Purification and characterization of hydrolysable tannins extracted from Coriaria nepalensis bark using macroporous resin and their application in gallic acid production

As an indispensable chemical raw material, tannins are widely used in industrial production. The crude tannins extracted from plants are difficult to be used directly because of their low purity. Therefore, tannins purification are particularly important. In this study, an economical and efficient method was developed for the purification of novel vegetable tannin resources from Coriaria nepalensis bark by macroporous resin. The purity of the obtained tannin was increased significantly from 32.5%-70.6% by optimal adsorption and desorption process conditions with D101 macroporous resin. The isothermal adsorption results illustrated by Langmuir and Freundlich equations showed that the adsorption of tannin with macroporous resin was in accordance with the exothermic process. Furthermore, the structure of the purified tannins was investigated by MALDI-TOF MS. The results indicate that the main structural compositions of the obtained tannins were Tri-O-galloylglucose, Tetra-Ogalloylglucose, Penta-O-galloylglucose and Hexa-O-galloylglucose. The hydroxyl and DPPH radical scavenging rates of the purified tannins at a concentration of 256 mu g mL(-1) increased to 86.33% and 89.08%, respectively. When the concentration was 512 mu g mL(-1), the reducing ability of ferricyanide to the ferrous form reached to 0.88. Moreover, the minimal inhibitory concentrations for Staphylococcus aureus and Escherichia coli were 32 mu g mL(-1), which is superior to commercial tannic acid. In addition, further application experiment results show that Coriaria nepalensis bark tannins can be effectively hydrolyzed under the action of tannase to obtain a high yield of gallic acid (53.2%).

Automated summary

An economical and efficient method for the purification of novel vegetable tannin resources from Coriaria nepalensis bark using macroporous resin was developed in this study. The purity of the tannins was significantly increased through optimal adsorption and desorption process conditions, showing improved antioxidant and antibacterial properties.