Song Xiaoyong^1,, Cheng Luming²

This study assessed polyphenol compositions, antioxidant and antimicrobial characteristics of blueberry-leaf extracts. Four different solvents (70% acetone, 100% methanol,50% and 95% ethanol) were applied. Results showed phenolic compounds were identified as quercetin, kaempferol, gallic, protocatechui, caffeic, vanillic, syringic, p-coumaric andferulic acids. Caffeic acid was the foremost component in 50% ethanol, 70% acetone and methanol extracts, whereas protocatechui acid was the major compound in 95% ethanol extracts. The methanol extracts showed the highest total phenols, tannin and DPPH scavenging activity, and the 50% ethanol extracts had the greatest reducing power and ORAC values. The lowest contents of total phenols and tannin were in 95% ethanol and 70% acetone extracts, respectively. All extracts demonstrated the antimicrobial activity against E. coli, L.monocytogenes, S.typhimurium, S. aureus and fungi, except for the 95% ethanol extract against L.monocytogenes. The 50% ethanol extracts showed the highest inhibitory effect against S. aureus with the lowest minimum inhibitory concentration (MIC) against all tested microbes. The greatest inhibition zone and the smallest MIC against fungi were found in the 95% ethanol and methanol extracts. These results indicated that the blueberry leaves are good source of polyphenols and could be used as natural antioxidant and antimicrobial agent.

blueberry leaf, extraction solvent, polyphenols, antioxidant property, antimicrobial activity