title: Analysis of commercial proanthocyanidins. Part 4: solid state (13)C NMR as a tool for in situ analysis of proanthocyanidin tannins, in heartwood and bark of quebracho and acacia, and related species.
abstract: (13)C NMR is an effective method of characterizing proanthocyanidin (PAC) tannins in quebracho (Schinopsis lorentzii) heartwood and black wattle (Acacia mearnsii) bark, before and after commercial extraction. The B-rings of the constituent flavan-3-ols, catechols (quebracho) or pyrogallols (wattle), are recognized in unprocessed source materials by "marker" signals at ca. 118 or 105ppm, respectively. NMR allows the minimum extraction efficiency to be calculated; ca. 30%, and ca. 80%, for quebracho heartwood and black wattle bark, respectively. NMR can also identify PAC tannin (predominantly robinetinidin), and compare tannin content, in bark from other acacia species; tannin content decreases in the order A. mearnsii, Acacia pycnantha (87% of A. mearnsii), Acacia dealbata and Acacia decurrens (each 74%) and Acacia karroo (30%). Heartwood from an underexploited PAC tannin source, Searsia lancea, taxonomically close to quebracho, shows abundant profisetinidin and catechin PACs. NMR offers the advantage of being applicable to source materials in their native state, and has potential applications in optimizing extraction processes, identification of tannin sources, and characterization of tannin content in cultivar yield improvement programmes.
authors.affiliation: Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK. dgr30@cam.ac.uk
authors.forename: David G
authors.initials: DG
authors.lastname: Reid
authors.forename: Susan L
authors.initials: SL
authors.lastname: Bonnet
authors.forename: Gabre
authors.initials: G
authors.lastname: Kemp
authors.forename: Jan H
authors.initials: JH
authors.lastname: van der Westhuizen
mesh_terms: D000045:Acacia / Q000737:chemistry*; D027926:Anacardiaceae / Q000737:chemistry*; D002396:Catechols / Q000032:analysis / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D013058:Mass Spectrometry / Q000379:methods; D015394:Molecular Structure; D024301:Plant Bark / Q000737:chemistry*; D010936:Plant Extracts / Q000032:analysis / Q000737:chemistry / Q000302:isolation & purification; D044945:Proanthocyanidins / Q000032:analysis* / Q000737:chemistry; D011748:Pyrogallol / Q000032:analysis / Q000737:chemistry; D029045:Rhus / Q000737:chemistry; D013634:Tannins / Q000032:analysis / Q000737:chemistry; D014934:Wood / Q000737:chemistry*
chemical_list: D002396:Catechols; D010936:Plant Extracts; D044945:Proanthocyanidins; D013634:Tannins; D011748:Pyrogallol; C013221:proanthocyanidin
keywords: Acacia dealbata; Acacia decurrens; Acacia karoo; Acacia mearnsii; Acacia pycnantha; Condensed tannin; Extraction; In situ identification; Schinopsis lorentzii; Searsia lancea; Solid state NMR