Antioxidative and Antibacterial Activity of Polyphenols in Quercus variabilis Acorn Nutlet

Quercus variabilis acorn nutlet from Qinba mountainous region in China was extracted by solvent extraction,and the components of polyphenols in the acorn nutlet were investigated by microporous resin separation,UV spectrum,IR spectrum and HPLC analysis. The antioxidative and antibacterial activity of the purified extractives from the acorn nutlet were also evaluated to by scavenging abilities of DPPH free radicals and ABTS⁺ free radicals and inhibition zone. Results showed that the crude polyphenols of acorn nutlet could be extracted up to 20.5%(345 mg/g gallic acid).Purified polyphenols was up to 34% obtained by D4020 microporous resin isolation(702 mg/g gallic acid). By UV-vis spectra and IR spectrum analysis,the purified polyphenols were proved to have phenolic hydroxyl group,carbonyl group and aromatic C=C skeleton structure. HPLC analysis showed that the purified acorn nutlet polyphenols contained at least 28 compounds,including protocatechuic acid,caffeic acid,ferulic acid,ellagic acid,quercetin and kaempferol. The contents were 24.9,14.6,3.2,2.2,0.5,0.2 mg/g. The IC₅₀ values of scavenging DPPH free radicals of acorn nutlet polyphenols and V_C were 2.50 and 3.20 μg/mL,the IC₅₀ values of scavenging ABTS⁺ free radicals were 28.67,28.82 μg/mL. The ability to scavenge DPPH free radicals,ABTS⁺ free radicals and Fe³⁺ were similar to that of control V_C. The ferrous ions chelating ability was much lower than that of EDTA-2Na. The anti-lipid peroxidation ability could be comparable to V_C. The crude extractives and purified extractives all had strong inhibitory effect on Kazakhstan,Salmonella,Staphylococcus aureus and Escherichia coli but weaker inhibitory effect on Listeria. Results revealed that the Quercus variabilis acorn nutlet was rich in polyphenols,the acorn nutlet polyphenols had strong antioxidant activity and broad-spectrum antimicrobial activity,which would be good materials for developing health products and natural antimicrobial agents.