Chemical, thermal, morphological, and rheological characterization of mucilage from different cactus pears cultivars (Opuntia spp.)

Abstract

The mucilage from the cladodes of cactus pear (Opuntia spp.) is a hydrocolloid complex of carbohydrates with highly branched structures and high molecular weight, which serves to prevent structural contraction by facilitating the formation of a continuous matrix. The aim of the present work is to compare the chemical, thermal, morphological, and rheological characteristics of different mucilage from cultivars of Opuntia spp. to understand the complexity of mucilage because its composition and properties vary depending on the cultivars and plant species. The parenchyma from the different cultivars was chopped and rested in water, after which the mucilage was recovered by precipitating with ethanol. The chemical composition revealed protein values ranging from 7.5 to 10.4%, with significant differences observed between cultivars. However, there were no significant differences in the lipids, carbohydrates, or humidity values. The X-ray diffraction patterns (XRD) showed the crystalline structures of minerals such as calcium carbonate (CaCO3), with distinct patterns also observed for the cultivars “milpa alta” and “reyna”. The proton nuclear magnetic resonance (1H NMR) identified carbohydrates as α-arabinose, β-xylose, β-galactose, and α-galactose, with the cultivar “xoconostle de invierno” showing the highest concentrations. Additionally, in the cultivars “milpa alta” and “COPENA V1”, the Fourier-transform infrared spectroscopy (FTIR) revealed bands related to -OH, -C-O, and -C-C-C functional groups, which are fingerprints of the polysaccharides. Thermogravimetric analysis (TGA) showed three weight loss events at 140, 250, and 460 °C related to carbohydrate degradation in the five cultivars evaluated. The different mucilages analyzed showed similar compounds and chemical structures but different concentrations. The mucilage of “cristalina” and “COPENA V1” cultivars showed the highest viscosity and maintained their rheological properties despite changes in temperature and shear rate.