Pectins from waste of prickly pear fruits (Opuntia albicarpa Scheinvar ‘Reyna’): Chemical and rheological properties

Low methoxyl pectin was extracted from prickly pear fruit (Opuntia albicarpa Scheinvar ‘Reyna’) by sequential extraction with water in presence of a sequestering agent. Sugar composition of the prickly pear pectin (PP) was (mg g−1, dry weight): 654 galacturonic acid, 195 galactose, 21.6 rhamnose, 1.2 arabinose and 1.2 glucose. The weight-average molecular weight was 10.16 × 105 g mol−1, the number-average molecular weight was 9.10 × 105 g mol−1 and the polydispersity index was 1.116. The FTIR spectrum of PP showed good agreement with that of standard citrus pectins and the degree of esterification of PP was 30.7%. Pectin dispersions in the range of 5–20 g kg−1 showed a non-Newtonian rheological behaviour which had good fitting to the Cross equation. The gelling ability of PP was evaluated by dynamic oscillatory rheometry. The addition of Ca2+ (0.25–0.75 mM) to 4 g L−1 PP dispersions led to the gel formation.