Methods for Extraction and Characterization of Tannins from Some Acacia Species of Sudan

Abstract

The study is aimed to analyze and compare extraction methods of tannins from three common Acacia species of Sudan. The Acacia species selected were Acacia nilotica, Acacia seyal and Acacia senegal. Bark samples from bulk collections of the three Acacia species were extracted with water, 80% methanol and 70% acetone. Two sets of extraction were made, one by boiling and a second by shaking the samples in the respective solvents for eight hours at room temperature. Although the amount of material extracted by these two procedures did not differ greatly (P > 0.05), 70% acetone was a more efficient solvent than either water or 80% methanol. The tannins of mature fruits extract of Acacia nilotica were identified by using Thin Layer Chromatography (TLC), Ultraviolet and Infrared spectroscopy. Comparisons of absorption spectra and TLC of the reference tannins and some phenolics with that of Acacia nilotica extracts revealed the presence of both condensed and hydrolyzable tannins, since it consists of catechin, tannic and gallic acids. Catechin considered to be the phenolic precursor of condensed tannins. Hydrolysis of Acacia nilotica extract, tannic and gallic acids by butanolic-hydrochloric acid yielded gallic acid which is considered to be a chemical precursor of hydrolyzable tannins.