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 β‑glucan (YG1) was obtained by drying and defatting the crude β‑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 β‑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 β‑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) from 4590 to 31.61 kDa and low polydispersity index (M/M of ~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 = 2496 kDa) exhibited the highest cell viability of 145.8 ± 4.3% at a low concentration of 1.56 μg/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.