winter et al. (1989), Tomás-Barberán and Clifford. (2000)
Flavones	Luteolin	Sweet red pepper, cellery, cauliflower	Rat fecal flora	3-(2,4-dihydroxyphenyl)- propionic acid	Antitumour, anti-inflammatory, and antioxidation	Hollman and Arts. (2000), Aura. (2008), Wang et al. (2013)
	Baicalin		β-D-glucuronidase	Baicalein	Free radical scavenging, anti-tumour, and anti-HIV	Chang et al. (2008), Assini et al. (2013)
	Apiin	Sweet red pepper, cellery, cauliflower	Bacteroides distasonis and Eubacterium ramulus	Apigenin, naringenin, and p-hydroxyphenyl propionic acid	Antidepressant	Hollman and Arts. (2000); Liu and Zhao. (2004); Serra et al. (2012)
Isoflavonoids	Daidzein	Soy products	Bacteroide ovatus spp., Streptococcus intermedius spp., Ruminococcus productus, SNU-Julong 732 (AY310748), Enterococcus faecium EPI1, Lactobacillus mucosae EPI2, Finegoldia magna EPI3, and Veillonella spp. EP	Equol	Anti-diabetic and myocarditis	Hur et al. (2002), Lilian et al. (2002), Hanske et al. (2009), Cassidy et al. (2010), Yin et al. (2016)
	Genistein	Soy products	-	Dihydrogenistein, 6′-Hydroxy-O-demethylangolensin	Anti-bacteria	Cassidy et al. (2010)
Flavan-3-ol	Catechin and Epicatechin	Tea, red wine, chocolate	Clostridium cocoides-Eubacterium rectale group	3-(3-hydroxyphenyl) propionic acid, 5- (30,40-dihydroxyphenyl)-γ-valerolactone, 5-(30-hydroxyphenyl)-γ-valerolactone, 3-hydroxyhippuric acid pyrogallol, 5-(3,4-dihydroxyphenyl) valeric acid	Anti-oxidation, anti-bacteria and protect the heart and brain organs	Hollman and Arts. (2000), Tzounis et al. (2008)