Macroporous-resin decolorization alters structure and bioactivity of Scutellaria baicalensis polysaccharides

The decolorization process of Scutellaria baicalensis polysaccharide (SBP) by macroporous resin was optimized through response surface methodology. The crude SBP (SBP-C) and decolorized SBP (SBP-D) were then structurally characterized by UV, high performance liquid chromatography (HPLC), gel-permeation chromatography (GPC), Fourier transform infrared spectrometer (FTIR), NMR, scanning electron microscopy (SEM), zeta potential, particle size, and thermogravimetric analysis. Their functional properties were evaluated in vitro and by fluorescence spectroscopy, with correlation analysis used to reveal the structure-activity relationship. The results showed that HPD-600 resin exhibited the best decolorization effect under optimal conditions: temperature 38°C, resin dosage 8 g, pH 3.4, and time 2.9 h. After decolorization, the total sugar content and the levels of glucose/arabinose/galactose increased significantly ( p < 0.05), while protein content decreased ( p < 0.05). Low molecular weight polysaccharides (3600–3300 g/mol) were retained, showing a predominantly multi-helical α / β -(1→4) structure with good thermal stability. Particle size and zeta potential decreased by 32.26% and 52.36%, respectively, and the microstructure transitioned into looser sheet-like helical stacks with elevated methyl-esterified galacturonic acid. These alterations improved water stability, moisture absorption, water/oil holding capacity, good emulsifying ability, and enhanced antioxidant and hypoglycemic activities. The IC₅₀ values for scavenging 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydroxyl radicals and for inhibiting α -amylase and α -glucosidase were 0.19, 0.25, 0.73, and 0.24 mg/mL, respectively. Fluorescence spectroscopy indicated that SBP non-competitively inhibited α -glucosidase and α -amylase via static quenching, with SBP-D showing enhanced efficacy. The preferred decolorization process serves as a promising purification strategy to obtain SBP with desirable functional properties, making it a potential candidate ingredient for functional foods, nutritional products, and other health-related applications.