In Vitro Antioxidative and Antibacterial Activities of Polyphenols in Quercus variabilis Bl. Acorn Shell
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Abstract:
In order to develop the functional ingredients from acorn shell, the functional characteristics of polyphenols in Quercus variabilis Bl. acorn shell from the Qinba Mountain area in China were investigated by solvent extraction, chemical qualitative analysis, spectral analysis, in vitro free radical scavenging assay and antibacterial activity analysis. The results showed that crude polyphenol extract (up to 4.39%) could be obtained from the acorn shell. The crude extract was further separated into three fractions by ethyl acetate, n-butanol and water extractions, which were all proven to be polyphenols containing phenolic hydroxyl group, carbonyl group, aromatic C=C skeleton, C-H bond and C-O-C bond structure, by UV-vis and IR spectral analyses. The HPLC analysis showed that the ethyl acetate extract mainly had ellagic acid, containing 4 kinds of phenols. The n-butanol extract contained 11 kinds of phenols such as ferulic acid, ellagic acid, gallic acid, epigallocatechin gallate, catechin, chlorogenic acid, epicatechin, protocatechuic acid, caffeic acid, epicatechin gallate and kaempferol. The water extract had the highest content of ferulic acid, along with 4 kinds of phenols. The DPPH free radical scavenging capacity was in the order of Vc>water extract>n-butanol extract>crude extract>ethyl acetate extract. The ABTS+ free radical scavenging capacity was in the order of Vc> n-butanol extract>water extract>ethyl acetate extract>crude extractive. The hydroxyl free radical scavenging capacity was in the order of Vc>water extract>crude extract>n-butanol extract>water extract. The crude extract and its derived three fractions exhibited different degrees of antimicrobial activity against Staphylococcus aureus, Listeria monocytogenes, Escherichia coli and Salmonella i.e. ethyl acetate extract>n-butanol extract>crude extract>water extract. These results indicated that the acorn shell is rich in polyphenols, and the polyphenols belong to different classes and exhibit strong antioxidant activities and broad-spectrum antibacterial activities.
