Optimization of Extraction Process, Structure Characterization, and Immunomodulatory Activity of Polysaccharides from Black Garlic

Abstract Ultrasound assisted extraction (UAE) was used to extract polysaccharides from black garlic, and the extraction process for UAE of black garlic polysaccharides (BGPs) was optimized via RSM coupled with genetic algorithm. The optimal extraction process parameters were obtained as follows: extraction time of 30 min, liquid‐to‐solid ratio of 29 mL/g, extraction temperature of 51 ℃, and ultrasound power of 418 W, and the yield of BGPs was 10.17% ± 0.14%. Subsequently, the crude BGPs were further purified by DEAE‐52 cellulose and Sephadex G‐100 to obtain a homogeneous fraction (BGPs‐1‐SG with the molecular weight of 1.37 × 106 Da) that was comprised of mannose (Man), glucuronic acid (GlcA), rhamnose (Rha), glucose (Glc), and fucose (Fuc) with a molar ratio of 40.23:71.06:2.96:85.38:7.32. Congo red and circular dichroism spectroscopy indicate that BGPs‐1‐SG has a triple helix structure. Scanning electron microscope and atomic force microscope demonstrate that BGPs‐1‐SG showed irregular structures including sheet‐like, rod‐shaped, irregular spherical structures, and aggregated in aqueous solutions. Moreover, BGPs‐1‐SG could increase viability, phagocytic rate, and NO content of RAW264.7 cells. Furthermore, BGPs‐1‐SG could promote the secretion and mRNA expression levels of IL‐1β, IL‐6, and TNF‐α. The findings can provide an important reference for the development of functional foods.