In vitro antioxidant and antibacterial potential of tea leaves harvested from small tea plantations of sub-Himalayan Terai region

Abstract

Tea has long been praised for its antioxidant and antimicrobial properties and other biological activities. In this research, we collected the leaves of ten different tea clones from small tea growers in the sub-Himalayan Terai region of West Bengal, India. Most of the collected samples were Toklai Vegetative (TV) tea clones established by the Toklai Tea Research Institute; some Garden-series clones were also included. Samples were extracted using three different solvents based on a wide range of polarity: petroleum benzene, acetone and methanol. Extracted samples were tested for in vitro antioxidant activity using DPPH (2,2-Diphenyl-1-picrylhydrazyl) assay, Nitric Oxide (NO) assay and Ferric Reducing Power (FRP) assay. Antibacterial activity against four pathogenic bacteria was tested using agar well-diffusion method. Results clearly showed that tea clones used by small tea growers in Terai are potentially bioactive. Moreover, TV9, which is originally a Cambod tea clone, performed better than all other samples in all tests. Of the non-polar extracts, AV2 recorded the best results, which confirms the biological active potential of its non-polar volatile aroma imparting molecules. Given that AV2 is a China-type Darjeeling tea clone, this result is valid and assuring. Total phenol and flavonoid quantification were also assessed. TV1 (an Assam-China hybrid) and TV9 again showed significant results. For a detailed antioxidant evaluation, fractionation by column chromatography was done with two of the best samples selected upon results of preliminary antioxidant analysis. Fractions of clones exhibited variable antiradical activity with changes in solvent’s polarity. However, further detailed and more comprehensive studies on biochemical analysis, using tools of metabolomics to evaluate which components of tea clones are responsible for bioactive properties, are needed.