Effects of gamma-irradiation on the antioxidant potential of traditional Bulgarian teas

Abstract

Food irradiation technologies are used to reduce the risk of food borne diseases by eliminating pathogenic microorganisms, prolonging shelf life and reducing storage losses by delaying ripening, germination or sprouting. However, application of irradiation in food technology can negatively influence the biologically active compounds in foods. In this research, the effect of gamma-irradiation on the antioxidant activity of Bulgarian teas was investigated. The aim of the study was to evaluate the total phenolic and tannin content and antioxidant activity of ethanolic extracts of Bulgarian herbal teas before and after gamma-irradiation. Mursalski tea (Sideritis scardica), Mashterka tea (Thymus serpyllum), Good Night tea (tea mix), Staroplaninski tea (Balkan tea mix), Trakia tea (tea mix), and Mountain tea (Planinski tea mix) were selected for this study. Gamma-irradiation was applied at the absorbed dose of 5 kGy. Antioxidant activity of nonirradiated and irradiated teas was determined by measuring antiradical activity against DPPH• and ABTS•+ and the ability to reduce ferrous ions. The highest total phenolic content was found in Mursalski tea (268 mg/g), and the highest tannin content in Good Night tea (168 mg/g). FRAP, TEAC and DPPH assays revealed that the most active samples were Staroplaninski (2.78 mmol Fe (II)/g), Planinski (0.87 mmol Trolox/g) and Planinski (0.032 mg/mL), respectively. The radical scavenging activity of irradiated tea samples was maintained after gamma-irradiation. The most interesting extract from irradiated tea studied was Staroplaninski, which demonstrated a higher antioxidant potential in the irradiated sample compared with the non-irradiated sample.