Ultrasound-assisted extraction of Allium macrostemon Bunge polysaccharides: optimization of extraction process, structural characterization and immunomodulatory effects

The traditional Chinese medicinal herb Allium macrostemon Bunge (AMB) possessed both nutritional value for consumption and health benefits. Although it was extensively used in many areas, studies on its polysaccharide fractions were still limited at present. In this study, ultrasonic-assisted extraction was adopted to prepare Allium macrostemon Bunge polysaccharides (AMBP), and three strategies including Box-Behnken design (BBD), genetic algorithm optimized back propagation neural network (GA-BP), and gradient boosting decision tree (GBDT) were separately employed to optimize the extraction parameters. Experimental results demonstrated that the GA-BP model exhibited superior data fitting and prediction performance with remarkably higher prediction accuracy compared with the BBD and GBDT models. The coefficient of determination (R 2 ) reached 0.9829, with a RMSE of 0.3086 and a MAE of 0.1717. The GA-BP model yielded the following predicted optimal conditions: temperature 50 °C, extraction time 33 min, and liquid-to-solid ratio 1:30 g/mL. The neutral polysaccharide AMBP-1 was isolated and purified by column chromatography, and its structural characterization was subsequently performed. The results indicated that AMBP-1 was a homogeneous polysaccharide with a relative molecular mass of 5.56 kDa, exhibiting an irregular sheet-like morphology, and its backbone structure was → 4)-β-D-Glcp-(1 → 6)-β-D-Galp-(1 → . Preliminary in vitro cellular assays and in vivo immunosuppressive mouse models demonstrated that AMBP-1 possessed immunomodulatory activity, and multi-omics analysis revealed potential correlations between its effects and alterations in gut microbiota, serum metabolites, and immune-related transcriptional profiles. In conclusion, this study established an efficient ultrasonic-assisted extraction process optimized by the GA-BP model, providing a reliable technical foundation for the preparation of AMBP, and laid the groundwork for the application of AMBP-1 in functional foods and nutraceuticals.