A Novel Laboratory Method for the Extraction of Black Wattle (Acacia Mearnsii De Wild.) Bark Constituents

Abstract

Tannins are the major extractable component of black wattle (Acacia Mearnsii de Wild) bark. In a wattle factory, extracted tannin levels are one of several quality parameters (Extraction efficiency and insoluble content are some of the other parameters) that are monitored, typically using a modified Soxhlet/ reflux extraction method. However, this method is slow and laborious, and the extracted product is unsuitable for tannin color analysis, which is another important product quality parameter. A new method was then developed, aiming to measure both the conventional bark parameters as well as the color of the extract solution, and increase sample throughput. The effect of oven-drying versus freeze-drying was compared as a method of moisture removal for tannin color preservation prior to extraction. Sample filtration methods, extraction times, and chemical additives were also tested, compared, and optimised as necessary. Suitably processed bark samples were subjected to four extraction methods, i.e., Soxhlet, cold water, pressure cooker, and autoclave extractions. Extract properties were analysed using the standard Society for Leather Technologists and Chemists (SLTC) methods. Freeze- drying was shown to arrest color development in the bark. Deionisedwater was the best  extractant tested, although the addition of ethylenediaminetetraacetic acid (EDTA) enhanced the color of the extracts. The autoclave extraction method, involving two extractions and centrifugation, was found to be the most practical and effectivefor wattle bark. It  minimizes color change, reduces sample analysis variability, and allows for high sample throughput. This method is valuable for future research on wattle bark properties and for routine quality analysis in wattle extract factories.