Abstract
| - The tanoak (Lithocarpus densiflorus) acorn was a staple food in the Native American diet and is stillused in traditional dishes. Acorns from the genus Quercus have been shown to contain a large rangeof hydrolyzable tannins. However, neither hydrolyzable nor condensed tannins have been characterized in tanoak acorns. The aim of this study was to identify the full range of hydrolyzable andcondensed tannins in extracts of tanoak acorns using liquid chromatography/electrospray ionization−mass spectrometry/mass spectrometry. Condensed tannins were identified as B type oligomers of(epi)-catechin (procyanidins) with a degree of polymerization up to six. Oligomers up to and includingtetramers were identified by UV spectra and MS detection whereas pentamers and hexamers weredetected only by MS. The total concentration of condensed tannins was 464 mg/100 g acorn pericarp.The concentration of propocyanidin monomers, dimers, trimers, and tetramers in acorn pericarp (mg/100 g acorn pericarp) were 95 ± 10.9, 148 ± 35.0, 90 ± 17.9, and 131 ± 1.9, respectively. Noprocyanidins were found in the acorn cotyledon tissue. A total of 22 hydrolyzable tannins were identifiedin methanolic extracts of acorn cotyledon tissue. Gallic acid derivatives predominated and includedgalloylated esters of glucose, hexahydrodiphenoyl esters of glucose, and methylated gallates.Galloylated esters of glucose were present as isomers of galloyl glucose, digalloyl glucose, andtrigalloyl glucose. Mass spectral fragmentation patterns indicate the presence of one gallic acid-galloyl glucose isomer and two gallic acid-digalloyl-glucose isomers. No isomers of tetragalloyl glucoseand pentagalloyl glucose were identified. Ellagic acid and ellagic acid pentoside were also identified. Keywords: Acorn; hydrolyzable tannin; condensed tannin; phenolic; antioxidant; procyanidins;Lithocarpus densiflorus
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