Coffee beans are a well-known source of chlorogenic acids (CGAs), a large class of esters formed between (-)-quinic acid and trans-hydroxycinnamic acids (caffeic, ferulic but also p-coumaric and sinapic acids). These compounds are important for their influence on the beverage sensorial properties, being aroma precursors of key volatile compounds, for product authenticity and traceability and for their biological activity with potential benefits on human health. This class of compounds counts several positional isomers which cannot be easily distinguished without adequate standards and reliable methods of analysis. Recently, thanks to studies of MS fragmentation pattern, identification of many isomers has been achieved by proper LC-MS protocols and many structures of new CGA isomers have been disclosed. From a quantitative point of view, CQAs monoester isomers are by far the most abundant, reaching together more than 80% of total chlorogenic acids. In these compounds the hydroxyl groups at C-3, C-4 and C-5 of the (-)-quinic acid ring are esterified with a single caffeic acid moiety. In addition to CQAs isomers, green coffee beans are particularly rich of two other classes of chlorogenic acid compounds: di-caffeoylquinic acid (diCQAs) and mono-feruloylquinic acid (FQAs) isomers. Much less abundant chlorogenic acids, and for this reason known as “minor”, are mono-p-coumaroylquinic acids (pCoQAs), mono-sinapoylquinic acids (SiQAs), homo di-acylquinic acid isomers such as diferuloylquinic acids (diFQAs) and dimethoxycinnamoylquinic acids (DQAs), and hetero di-acylquinic acid isomers such as caffeoylferuloylquinic acids (CFQAs), caffeoyl-dimethoxycinnamoylquinic acids, feruloyl-dimethoxycinnamoylquinic acids. Minor chlorogenic acids have not been the subject of detailed investigations and their qualitative and quantitative profile are scarcely reported in the literature and mostly focused on the two commercially exploited coffee botanical species: Coffea arabica and c. canephora. The aim of this work is to offer an overview of minor CGAs profile in different green Coffea species. Qualitative and quantitative robust data are the prerequisite to select best sources for isolation and then to have the chance to investigate bioavailability and biological activity of these neglected chlorogenic acids. Finally, minor chlorogenic acids profile may play an important role in disclosing the biosynthetic pathway of chlorogenic acids in coffee which is not yet fully clarified.

Neglected coffee chlorogenic acids: p-coumaroyl-, sinapoyl- and di-acyl-quinic acid isomers in different coffee botanical species

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