Aromatic Acids

KEY Fermenters: Oxidation or fermentation by gut bacteria producing acid; Use: Utilisation or assimilation by gut bacteria; Common: Combined use and O/F for widespread, moderate and minor gut colonisers (total bacteria: 500);

Aromatic acids	Common	Species examples	All consumers	Prevalence in food	Human digestion, metabolism, interactions	Structure
Benzoate	5	Citrobacter farmeri; Desulfovibrio desulfuricans; Enterobacter hormaechei subsp. hormaechei; Klebsiella pneumoniae; Klebsiella quasipneumoniae subsp. quasipneumoniae;	48	Benzoic acid, often as the sodium salt, is added to soft drinks, fruit juices, fermented vegetables, and high-sugared foods as a preservative. Small quantities are detected in berries, kiwi fruit, oranges, thyme, cabbages, potatoes, nuts and dairy products.	ADI recommendation is generally <0.4 g/day. Benzoic acid is converted to hippurate, and then excreted.
4-Hydroxybenzoate	6	Citrobacter farmeri; Enterobacter hormaechei subsp. hormaechei; Klebsiella oxytoca; Klebsiella pneumoniae; Klebsiella quasipneumoniae subsp. quasipneumoniae; Raoultella ornithinolytica;	86	Significant levels in huckleberries, corianders, onions and in lower concentrations in soybeans, rye bread, coconut, wine, vanilla and almonds.	Formed when chorismate lyase acts on chorismate to 4-HBA and pyruvate. Involved in ubiquinone biosynthesis. Believed to possess oestrogenic activity. In humans administration of 4-HBA restores endogenous CoQ10-biosynthesis in COQ2-deficient cell lines (Herebian2017).
3-Hydroxybenzoate	6	Citrobacter farmeri; Citrobacter freundii; Citrobacter koseri; Enterobacter hormaechei subsp. hormaechei; Escherichia albertii; Klebsiella oxytoca;	34	Found in avocado, cranberries, corn, bilberry, citrus, and beer.	3-HBA is an agonist for both HCA1 (EC50 of 186 μM) and HCA2 (EC50 of 158 μM), inhibiting lipolysis in adipocytes, which may attenuate the effects of dyslipidemia (Juurlink2014).
L-Mandelate	0		4	Found in bitter almonds, apples and wild cherries.	Has been used in the treatment of urinary tract infections in the past, as ingested ammonium mandelate is excreted essentially unchanged (Lyon1935).
Phenol	0		6	Derived as a metabolite of microbiome-degraded phenylalanine (Zaidan2022).	Absorbed into the bloodstream and conjugated in the liver to form p-cresol sulfate (Zaidan2022).
Phenylacetate	7	Enterobacter asburiae; Enterobacter cancerogenus; Enterobacter cloacae; Enterobacter hormaechei subsp. hormaechei; Klebsiella oxytoca; Klebsiella quasipneumoniae subsp. quasipneumoniae; Serratia marcescens;	81	Found in grapes, raspberry, strawberry, several cheeses, wine and black tea.	Can be derived from the breakdown of Phe, via phenylpyruvate. Also formed when 2-phenylethylamine is catabolised in the presence of monoamine oxidase.
p-Hydroxyphenylacetate	0		12	From olives, cranberries, and grapes, as well as corn, beer, oats, wheat, cocoa, and cow's milk.	A metabolite of Tyr breakdown. Individuals on a Mediterranean diet tend to excrete more 4-hydroxyphenylacetate in their urine. Clostridioides difficile decarboxylates this acid to form p-cresol.
m-Coumarate	6	Citrobacter freundii; Enterobacter hormaechei subsp. hormaechei; Klebsiella pneumoniae; Klebsiella quasipneumoniae subsp. quasipneumoniae; Raoultella ornithinolytica; Terrisporobacter glycolicus;	16	Found in olives, corn, beer, carrots, strawberries, grape wines, vinegar and tomatoes. Can also be produced by gut bacteria.	Detected in urine after consumption of coffee and other polyphenol-rich beverages (Ito2005).