Optimization of microwave assisted extraction of dragon fruit peel pectin was conducted using respond surface methodology. Effect of extraction conditions, i.e. pH value (X1), extraction time (X2) and solid-liquid ratio (X3) on the extraction yield was investigated using a central composite experimental design. Optimization of microwave assisted extraction was performed and three-dimensional (3D) response surface plots were derived from the mathematical models. Analysis of variance (ANOVA) was conducted and indicated a significant interaction between extraction conditions (pH value and extraction time) and extraction yield. The optimum conditions of microwave assisted extraction were as follows: X1 = 2.07; X2 = 65 s and X3 = 66.57. The verification test on pectin extraction was performed and revealed a perfect agreement between experimental and predicted values. The maximum predicted yield of pectin extraction was 18.53%. Overall, application of microwave assisted extraction can give rise to high quality dragon fruit peel pectin.
In this work, oven-dried, freeze-dried and spray-dried agaro-oligosaccharide powders were characterized to investigate their physicochemical and antioxidant properties. Agaro-oligosaccharide powders were shown to exhibit high water solubility index (88.73 – 95.88%), water absorption capacity (0.96 – 2.57 g/g) and oil absorption capacity (0.40 – 0.45 g/g). Agaro-oligosaccharide powders were shown to possess moderate DPPH radical scavenging activity (10.65 – 14.59%), ABTS radical scavenging activity (44 .47 – 65.61%) and ferric reducing antioxidant activity (0.165 – 0.353). Agaro-oligosaccharide powders were further characterized with respect to thermal and pH stability. Agaro-oligosaccharide powders were shown to exhibit high temperature resistance (≤ 100oC) and acid/alkaline resistance.