Antioxidant Effects of Stevia rebaudiana Leaf and Stem Extracts on Lipid Oxidation in Salted Pacific Saury (Cololabis saira) during Processing

Abstract

Stevia rebaudiana, cultivated as a sweetener, also contains numerous phenolic compounds with strong antioxidant activities. Here, the antioxidant effects of Stevia rebaudiana leaf (SRL) and stem (SRS) extracts on lipid oxidation in salted Pacific saury (Cololabis saira) fillets throughout the salting and drying process are investigated. Fish fillets treated with SRL and SRS extracts are monitored for lipid oxidation and physicochemical characteristics. The results show that both SRL and SRS extract treatment significantly retard lipid oxidation in the fish, shown by reductions in the levels of peroxide, conjugated diene, and thiobarbituric acid reactive substances. These effects can be attributed to both the antioxidant activity of the extracts and the possible inhibition of the fish lipoxygenase by the SRL and SRS extracts. Interestingly, the SRS extract has stronger activities than the SRL extract in inhibiting lipid oxidation during the fish drying process, despite having relatively lower DPPH radical scavenging activity, ferrous ion-chelating ability, and reducing power. Notably, the SRS extract is more effective at hydroxyl radical scavenging than the SRL extract, suggesting the importance of hydroxyl radical scavenging during the fish drying process. Consequently, stevia extracts can be a source of natural antioxidants to minimize lipid oxidation in salted fish. Practical applications: Current work demonstrates the antioxidant effect of the aqueous extracts of stevia leaf and stem against the lipid oxidation in salted Pacific saury during salting and drying process. The results open the way to the potential utilization of extracts from stevia leaf and stem, a by-product of the sweetener industry, as alternative source of natural antioxidants for salted fish and meat.