Polyacid Digestion

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);

Polyacids	Common	Species examples	All consumers	Prevalence in food	Human digestion, metabolism, interactions	Structure
Aconitate	14	Acidaminococcus fermentans; Citrobacter freundii; Citrobacter koseri; Cronobacter sakazakii; Enterobacter asburiae; Enterobacter cancerogenus; Enterobacter cloacae;	90	Isolated from cane-sugar molasses, chicory root,malt barley, passion fruit, sugar beet, rice and tomatoes; cis: cow's milk, shallots, yams and sweet potatoes	Generated from citrate through aconitate hydratase as part of the TCA cycle. Both cis- & trans-isomer serum concentrations increase in patients with chronic kidney disease (Toyohara2010).
Adipate	0		59	From beetroot and sugar cane.	Can be conjugated with CoA to form adipyl-CoA, which can enter the adipate catabolic pathway. This substrate is catabolised to succinyl-CoA and Ac-CoA, both of which enter the TCA cycle. Serum concentrations increase in patients with chronic kidney disease (Toyohara2010).
Azelate	0		31	Found in wheat, rye and barley. Also from fermented foods, such as olives.	Involved in the beta-oxidation pathway since metabolites of azelate, such as pimelic acid, are found in the serum and urine (Passi1989). Serum concentrations increase in patients with chronic kidney disease (Toyohara2010).
Citraconate	0		9	Produced upon dry distillation of citric acid.	Serum concentrations increase in patients with chronic kidney disease (Toyohara2010). Also elevated in patients with methylmalonic acidemia.
Citrate	30	Bacillus cereus; Bacillus licheniformis; Bacillus subtilis; Bacteroides bouchesdurhonensis; Bacteroides ndongoniae; Citrobacter farmeri; Citrobacter freundii;	302	Lemon, lime, oranges and grapefruit.	Readily absorbed and shunted into the TCA cycle. Serum concentrations increase in patients with chronic kidney disease (Toyohara2010).
Fumarate	21	Campylobacter concisus; Campylobacter gracilis; Campylobacter ureolyticus; Citrobacter farmeri; Citrobacter freundii; Citrobacter koseri; Cronobacter sakazakii;	243	Food additive and flavour enhancer in tortillas, sourdough, rye bread and fruit juices.	An intermediate in the TCA cycle.
2-ketoglutarate	2	Klebsiella pneumoniae; Stenotrophomonas maltophilia;	66	From meat, fish, and dairy products.	An intermediate in the TCA cycle. Endogenously produced during catabolism of glutamate. Serum concentrations decline in patients with chronic kidney disease (Toyohara2010).
Glutarate	1	Enterobacter hormaechei subsp. hormaechei;	55	Produced endogenously.	Produced as a metabolite of lysine and tryptophan metabolism. Serum concentrations increase in patients with chronic kidney disease (Toyohara2010).
Itaconate	1	Enterobacter hormaechei subsp. hormaechei;	31	A product of dry citrate distillation. Sources include crusts of sourdough and rye bread.	An intermediate in the TCA cycle.
Malate	9	Bacteroides bouchesdurhonensis; Citrobacter farmeri; Desulfitobacterium hafniense; Desulfovibrio desulfuricans; Enterococcus faecalis; Hafnia alvei; Paraclostridium bifermentans;	186	Contributes to the sour taste of fruits. Found in apples, apricots, blackberries, blueberries, cherries, grapes, peaches, pears and plums. Used as a food additive.	An intermediate in the TCA cycle (L-malate).
D-Malate	5	Citrobacter freundii; Citrobacter koseri; Klebsiella pneumoniae; Klebsiella quasipneumoniae subsp. quasipneumoniae; Raoultella ornithinolytica;	56	Food additive as a DL-mixture of isomers.	It is unclear (to the author) what the fate of the D-isomer is in humans. A WHO report (WHO1967) stated 'parenterally administered DL-malic acid in rabbits and dogs only D(-)-malic acid was recovered in the urine', which suggests D-malate is excreted in humans, also.
