Structural characterisation and immunomodulatory activity of exopolysaccharides from liquid fermentation of Monascus purpureus (Hong Qu)

As a traditional Chinese medicinal and edible fungus, Monascus has been widely studied for its secondary metabolites such as Monascus pigments and γ-aminobutyric acid. However, the exopolysaccharides have not been extensively studied and this has limited their food and industrial applications. In this study, exopolysaccharides isolated from the liquid fermentation of Monascus purpureus (Hong Qu) were successfully separated into two fractions (EPS-1 and EPS-2) by DEAE-Cellulose column chromatography. A possible pigment-exopolysaccharides complex was identified. The molecular structure of the polysaccharides portion was systematically investigated using the combined techniques of FT-IR, monosaccharide analysis, methylation analysis and 1D & 2D NMR. Monosaccharide compositional analysis showed that EPS-1 was composed of mannose, glucose and galactose in the molar ratio of 8:1:11, while EPS-2 consisted of six different monosaccharides, namely, rhamnose, arabinose, xylose, mannose, glucose and galactose, with the molar ratio of 2.2:1.9:1:5.6:1.9:7.7, respectively. Moreover, the backbone of EPS-1 mainly consisted of 5-β-D-Galf (31.74 wt%) and 2-β-D-Manp (17.48 wt%) with other sugar residues including 2,6-β-D-Galf, T-α-D-Manp, 6-α-D-Manp and 3,5-β-D-Galf also detected at small percentages. Furthermore, the immunomodulatory activity of EPS-1 was investigated by RAW 264.7 cell lines. The cell proliferation and pinocytosis activity, cytokines releasing, NO production and related mRNA levels all have been determined. The results indicated that EPS-1 could significantly promote cytokines secretion including IL-6, TNF-α, and IL-10 and improve expression levels of the related mRNA.