Pectins from Opuntia spp.: A Short Review
Two distinctive water-soluble high-molecular-weight pectic polysaccharide materials that occur in Opuntia cladodes and fruits have been extracted and studied in their chemical and rheological properties in our laboratory, namely, the well-known mucilage and a calcium-sensitive gelling fraction. Mucilage is present in the characteristic slimy fluid secreted by cladodes and fruits and it does not gel in the presence of calcium. Pectin of low degree of methoxyl occurs in the cell wall and can be extracted using a mild alkali process aided with a chelating agent. It shows remarkably good gelling properties in the presence of CaCl2 by a cooperative Ca2+ “egg-box” binding mechanism. Although both materials share similarities in the composition profile of their neutral constituent sugar residues, pectin has a significantly greater amount of linear polygalacturonic acid. This difference causes very different physicochemical and functional properties underlying the potential applications of these polysaccharides in a wide variety of fields (e.g., foods, biotechnology, medicine).