Antioxidative and antimicrobial activity of Reynoutria japonica extracts

Ethanolic (50%, v/v) extract of Reynoutria japonica Houtt. rhizome from the Banja Luka region was prepared. The dry extract was dissolved in methanol, and total phenols content, antimicrobial and antioxidative activities were determined. The total phenols content was determined using modified Folin-Ciocalteu method, the antimicrobial activity by monitoring the optical density, and antioxidative activity by the method of quenching stable free 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals by FRAP and ABTS metods. The antioxidative activity results were compared with control antioxidants: vitamin C, BHA and BHT. In order to determine the antimicrobial extract activity, E. coli, S. aureus and B. cereus were used as test microorganisms. The paper discusses the results of antimicrobial and antioxidative activeties of the R. japonica extract with respect to extract concentration as well as to total phenols content. The extract of R. japonica rhizome shows both, a significant overall antioxidant activity (29.84 mM (FeII)/g of extract) and high activity in quenching DPPH (IC50 = = 13.68 μg/mL) and ABTS+ (99.1%) radicals. It was found that the R. Japonica extract had greater impact on growth rate reduction of B. cereus, E. coli, than S. aureus, expressed in percentages of growth rate, L, 73.6, 59.3 and 52.1% respectively. The greatest decrease in total bacterial count, M, was observed in S. aureus (71.9%), while the decrease in E. coli and B. cereus was approximately equal (about 50%). The total phenols content, expressed as mg of galic acid equivalents/g of extract was 664±15. The high antioxidant and significant antimicrobial activity of the R. japonica extract determined in this work is associated with extremely high total phenols content.