Water-soluble yeast β-glucan fractions with different molecular weights: Extraction and separation by acidolysis assisted-size exclusion chromatography and their association with proliferative activity

Pure yeast beta-glucan (YG1) was obtained by drying and defatting the crude beta-glucan from Saccharomyces cerevisiae. The YG1 structure was characterized by total sugar content, protein content, FT-IR spectroscopy and monosaccharide composition analysis. Different molecular weight fractions of water-soluble yeast beta-glucan (WYG) were prepared by extraction with 2.0 M NaOH, degradation of the insoluble residue with 1.0 M HCl based on single-factor experiments, and fractionation on a size exclusion chromatography column (SEC, Sephacryl S-400). The molecular sizes of as-obtained fractions were measured by multi-angle laser light scattering combined with SEC and differential refractive index detector (SEC-MALLS-RI). Results indicated that YG1 had a high purity and was almost composed of beta-D-glucose (97.71%) except trace mannose. The WYG yields by alkali extraction and acidolysis were 12.41% and 42.85%, respectively. Fourteen fractions with molecular weight (M-w) from 4590 to 31.61 kDa and low polydispersity index (M-w/M-n of similar to 1) were successfully separated, showing high recovery rates of 61.9-92.5%. Additionally, these fractions could promote the proliferation of RAW264.7 macrophages, and the fraction (M-w = 2496 kDa) exhibited the highest cell viability of 145.8 +/- 4.3% at a low concentration of 1.56 mu g/mL. This work not only provides an efficient method for separating WYG fractions with different molecular weights and low polydispersity, but also lays a theoretical basis for interpreting the relationship between molecular size and bioactivity. (C) 2018 Elsevier B.V. All rights reserved.