Effects of cold plasma on Stevia rebaudiana Bertoni antioxidant activity

Abstract

Studies conducted over the past three decades have demonstrated that cold plasma (CP) can be a sustainable tool for enhancing various traits in plants (seed germination, seedling growth, secondary metabolites). We have recently demonstrated that pre-sowing Stevia rebaudiana Bert. seed treatment with CP can substantially increase the concentration of natural sweeteners - steviol glycosides. However further research is needed to fully understand the underlying mechanisms and cumulative changes in biochemical and physiological processes induced by CP. The aim of this study was to determine the CP-induced effect in stevia on antioxidant activity and antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT)) activity. Stevia seeds were treated with dielectric-barrier discharge (DBD) and capacitively coupled (CC) CP for 2, 5 and 7 min. The antioxidant activity measured in stevia leaves as DPPH scavenging capacity was increased in DBD7 group by 1.14 folds compared to the control; however, decreased in CC2 and CC7 groups, by 4.51 and 1.79 folds respectively. Antioxidant activity was consistent with the phenolic compounds increase. In addition, an increase in CAT activity by 3.5 folds in DBD5 group was also consistent with antioxidant activity. However, SOD activity changes compared to the control group did not correlate with other results: CC groups showed a tendency of increased activity but decreased in DBD5 and DBD7 groups. It could be due to the CP effect on overall phytochemical composition changes. In conclusion, seed treatment with DBD increased antioxidant activity in stevia which correlated with phenolic compounds and CAT activity rather than SOD activity.