Structural and Rheological Characterization of a Sustainable Biopolymer: Arabinogalactan-Rich Mucilage from <i>Cereus hildmannianus</i>

Natural polymers are valued for their low toxicity, biocompatibility, and biodegradability. Plant mucilage, a sustainable and cost-effective source rich in sugars and bioactive compounds, forms gel-like structures in water, enabling its applications as a viscosity enhancer, stabilizer, emulsifier, and biodegradable packaging alternative. Cacti, notably Cereus hildmannianus K. Schum., are resilient crops with traditional uses in medicine, cosmetics, nutraceuticals, and wastewater treatment. In this study, we extracted mucilage from C. hildmannianus cladodes, obtaining a 24% yield and separated it into a soluble fraction (SF, 22%) and an insoluble fraction (IF, 78%), both slightly acidic (4.75 and 5.44, respectively) and gel-forming. SF contained 32% total sugars, 9% reducing sugars, and 33% protein, whereas IF had a higher polysaccharide purity (44% total sugars, 4% reducing sugars, 7% protein). Chemical characterization (GC-MS, GC-FID, 1H/13C NMR, FTIR-ATR) identified the polysaccharide as a type I arabinogalactan with a galactose backbone and arabinose/rhamnose side chains. Rheological analysis revealed pseudoplastic behavior with concentration-dependent viscosity, comparable to guar and xanthan gums, highlighting its potential for food and pharmaceutical applications.