The cuticle of the cactus Cereus peruvianus as a source of a homo-alpha-D-galacturonan

The waxy pecto-cellulosic cuticle of cladodes of the columnar cactus Cereus peruvianus (19% of the whole phytobiomass; dry wt) is a source of an alpha-D-polygalacturonic or pectic acid (35-40% yield, on a dry wt based on the wax-free pectocellulose layer). Warm EDTA/oxalate or room temperature strong acid/alkali cycles are efficient for pectic acid extraction, since divalent cation (mainly Ca2+) is a barrier to be removed within the native and compact architecture of the cuticle. Despite some molecular dispersion arising from the application of strong mineral acid in the first extraction step, the pectic material appears to be quite homogeneous and, on acid or enzymatic analyses, was shown to contain only D-galacturonic acid as its monomer. Cereus cuticle pectate (sodium salt) tends to gel above a concentration of 1%, a useful property that can be more easily obtained by the inclusion of sucrose, light addition of calcium salt, and/or mild acidification