Evaluation of antioxidant activity of formulated functional drinks derived from katuk (Sauropus androgynous) leaf extracts: Optimization using response surface methodology (RSM).

Katuk (Sauropus androgynus) is one of local plants that contains high chlorophyll content and large amounts of antioxidants, which are very useful to prevent free radicals and premature aging. Katuk leaves can be directly consumed as vegetables or be processed as fermented health beverage. This study aimed to evaluate antioxidant activity of formulated functional drinks derived from katuk leaf extracts. The activity of the functional drinks was optimized by varying fermentation conditions, such as kombucha culture level, sucrose level, and fermentation time, using response surface methodology (RSM). Katuk leaf was extracted using sterile hot water (leaf:water ratio, 1:10) with concentration of kombucha culture varied from 10–20% (w/v), sucrose addition varied from 10–20% (w/v), and fermentation time varied 0-12 days. The optimization was done by using Box-Behnken Design Response Surface Methodology (RSM) to evaluate and select optimal process conditions from a combination of factor levels which results in an optimal response. Based on RSM Box-Behnken Design, it was found that the above-mentioned three factors greatly influenced the response value. Optimum conditions were obtained with culture concentration of 13.75%, sucrose addition of 20% (w/v) and fermentation time of 5.66 days with the percentage inhibition of antioxidant was 80.27% (DPPH method), Feric reducing antioxidant power was 217.78 mg ascorbic acid/mL, pH was 4.57 and total polyphenols was 1,31 mg GAE/mL and reducing sugar 20,78 mg/mL. [ABSTRACT FROM AUTHOR]