Assessment of in vitro antimicrobial and antioxidant activities of Broussonetia × hanjiana M. Kim

The fruit and bark of Broussonetia × hanjiana M. Kim (Kkujidaknamu, Korean paper mulberry) have been used as a resource for medicine and paper in Korea and Korean traditional paper (Hanji), made from extract of the B. × hanjiana bark, has been used to package dry foods. The present study was carried out to evaluate the in vitro antimicrobial and antioxidant activities of B.× hanjiana extract. The antimicrobial activity of four fractions of ethanol extract of the plant collected in July was evaluated through disc diffusion and minimal inhibition concentration (MIC) method against three Gram-positive strains, two Gram-negative strains, and one yeast. The ether and ethyl acetate fraction of ethanol extract from B. × hanjiana bark exhibited the highest antimicrobial activity with the lowest MIC value against the tested Gram-positive bacteria. The MIC of the hexane and ether fraction against Gram-negative bacteria was not detected in any sample extracts and the MIC was not observed against Saccharomyces cerevisiae in any fractions. The antioxidant activity of ethanol and hot water extract of the plant was evaluated by 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging assay. The ethanol extract showed relatively higher DPPH and ABTS radical scavenging activity than the hot water extract, regardless of the samples. The results of total phenolic and flavonoid contents were not consistent with the results of antioxidant activity and it shows antioxidant activity is not only affected by the polyphenol content but also can occur by some other phytochemicals. The antimicrobial and antioxidant activity was influenced by plant organ or extract solvent. These findings may confirm the potential of this plant as an antimicrobial and antioxidant agent.