Structural Characterization and Prebiotic Effects of Curcuma kwangsiensis Polysaccharide-Zinc Complex

This study investigated the prebiotic potential of polysaccharides isolated from Curcuma kwangsiensis and their zinc complex. A water-soluble polysaccharide fraction (WPCK) was extracted from C. kwangsiensis and subsequently complexed with zinc to yield WPCK-Zn. The physicochemical properties of WPCK-Zn, including zinc content, total carbohydrate content, protein content, and aqueous solubility were systematically characterized. Structural features were elucidated using ultraviolet–visible spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy (SEM), and Zeta potential analysis. In vitro digestibility was assessed under simulated salivary, gastric, and intestinal conditions to evaluate resistance to enzymatic degradation. Prebiotic activity was determined by measuring the proliferative effects of WPCK and WPCK-Zn on four representative probiotic strains: Lactobacillus brevis GIM1.773, Lactobacillus plantarum GIM1.191, Lactobacillus delbrueckii sub sp. bulgaricus GIM1.155, and Streptococcus thermophilus GIM1.540. Results indicated that WPCK-Zn exhibited a total carbohydrate content of 70.45% and a protein content of 0.19%, both lower than those of native WPCK; its zinc content was 29.39 mg/g. Spectroscopic and microscopic analysed confirmed retention of core polysaccharide architecture, including characteristic functional groups and a triple-helix conformation. SEM revealed a more homogeneous and smoother surface morphology for WPCK-Zn relative to WPCK, accompanied by enhanced thermal stability and an increased absolute zeta potential value. Both WPCK and WPCK-Zn existed in an amorphous crystalline state. In vitro digestion assays demonstrated robust resistance to gastrointestinal degradation for both samples, supporting their bioavailability to colonic microbiota. Prebiotic evaluation revealed dose-dependent stimulation of all four probiotic strains, with WPCK-Zn consistently outperforming WPCK—particularly at 2% (w/v), where it significantly enhanced proliferation of L. brevis, L. plantarum, and S. thermophilus. Polysaccharide-Zinc complex from Corydalis kwangsiensis shows potential as a novel zinc supplement, providing a theoretical basis for the application of Corydalis kwangsiensis polysaccharides and their metal complexes in functional foods or microecological preparations.