LAUSR

Abstract Acetylated-low methoxyl pectins were isolated from sweet prickly-pear (Opuntia albicarpa) and ‘xoconostle’ or acidic prickly-pear (O. matudae), by sequential extraction with water in presence of ethylenediaminetetraacetic acid as sequestering agent. The extraction protocol resulted in the isolation of pectins of good enough purity as evidenced by their high galacturonic acid contents (65.23 and 75.72% w/w, for sweet prickly-pear pectin (PP) and xoconostle pectin (XP), respectively). Both pectins had an important protein content (10.82 and 2.58% for PP and XP, respectively) and they can be described as acetylated-low methoxyl pectins. Degree of methoxylation (DM) and degree of acetylation (DA) values for PP were 26.83 and 21.83%, respectively. XP showed DM and DA values of 45.62% and 4.94%, respectively. Weight-average molecular weight (Mw) values of 204.08 and 161.73 kDa were determined for PP and XP, respectively. Pectin aqueous dispersions showed a non-Newtonian rheological behaviour which had good fitting to the Cross equation. The viscoelastic behaviour of 1%-pectin-calcium systems exhibited a predominantly solid-like character, the presence of 1 mM CaCl2 was enough to the formation of soft gels, the further increase of Ca2+ ions (3 and 5 mM) yielded the formation of soft and elastic gels. The viscoelastic solid behaviour of PP gels was more dominant than that of XP gels. The high content of acetyl groups did not have negative effect on the gel formation ability of both, PP and XP.