L-Malate	13	Anaerotruncus colihominis; Citrobacter farmeri; Citrobacter freundii; Citrobacter koseri; Cronobacter sakazakii; Enterobacter asburiae; Enterobacter cancerogenus;	174	See 'Malate'	See 'Malate'
Maleate	0		4	Can be ingested if food is contaminated.	Low levels, or occasional ingestion, is probably not harmful; however, significant consumption may lead to kidney damage in humans (Fu2013), and is known to be highly toxic to dogs (Schweighauser2015).
Malonate	6	Citrobacter koseri; Klebsiella aerogenes; Klebsiella oxytoca; Klebsiella pneumoniae; Klebsiella quasipneumoniae subsp. quasipneumoniae; Raoultella ornithinolytica;	99	Found in beetroot, corn, scarlet beans, common beets, and cow's milk.	Denovo lipogenesis begins when fatty acid synthase catalyses the condensation of malonyl-CoA and acetyl-CoA to acetoacetyl-CoA. Serum concentrations increase in patients with chronic kidney disease (Toyohara2010).
Mesaconate	0		14	Prepared from citric acid.
Mucate	12	Citrobacter farmeri; Citrobacter freundii; Citrobacter koseri; Enterobacter asburiae; Enterobacter cancerogenus; Enterobacter cloacae; Klebsiella aerogenes;	75	Mucic acid (galactric acid) is used as a food additive; found broadly in fruits, vegetables and cow's milk.
Oxalate	1	Oxalobacter formigenes;	6	Found in many plants, including pepper, parsley, spinach, rhubarb, fruits, cocoa, nuts, and seeds.	Calcium salts of oxalate are poorly absorbed, but mixed iron salts likely enter the bloodstream (Robertson2011). High concentrations of oxalic acid is associated with primary hyperoxaluria, diabetes, and the formation of kidney stones. Oxalate may be generated in vivo from the breakdown of uracil and orotic acid.
Pimelate	0		18		Probably derived from malonyl-CoA. Excreted in elevated amounts in the urine of individuals with mitochondrial beta-oxidation disorders. Serum concentrations increase in patients with chronic kidney disease (Toyohara2010).
Saccharate	11	Citrobacter farmeri; Citrobacter freundii; Citrobacter koseri; Enterobacter asburiae; Enterobacter cancerogenus; Enterobacter cloacae; Enterobacter hormaechei subsp. hormaechei;	55		Chelates metals, including calcium.
Sebacate	0		29	From castor oil.	Serum concentrations increase in patients with chronic kidney disease (Toyohara2010).
Suberate	0		28		Suberate is a byproduct of long-chain fatty acid metabolism outside the mitochondria. Present in urine of people with fatty acid oxidation disorders, such as a lack of carnitine or riboflavin.
Succinate	19	Citrobacter farmeri; Citrobacter freundii; Citrobacter koseri; Cronobacter sakazakii; Desulfitobacterium hafniense; Dialister invisus; Dialister succinatiphilus;	266	Found in broccoli, rhubarb, beetroot, fresh meat extracts, various cheeses, and sauerkraut.	An intermediate in the TCA cycle. Serum concentrations increase in patients with chronic kidney disease (Toyohara2010).
Methyl-Succinate	1	Kosakonia cowanii;	30
meso-Tartrate	3	Citrobacter freundii; Megasphaera elsdenii; Raoultella ornithinolytica;	29	Extracted during wine-making processes.
D-Tartrate	2	Providencia alcalifaciens; Providencia rettgeri;	24	Extracted during wine-making processes, or by semisynthetic and microbial processes.
L-Tartrate	3	Citrobacter freundii; Citrobacter koseri; Providencia rettgeri;	33	Naturally occurring tartrate (L-form) is found in wine, grapes, bananas and citrus fruits. Together with bicarbonate, it is used as a raising agent in cooking.	Elevated levels are potentially toxic to muscles because tartrate inhibits the production of malic acid. Only ~12% of ingested tartrate is excreted in the urine, but 66% of injected material was recovered through this route. This suggests tartrate is poorly absorbed and little - if any - tartrate is metabolised (Younes2020).
Tricarballylate	4	Citrobacter farmeri; Citrobacter freundii; Enterobacter hormaechei subsp. hormaechei; Klebsiella quasipneumoniae subsp. quasipneumoniae;	17		Binds to magnesium strongly, and may lead to a metal deficiency. Also inhibits aconitase.