Physicochemical properties of South African prickly pear fruit and peel: Extraction and characterisation of pectin from the peel

Abstract

Abstract The aim of this study was to determine the physicochemical properties, extract and characterise pectin from green (Morado), purple (Algerian), and orange (Gymno carpo) varieties of South African prickly pear (PP) (Opuntia ficus-indica) fruit peel. Pectin was extracted using sulphuric acid at four different pH levels (1, 2, 3, and 4) and three different microwave power levels (low 300 W, medium 400 W, and high 500 W) at a fixed time of 10 min. Yield of pectin for purple ranged from 2.9 to 13.8%, orange from 1.4 to 9.8%, and from 2.3 to 10.0% for green prickly pear peel (PPP). Maximum yield of 13.8% on purple, 10.0% on green, and 9.8% on orange was obtained at pH 1.0 and medium power level. Ash content of the extracted pectin was significantly high at 25.16, 34.26, and 36.30% for green, orange and purple PPP, respectively. However, pectin showed lower moisture content and equivalent weight. The methoxyl contents were 2.28, 2.38, and 3.86%, for anhydrouronic acid contents were 25.58, 25.93, and 38.84%, and degree of esterification was 49.87, 50.63, and 56.39% across the orange, purple, and green varieties. The PPP pectin spectra exhibited similarities in their absorption pattern to that of commercial citrus pectin.