Ultrasound assisted aqueous two-phase extraction of polysaccharides from corn stigma: Process optimization, structure characterization, and immunomodulatory activity

The two models of ultrasound assisted aqueous two-phase extraction (UATPE) of polysaccharides from corn stigma were established by response surface methodology (RSM) and artificial neural network (ANN), and compared the prediction ability of RSM and ANN models. Subsequently, the extraction process of corn stigma polysaccharides (CSPs) was optimized by the combination of genetic algorithm (GA) and ANN. The results show that two models could precisely predict the CSPs yield, whereas the prediction ability of ANN was better than RSM. The optimum combination of process parameters was as follows: the ultrasound power of 466 W, extraction temperature of 54 C-degrees, liquid-to-solid ratio of 47 mL/g, and extraction time of 31 min. The highest CSPs yield was 9.89% +/- 0.14% under the above parameters, and then the crude CSPs were further purified by DEAE-52 and Sephadex G - 100 chromatography to obtain a homogenous fraction (CSPs-2-SG with a molecular weight of 2.86 x 10(6 )Da) that consisted of Man, GlcA, GalA, Glc, Gal, and Xyl with a molar ratio of 9.14:16.35:11.27:91.08:6.49:4.71. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) demonstrated that CSPs-2-SG showed irregular structures including uneven fragments, some holes, and spherical aggregates on the surface. Finally, the immunomodulatory activity of CSPs-2-SG was evaluated by RAW264.7 cells. CSPs-2-SG could improve viability, phagocytic rate, and NO content of RAW264.7 cells. Moreover, CSPs-2SG could increase the levels of IL - 1 beta, IL-6, and TNF-alpha in RAW264.7 cells. The findings provide important references for utilizing corn stigma as a potential natural immune regulator.