Optimizating the use of hydroalcoholic extract of Tetraselmis suecica algae in reduction of yellowfin tuna oil oxidation using response surface analysis

The aim of this study was to optimize the extraction conditions of hydroalcoholic extract of Tetraselmis suecica under 50, 70 and 90°C, duration 20, 70 and 120min and dry matter to solvent ratio of 10, 20 and 30 mL/g.  The effect of adding hydroalcoholic extract of Tetraselmis algae at concentrations of 0, 350, 550 and 1000ppm to Thunnus albacares oil were investigated during 56 days of storage as well. The highest percentage of free radical scavenging of 69.19% was measured at 120min, extraction temperature of 50°C and ratio of 30 mL/g solvent to dry matter. The hydroalcoholic extract of Tetraselmis contained 25.15 mg/g GAE phenolic compounds and 0.85±0.05mg/g QE flavonoid compounds, respectively. The highest antioxidant power was measured at a concentration of 1000ppm of hydroalcoholic extract of Tetraselmis algae (81.14±0.16 %) which was higher than the antioxidant power of BHT with a concentration of 0.01% (60.24±0.18%). The control treatment had the highest and the yellowfin tuna oil treatment containing 1000ppm hydroalcoholic extract of Tetraselmis had the lowest level of oxidation indices (peroxide, thiobarbituric acid and p-anisidine). The results of kinetic experiments, protective factor, antioxidant power and induction period (IP) in all three concentrations of hydroalcoholic extract of Tetraselmis were higher than control and BHT. The results showed that treatments containing three concentrations of 350, 550 and 1000ppm hydroalcoholic extracts of Tetraselmis algae had a higher protective factor and antioxidant power compared to BHT and this extract could replace synthetic compounds.