High Molecular Weight Persimmon (Diospyros kaki L.) Proanthocyanidin: A Highly Galloylated, A-Linked Tannin with an Unusual Flavonol Terminal Unit, Myricetin

Abstract

MALDI-TOF MS suggested that the high molecular weight proanthocyanidin (condensed tannin) from persimmon (Diospyros kaki L.) pulp comprised a heteropolyflavanol series with flavan-3-O-galloylated extenders, flavan-3-ol and flavonol terminal units, and A-type interflavan linkages. Thiolysis-HPLC-ESI-MS with DAD, electrochemical, and ESI-MS detection confirmed a previously unreported terminal unit, the flavonol myricetin, in addition to the typical flavan-3-ols catechin and epigallocatechin gallate. The extender units were epicatechin, epigallocatechin, (epi)gallocatechin-3-O-gallate, and (epi)catechin-3-O-gallate. The crude tannin had a high prodelphinidin content (65%) and a high degree of 3-O-galloylation (72%). The material was fractionated on Toyopearl TSK-HW-50-F to yield fractions distinguished by degree of polymerization (DP). Thiolysis suggested that the persimmon tannin was composed of polymers ranging from 7 to 20 kDa (DP 19-47), but sizes estimated by GPC were 50-70% smaller. The crude material was chemically degraded with acid to yield products that were amenable to NMR and ESI-MS analysis, which were used to establish for the first time that persimmon tannin has a mixture of B-type and A-type linkages.

Characterisation of phenolic acids, flavonoids, proanthocyanidins and antioxidant activity of water extracts from seed coats of marama bean [Tylosema esculentum] – an underutilised food legume

“…Peak 3 was identified as (epi)gallocatechin benzylthioether (MW = 428) and peak 4 was identified as (epi)gallocatechin-3-O-gallate benzylthioether (MW = 580). Similar mass spectra data for these compounds were reported in proanthocyanidins from persimmon fruit (Li et al, 2010). The compound eluting in peak 5 was identified as (epi)catechin benzylthioether (MW = 412).…”

Molecular weight and protein-precipitating ability of condensed tannins from warm-season perennial legumes

“…First, polyphenols may interact with chromatographic stationary phases, such as PL-gel, leading to overestimates in molecular weight (Williams et al 1983). Second, calibration plots generated using commercially available standards such as polystyrene tend to underestimate CT sizes (Li et al 2010). Finally, the relationship between hydrodynamic volume and molecular weight appears to be a complex function of the subunit composition for different polyphenols, so even with CT standards it is difficult to generate a reliable calibration plot (Kennedy & Taylor 2003).…”

“…The apparent weight-average molecular weights of CT purified from these legumes, relative to polystyrene standards, ranged from 552 to 1483 Da (Table 1). The two most widely used methods for establishing the molecular weight of CT are thiolysis followed by quantitative HPLC analysis of the extender and terminal units (Li et al 2010) or GPC (Bae et al 1994). Thiolysis provides accurate estimates of the mean degree of polymerization, but not the molecular weight distribution (Kennedy & Taylor 2003).…”

High molecular weight persimmon tannin is a potent antioxidant both ex vivo and in vivo

“…For polymeric proanthocyanidins, antioxidant activities are probably a consequence of structural features such as the monomeric flavan-3-ol units, the types of interflavan bonds, and the degree of polymerization. Our previous work (Li, Leverence, et al, 2010) showed that HMWPT has a unique structure compared to other plant proanthocyanidins: It comprises an …”

“…The HMWPT was characterized by MALDI-TOF, thiolysis-HPLC-ESI-MS and NMR (Li, Leverence, et al, 2010). The mean degree of polymerization of HMWPT was estimated to be 26 by thiolysis.…”