Evaluation of antioxidant activity of methanol extract of Stevia rebaudiana Bertoni and investigation of this properties in dairy dessert

Background and objectives: Stevia rebaudiana Bertoni, is an ancient perennial shrub of South America, with a great potential as a crop for the production of high-power natural sweetener. Due to its chemical composition and content of the phytochemical compounds, it is suitable as a raw material for production of functional foods. Stevioside has enormous sweetening power comparing to artificial sweeteners which are presented in various foods and beverages available in the market. This compound is about 300 times sweeter than sucrose. In this study to evaluate the antioxidant activity of water-methanol extract of Stevia rebaudiana Bertoni and its antioxidant effect in dairy desserts, phenolic compounds were extracted from its leaves by maceration in methanol.
Materials and methods: Antioxidant activity of the extracts using reducing power test, DPPH radical scavenging activity and total antioxidant capacity of extract were comparable with synthetic antioxidant BHT. Antioxidant effects of Stevia rebaudiana Bertoni extract in dairy desserts, using reducing power test, DPPH radical scavenging activity were evaluated after 1, 3, 6, 9, 12 and 15 storage.
Results: Average total phenolic compounds in the Stevia rebaudiana Bertoni extract was 10.64 grams Tannic acid per 100 grams dry matter. Evaluation of antioxidant activity of the extracts showed that DPPH free radical scavenging, reducing power, total antioxidant activity of the extracts are directly correlated with the amount of phenolic compounds. In all methods, antioxidant activity was concentration-dependent. Free radical scavenging activity of methanol extract of stevia was greater than BHT. Reducing power of BHT was higher than extracts and showed significant difference with the methanol extract. The total antioxidant capacity of BHT was much greater than the extract and showed significant difference with extract. Dessert samples containing stevia showed higher DPPH free radical scavenging activity and reducing power compared with control sample. During the sensory analysis conducted on desserts containing different percentages of Stevia rebaudiana Bertoni extract, respectively desserts containing percentage of , 0.75, 1, 0.25 due to high total acceptance and samples containing 0 percent (as control sample) and 100 percent (complete sugar replacement) was selected. Measurements of DPPH free radical scavenging and reducing power in dairy dessert showed that samples with higher amounts of Stevia rebaudiana Bertoni extract show higher DPPH free radical scavenging activity. In addition, dairy desserts containing Stevia rebaudiana Bertoni maintained high levels of free radical scavenging activity during two weeks storage, this led to a delay in fat oxidation and increasing shelf life during storage.
Conclusion: The results have shown that antioxidant capacity of Stevia rebaudiana Bertoni extract is considerable; therefore it can be used as a good source of natural antioxidants.