Non-methylesterified pectin from pitaya (Hylocereus undatus) fruit peel: optimization of extraction and nanostructural characterization

Abstract

The peel of pitaya fruit is a promising source of pectin, and non- or low-methylesterified pectin has multiple bioactivities and application scenarios. In this study, non-methylated pectin was prepared from pitaya peel and the structure was characterized. Single factor experiment and response surface methodology were conducted to optimize the procedure of ultrasonic-assisted extraction for pectin. Under the optimal conditions (solid-liquid ratio of 1:40 g·mL−1, extraction temperature at 56 °C, extraction time of 25 min and ultrasonic power of 200 W), the pectin yield was up to 9.93% ± 0.97%. Degree of methylesterification and FTIR analysis confirmed that the extracted pectin was almost non-methylesterified. The pectin possessed less linear homogalacturonan (HG) but more rhamnogalacturonan (RG) regions according to the molar ratios of monosaccharides. Meanwhile, the molecular weight of the pectin was 33.52 kDa and the crystalline index was only 0.60%. Furthermore, the nanoscale structure observed by atomic force microscopy showed that the pectin was rich in highly branched polymers. Generally, pitaya peel pectin extracted by ultrasonic-assisted extraction showed a wide range of potential use as a non-or low- methylesterified pectic substance to reach the efficient utilization of fruit waste.

Keywords

• dragon fruit
• response surface methodology
• ultrasonic-assisted extraction
• structure