Abstract
Tannins are natural polyphenolic compounds widely distributed in the plant kingdom in the leaves, bark, fruits, and other parts. They have various biological functions in humans and animals and are used mainly in the pharmaceutical and cosmetic industries. The aim of this work was to isolate, extract, purify, and identify the tannins from the root bark of a common oak tree (Quercus aegilops L.) in Jordan and around the Mediterranean. The results showed that at least one form of ellagitannin (ellagic acid ester), quercitrin, afzelechin, valoneic acid, trigalloyl glucose, and catechin was identified in addition to two unidentified compounds. Results of this work can help in developing an ESI MS/MS search library for the constituents of the tannins of oak (Quercus aegilops L.) root bark.
Highlights
Tannins are complex heterogeneous group of polyphenolic secondary metabolites of higher plants which share the ability to bind and precipitate proteins, alkaloids, and polysaccharides [1]. eir molecular weights range between 500 and 20,000 Da. [2], Okuda and Ito [3] reported that some types of tannins have molecular weights smaller than 500 Da. ey are considered to be free radical scavengers [4] which have the ability to inactivate microbial adhesions as well as enzymes, and cell-envelop and transport proteins [5]
Widsten et al have shown that tannins have antimicrobial properties due to their bacterial toxicity exerted by their o-diphenol groups which act as iron chelators [6]
Chromatographic separations for different phenolic compounds extracted with ethanol and purified on Sephadex LH20 were performed on a reversed phase HPLC
Summary
Tannins are complex heterogeneous group of polyphenolic secondary metabolites of higher plants which share the ability to bind and precipitate proteins, alkaloids, and polysaccharides [1]. eir molecular weights range between 500 and 20,000 Da. [2], Okuda and Ito [3] reported that some types of tannins have molecular weights smaller than 500 Da. ey are considered to be free radical scavengers [4] which have the ability to inactivate microbial adhesions as well as enzymes, and cell-envelop and transport proteins [5]. It is well established that the composition and concentration of tannins vary depending on species, part, and age of the plant from which they are extracted [1]. Based on their specific structures and chemical properties, tannins are classified into hydrolysable, condensed, and complex [13, 14]. Complex tannins consist of flavan-3-ol units (catechin moiety) glycosidically bound to gallotannin or ellagitannin units. They have been detected in various oak species (e.g., Quercus petraea) [1, 18, 19]. E aim of this work is to extract tannins from oak (Quercus aegilops) root bark, purify them on Sephadex LH20 column, and identify them using HPLC/MS-MS technique as this system is supplied with a library which facilitates the identification of the different tannin compounds
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