Structural properties of Bletilla striata polysaccharide and the synergistic gelation of polysaccharide and xanthan gum

Bletilla strata polysaccharide (BSP) has been attracting increasing attention because of its numerous bioactive components. In this study, BSP was obtained by water-extraction and ethanol-precipitation, and its structure and synergistic interaction with xanthan gum (XG) were then investigated. BSP was identified as a highly linear polymer with a weight average molecular weight (Mw) of 323.7 kDa, whose ratio of mannose to glucose was 2.4:1.0. BSP had the backbone of →4)-β-Manp-(1→, →4)-β-Glcp-(1→, as well as a small amount of →3)-β-Manp-(1→, terminated by T-Manp residues. Moreover, it was also substituted by a small number of O-acetyl groups at C-3 position of →4)-Manp-(1→ residue. Despite the poor gelling ability of BSP itself, it could form a firm and thixotropic gel when mixing with xanthan gum (XG). Upon cooling, irrespective of the mixing ratio, all BSP/XG mixtures exhibited a steep increase in G′ at ∼60 °C, which was defined as the onset temperature of the synergistic gelation. On heating, all gels melted at 60 °C, without detectable thermal hysteresis. The most pronounced synergistic interaction occurred at BSP/XG ratio = 5:5. Overall, this study provides new knowledge about the structure of BSP and its synergistic interaction with XG. Especially, the thixotropy of the mixed gels may find usefulness in formulating easy-to-swallowing food products.