Optimizing extraction conditions of crude fiber, phenolic compounds, flavonoids and antioxidant activity of date seed powder

The objective of this study was to optimize the extraction conditions of crude fiber, phenolic compounds, flavonoids, and antioxidant activity from date seeds powder, using Response Surface Methodology. A central composite design with four independent variables; concentration of ethanol (X₁ = 25, 50 and 75% v/v), solvent: sample ratio (X₂ = 40:1, 50:1 and 60:1 v/w), temperature (X₃ = 45, 55 and 65 °C), and extraction time (X₄ = 1, 2 and 3 h) and a three level face centered cube design were used. A total of twenty nine experimental runs with five replicates at the central point were used to study the response variables using two extraction cycles. Maximum phenolic compound content (71.6 mg GAE/100 g) was extracted using 50% ethanol solution with 40:1 solvent: sample ratio for 1 h at 55 °C. While the maximum antioxidant activity (55.02 µmol Fe(II)/g) was obtained using similar ethanol concentration and solvent: sample ratio except at lower temperature (45 °C) for 2 h. On other hand, the maximum flavonoids content (455.77 mg CEQ/100 g) was reached by using 50% concentration, 50:1 solvent: sample ratio at 65 °C for 3 h. In contrast, the content of fiber was not affected by the different extraction conditions. Results indicate that using combination of extracted conditions, have a great potential for extracting all depending compounds except crude fiber.