Optimisation of the azinobis-3-ethyl-benzothiazoline-6-sulphonic acid radical scavenging assay for physiological studies of total antioxidant activity in woody plant germplasm

A robust spectroscopic method for determining total antioxidant activity in aqueous extractions has been applied to tissues from diverse woody plant species, including seeds of Coffea arabica and in vitro shoots from Ribes nigrum, Picea sitchensis and Shorea leprosula. The assay involves scavenging of an ABTS [2,2′-azinobis-(3-ethyl-benzothiazoline-6-sulphonic acid)] radical generated by the reaction of potassium persulphate with ABTS to produce an ABTS●+ chromophore (λ = 734 nm). Antioxidants reduce ABTS●+ back to ABTS with a concomitant decrease in absorbance. Aqueous extractions from C. arabica and S. leprosula had considerably higher (110-205 μmol Trolox eq. g-1 FW) total antioxidant activities than P. sitchensis and R. nigrum (6-11 μmol Trolox eq. g-1 FW). Further studies in two of these species showed that the inclusion of water-insoluble polyvinylpyrrolidone during aqueous tissue extraction enabled the combined phenolic and alkaloid antioxidant activity to be determined. These fractions accounted for 85% and 60% of total antioxidant activity for C. arabica seeds and R. nigrum shoots, respectively. The ABTS radical scavenging assay is presented herein as a robust method for determining total antioxidant activity in germplasm from diverse woody plant tissues and species. Its applicability to study oxidative stress in tissue cultures and germplasm employed in plant biotechnology, breeding and stress physiology programmes is discussed.