Physicochemical properties and antioxidant activities of white dragon fruit peel pectin extracted with conventional and ultrasound-assisted extraction

The objective of this study was to investigate the optimal condition for extracting dragon fruit peel (DFP) pectin with the best physicochemical properties and high antioxidant activity by using conventional extraction (CE) and ultrasound-assisted extraction (UAE). DFP was extracted using CE and UAE method at 45, 60 and 75 degrees C for 30 and 60 min. In this study, UAE significantly improved antioxidant activity of the extracted DFP pectin when comparing to CE. DFP extracted with UAE at 45 degrees C for 30 min had the highest antioxidant activity (51.58 +/- 0.30 by DPPH, 39.81 +/- 1.43 mgGAE/100 g by ABTS) (p < 0.05). Moreover, UAE also increased the production yield of sample at 45 degrees C for 30 min (9.38 +/- 0.50%) (p < 0.05) which was higher than the treatments with CE. The chemical properties of DFP pectin including equivalent weight, degree of esterification, methoxyl content and total anhydroronic acid revealed that DFP pectin could be categorized as low-methoxyl pectin. Present study demonstrated that DFP pectin was an ideal alternative source of pectin with high antioxidant activity compared with commercial citrus pectin. The optimal condition for extraction of pectin by UAE was at 45 degrees C for 30 min which could be established as a potential method to extract pectin from DFP for industrial scale.