Yeast β-1,3-glucan production by an outer membrane β-1,6-glucanase: process optimization, structural characterization and immunomodulatory activity

The beta-glucan from Saccharomyces cerevisiae is a potent adjuvant that exhibits a broad spectrum of biological activities and health benefits, and different processes have been established to prepare active beta-glucan from yeast. However, studies concerning the effect of beta-1,6-glucanase enzymolysis on the structure and immunomodulatory activity of yeast beta-1,3-glucan are scarce. In this study, we aim to develop a novel enzymatic process for the preparation of immunologically active beta-glucan (BYG) from baker's yeast using a beta-1,6-glucanase GluM. The beta-1,6-glucan in fungal cell wall was specifically hydrolyzed by GluM, and resulted in cell wall decomposition and beta-glucan release. Batch production of BYG was realized with 17.8% yield, 85.3% purity and 75.4% recovery rate. Structural characterization indicated that BYG exhibits rod-like structures with natural triplex and nanoparticle-like substructures compared with the commercial Glucan 300. BYG ameliorated inflammation in a DSS-induced mouse model of colitis through inhibiting oxidative stress (NO, MDA and MPO), inflammatory mediators (NLRP3, ASC, caspase-1, iNOS and COX-2), and pro-inflammatory cytokines (IL-1 beta, IL-6, TNF-alpha, IFN-gamma), increasing the expression levels of tight junction proteins (ZO-1, occludin and claudin-1) and modulating the production of gut microbiota-synthesized SCFAs compared to the control. Our results showed that yeast beta-1,3-glucan prepared with beta-1,6-glucanase exhibits structural integrity that is responsible for its favorable immunomodulatory activity.