Development of antioxidative red dragon fruit bar by using response surface methodology for formulation optimization.

Optimization of ingredient levels in red dragon fruit bar was conducted using response surface methodology (RSM). The central composite design (CCD) was used to establish the formula based on two independent variables, including levels of passion fruit and pectin. Total titratable acidity (TTA), ascorbic acid (AA), betacyanin (BA), total phenolic content (TPC), flavonoid content (FC), antioxidant activity (DPPH radical scavenging activity), color (L*-, a*-, and b*- values), and sensory evaluation (overall likeness score) were monitored. It was found that second-order regression models fitted for all responses where the optimum levels of passion fruit and pectin for mixed red dragon-passion fruit bar with desirable characteristics were 29.63% and 1.35%, respectively, based on desirable characteristics. The corresponding optimum values of TTA, AA, BA, TPC, FC, and DPPH radical scavenging activity were 2.30%, 0.0189%, 49.34 mg/100 g, 0.33 mg GAE/g, 75.29 mg QE/g, 11.46%, respectively. L*-, a*-, and b*- values...