Penetration of the Polyflavonoids and Simple Phenolics: A Mechanistic Investigation of Vegetable Tanning

Abstract

Mechanisms of tanning are the fundamental base for predictingand developing new tanning agents and technologies. However,many mechanistic questions remain for us, such as: How doesthe penetration happen? How do the phenolic compounds workindividually? In this study, penetration processes of the tanninextracts were investigated with the Bayberry extract(prodelphenidins), the Larch extract (procyanidins) and theAcacia Mangiumextract (prodelphenidin-procyanidincomplexes) used as tanning agents. During the process, thetanning liquids were regularly sampled and the simple phenolicsand polyflavonoids were quantified respectively with a Prussianblue assay, a conductivity analysis, an acid-butanol assay as wellas a HPLC analysis. The results showed that, during tannin, theconcentration of polyflavonoids in the tanning liquid decreasedcontinuously. In contrast, for the simple phenolics, theconcentration decreased at first and later increased. Therefore,penetration processes of the tannin extracts can be described as:in the beginning, both simple phenolics and polyflavonoidsstarted to penetrate; then the simple phenolics completed theirpenetration first and reversibly bound with collagens; in themeantime, the polyf lavonoids were still penetrating andgradually replacing those simple ones from collagen matrix; atthe end of the tanning processes, most of the simple phenolicswere replaced by the polyflavonoids, meanwhile they weremigrated back into the tanning liquids. The results will providevaluable information to help understanding the mechanism ofvegetable tanning.