Table 1.

Representative Flavonoids and their Underlying Metabolism by Gut microbiota.

Flavonoid Subclass	Name of Flavonoid	Structure of Flavonoid	Dietary Source	Metabolites Produced by Gut Microbiota	Bacteria Involved in Metabolism	Enzymes Involved in Metabolism	Site of Metabolism	Conversion Mechanism		Effect of Microbiota on Flavonoids	Model Used		References
											In Vivo	In Vitro
Flavonol	1. Rutin		Lemons, berried, limes and oranges	Quercetin -3- O- glucoside Quercetin	Lachnoclostridium Eisenbergiella Escherichia Parabacteroides Erysipelatoclostridium	α-rhamnosidases β-glucosidases	Colon	Hydrolysis of rutin to remove sugar moiety		Permit the absorption of the aglycone Enhance bioavailability		10 fecal samples from healthy individual following omnivore diet.	[29,30,31,32,33]
	2. Fisetin		Persimmon and onions	No available data									[34,35]
	3.Kaempferol		Tea, berries and cruciferous vegetables	Kaempferol -3-O- glucoside p-coumaric acid kaempferol 3-(4 hydroxyphenyl) propionic acid 3-phenylpropionic acid	Lactobacillus paracasei A221	β-glucosidases	Intestinal tract	(A)Degradation through multiple chemical reactions: - Deglycosylation - Reduction - Dehydroxylation (B) Hydrolysis		Permit the absorption of the aglycone Enhance bioavailability	Mice	3 fecal samples from healthy individual Caco-2 intestinal barrier model	[36,37,38,39]
	4. Quercetin		Black currants, cherries, apples and chokeberries	4-hydroxybenzoic acid 3,4-dihydroxyphenylacetic acid 3,4-dihydroxybenzoic 3-(3-hydroxyphenyl) propionic acid	Bacteroides fragilis Clostridium perfringens Eubacterium ramulus Streptococcus S-2 Lactobacillus L-2 Bifidobacterium B-9 Bacteroides JY-6	Lactate phlorizin hydrolase	Small intestine	Deglycosylation		Enhance bioavailability	Mice	87 fecal samples from healthy elderly individual	[40,41,42,43,44,45]
	5. Isorhamnetin		Ginkgo biloba and Hippophae rhamnoides	3-O-neohesperidoside Isorhamnetin -3- glucoside Aglycone isorhamnetin	Escherichia Enterococcus Bacillus.	Not identified	Small intestine	Deglycosylation		Permit the absorption of the aglycone	Rats	1 fecal sample from healthy female	[46,47]
	6. Morin		Psidium guajava, Prunus dulcis (Almond), chlorophora tinctoria and fruits	Morin glucuronides Morin sulfates	No available data								[12]
Flavanones	7. Hesperidin		Orange citrus aurantium	Hesperetin	Not identified	Rutinose	Large intestine	Cleaves the attached rutinose moiety	Permit the absorption of the aglycone Enhance bioavailability			fecal/ blood samples from 18 Lewis male rats	[48,49,50,51]
	8. Naringenin		C.aurantium (chinese herbs) and grapefruit	Aglycone naringenin	Ruminococcus gauvreauii Bifidobacterium catenulatum Enterococcus caccae Eubacterium ramulus	Chalcone isomerase	Large intestine	Remove sugar group	Permit the absorption of the aglycone Enhance bioavailability			fecal samples from healthy individuals	[52,53,54]
	9. Eriodictyol		Lemon (Eriocitrin), Torr, Eridictyon californicum,	Eriodictyol 3,4-dihydroxyhydrocinnamic acid Phloroglucinol	Parabacteroides distasonis Bacteroides uniformis JCM 5828	Chalcone isomerase	Colon	O-Deglycosylation	Permit the absorption of the aglycone Enhance bioavailability			fecal samples from healthy individuals	[55,56,57]
Isoflavones	10. Genistein		Fava and soy beans	Dihydrogenistein 6-hydroxy-O-desmethylangolensin 2-(4-hydroxyphenyl) propionic acid	Lactobacillus Eubacterium ramulus	Lactate phlorizin hydrolase	Small intestine	Fermentation by anerobic bacteria	Permit the absorption of the aglycone Enhance bioavailability			Samples from C57BL/6 female mouse	[58,59,60,61]
	11. Daidzein		Soybeans, nuts and soymilk	Dihydrodaidzein O-desmethylangolensin S- equol	Clostridium-like strain	β- glucosidase Lactate phlorizin hydrolase	Colon	Reduction	Permit the absorption of the aglycone Enhance bioavailability		Mice		[62,63,64]
Anthocyanins	12. Cyanidin		Bilberry, blueberry, grapes, blackberries, hawthorn	Cyanidin-3- glucoside	Clostridium saccharogumia Eubacterium ramulus	Combined activity of bacteria and host enzymes	Small intestine	Degrade polyphenolic glycosides	Permit the absorption of the aglycone Enhance bioavailability		Dawley rats	Fecal samples from healthy individuals	[65,66,67]
	13. Delphinidin		Dark grapes, eggplant, berries, red cabbage,	Gallic acids	Lactobacillus	β-d-glucuronidase β-d-glucosidase α-rhamnosidase α-galactosidase	Colon	Cleavage of glycosidic bonds	Permit the absorption of the aglycone Enhance bioavailability		Mice		[68,69,70,71,72]
	14. Pelargonidin		Bilberry and ficus bengalensis Linn	4-hydroxybenzoic	Lactobacillus	β-d-glucosidase β-d-glucuronidase α-galactosidase α-rhamnosidase	Colon	Cleavage of glycosidic bonds	Permit the absorption of the aglycone Enhance bioavailability		Mice		[73,74]
Flavones	15. Baicalein		Scutellaria lateriflora L	Baicalein	E. coli	β-glucuronidase	Intestine	Hydrolysis to remove moiety	Permit the absorption of the aglycone Enhance bioavailability		Mice	HCT-166 cells SW-480 cells	[75,76,77,78]
	16. Luteolin		broccoli, celery and parsley,	No available data									[12]
	17. Diosmin		Citrus fruits	Diosmetin	Not identified	α- glucosidase β- glucosidase	Small intestine	Hydrolysis	Enhance bioavailability			Blood samples from healthy participants	[79,80,81,82]
	18. Apigenin		Tea, chamomile, parsley and oranges	3-(4-hydroxyphenyl) propionic acid Apigenin	Bacteroides distasonis Eubacterium ramulus Clostridium orbiscindens	β- glucosidase lactase-phlorizin hydrolase	Small intestine	Glucuronidation Hydrolysis	Enhance bioavailability		Rats	Fecal and urine samples	[83,84,85,86]
	19. Tangeretin		Poncirus trifoliate L, citrus fruit	Tangeretin-O-glucuronides	Lactobacillus Bifidobacterium	Possibly by: A) rhamno glucosides B) C- glycosyl	Small intestine	Demethylation	Permit the absorption of the aglycone		Rats		[87,88]
	20. Wogonin		Scutellaria baicalensis Georgi	Wogonin	Not identified	β-glucuronidase	Intestine	Hydrolysis	Enhance absorption and bioavailability		Sprague-Dawley rats		[89,90,91,92]
	21. Chrysin		Honey	Chrysin glucuronides	Flavonifractor plautii ATCC 49531	Flavone reductase	Intestine	Reduction	catalyzes the hydrogenation of the C2–C3 double bond			ATCC 49,531 strain	[93,94,95]