Despite the "chloro" of the name, chlorogenic acids contain no chlorine. Instead, the name comes from the Greek χλωρός (khloros, light green) and -γένος (genos, a suffix meaning "giving rise to"), pertaining to the green color produced when chlorogenic acids are oxidized.
Structural properties
Structurally, chlorogenic acid is the ester formed between caffeic acid and the 3-hydroxyl of L-quinic acid.[3][4] Isomers of chlorogenic acid include the caffeoyl ester at other hydroxyl sites on the quinic acid ring: 4-O-caffeoylquinic acid (cryptochlorogenic acid or 4-CQA) and 5-O-caffeoylquinic acid (neochlorogenic acid or 5-CQA). The epimer at position 1 has not yet been reported.[2]
Structures having more than one caffeic acid group are called isochlorogenic acids, and can be found in coffee.[5] There are several isomers, such as 3,4-dicaffeoylquinic acid and 3,5-dicaffeoylquinic acid.[6] and cynarine (1,5-dicaffeoylquinic acid)
Biosynthesis and natural occurrence
The biosynthetic precursor to chlorogenic acid is 4-coumaroyl-CoA, containing a single hydroxyl group on the aryl ring, which in turn is produced from cinnamic acid. The hydroxylation of the coumaryl ester, i.e. installing the second hydroxy group, is catalyzed by a cytochrome P450 enzyme.[7]
Chlorogenic acid is under preliminary research for its possible biological effects.[17][18][19]
Chlorogenic acid has not been approved as a prescription drug or food additive recognized as a safe ingredient for foods or beverages.[20] There is not enough evidence to determine whether it is safe or effective for human health, and its use in high doses, such as excessive consumption of green coffee, may have adverse effects.[21]
Nomenclature
The atom-numbering of chlorogenic acid can be ambiguous.[22] The order of numbering of atoms on the quinic acid ring was reversed in 1976 following IUPAC guidelines, with the consequence that 3-CQA became 5-CQA, and 5-CQA became 3-CQA. This article uses the original numbering, which was exclusive prior to 1976, (chlorogenic acid being 3-CQA, while neochlorogenic acid is 5-CQA). Thereafter researchers and manufacturers have been divided, with both numbering systems in use. Even the 1976 IUPAC recommendations are not entirely satisfactory when applied to some of the less common chlorogenic acids.[23]
^Barnes, H. M.; Feldman, J. R.; White, W. V. (1950). "Isochlorogenic Acid. Isolation from Coffee and Structure Studies". J. Am. Chem. Soc. 72 (9): 4178–4182. doi:10.1021/ja01165a095.
^Clifford, M. N. (2003). "14. The analysis and characterization of chlorogenic acids and other cinnamates". In Santos-Buelga, C.; Williamson, G. (eds.). Methods in Polyphenol Analysis. Cambridge: Royal Society of Chemistry. pp. 314–337. ISBN978-0-85404-580-8.
^Macheiner, Lukas; Schmidt, Anatol; Schreiner, Matthias; Mayer, Helmut K. (2019). "Green coffee infusion as a source of caffeine and chlorogenic acid". Journal of Food Composition and Analysis. 84: 103307. doi:10.1016/j.jfca.2019.103307. S2CID202882087.
^Tajik, N; Tajik, M; Mack, I; Enck, P (2017). "The potential effects of chlorogenic acid, the main phenolic components in coffee, on health: A comprehensive review of the literature". European Journal of Nutrition. 56 (7): 2215–2244. doi:10.1007/s00394-017-1379-1. PMID28391515. S2CID5177390.
^Onakpoya, I. J.; Spencer, E. A.; Thompson, M. J.; Heneghan, C. J. (19 June 2014). "The effect of chlorogenic acid on blood pressure: a systematic review and meta-analysis of randomized clinical trials". Journal of Human Hypertension. 29 (2): 77–81. doi:10.1038/jhh.2014.46. PMID24943289. S2CID2881228.