Sequencing of red wine proanthocyanidins by UHPLC-ESI-Q-ToF

Phenolic compounds are considered as secondary metabolites and are widespread in the plant kingdom [1, 2]. These compounds are present in vegetables [3], fruits [4], tea [5] and red wine [6-8]. They are known for their oxidative defense [9], their ability to reduce certain cancers [10, 11], their preventive activity against infectious [12] and degenerative diseases [13,14]. Among these phenolic compounds, the proanthocyanidins (PAs) or flavan-3-ols represent a significant family and they play an important role during wine making [15] and red wine tasting [16]. Four monomeric units [17, 18] are present in the grape and red wine: (+)-catechin (C), (-)-epicatechin (EC), (-)-epigallocatechin (EGC) and (-)-epicatechin-3-O-gallate (ECG) (Figure 1). These monomers give rise to the formation of oligomers and polymers via an interflavan bond between C4 of the top unit and C6 or C8 [4, 19] of the lower unit and sometimes an additional ether bond between C2 of the top unit and C5 or C7 of the lower unit [20, 21]. (-)-epicatechin (EC), (+)-catechin (C) and (-)-epicatechin-3-O-gallate (ECG) are mainly located in grape seeds, whereas the monomeric unit (-)-epigallocatechin (EGC) is only present in grape skins [22, 23]. These compounds present in red wine are involved in the astringency phenomenon [16, 17], the bitterness, the body [24], the wine aging [25] and the organoleptic properties [26]. These proanthocyanidins have been studied by analytical method such as high-performance liquid chromatography (HPLC) [27], mass spectrometry coupled with UHPLC system [28], and nuclear magnetic resonance (NMR) [29]. In the current study, we first describe the theoretical possibilities to form oligomers with A and B-type interflavan bond. In a second part, we describe specific fragmentation pathways allowing the sequencing of proanthocyanidins in red wine using a UHPLC-ESI-Q-ToF. JOURNAL OF APPLIED BIOANALYSIS, Apr. 2015, p. 46-54. http://dx.doi.org/10.17145/jab.15.009 (ISSN 2405-710X) Vol. 1, No. 2