Abstract
Sphingans, a group of structurally closely related bacterial exopolysaccharides produced by members of the genus Sphingomonas, can be applied in a variety of industries such as food, cement, and personal care applications due to their high viscosity. A high sphingan-producing-bacterium, Sphingomonas sp. WG can secret large quantity of sphingan designated as WL. To enhance the production of WL, a three-stage control strategy was applied and the highest WL production can reach 33.3 g/L. The rheological analysis showed that the aqueous solution of WL had high viscosity, typical shearing-thinning behavior and great stability to high temperature, a wide range of pH (1 to 14), and high salinity. WL was composed principally of carbohydrate with 6.52% O-acyl groups. The carbohydrate portion of WL contained about 13% glucuronic acid and some neutral sugars including mannose, glucose and rhamnose in the molar ratio of 1:2.28:2.12. Partial acid hydrolysis of WL produced a new oligosaccharide WL-1. Structural resolution revealed that WL-1 consisted of α-L-Rha-(1→4)-β-L-Rha-(1→4)-β-D-Glc-(1→3)-α-D-Glc with β-D-Man substituent at the third glucose residue and carboxyl and O-acyl groups. These findings will broaden the applications of this novel sphingan in food, ink, oil and other industries.
Highlights
Sphingans, a group of structurally closely related bacterial exopolysaccharides produced by members of the genus Sphingomonas, can be applied in a variety of industries such as food, cement, and personal care applications due to their high viscosity
In order to achieve high sphingan yields, a three-stage control strategy was applied in the fermentation process of sphingan WL by Sphingomonas sp
The main controlled parameter was dissolved oxygen (DO) concentration considering that the oxygen transfer might be limited by the high viscosity of the broth in the polysaccharide production
Summary
Three-stage control fermentation and purification of the sphingan WL. In order to achieve high sphingan yields, a three-stage control strategy was applied in the fermentation process of sphingan WL by Sphingomonas sp. When the concentration of salts further increased, the viscosity decreased slightly and remained 90 and 86% when 10% (w/v) NaCl and CaCl2 was added, respectively These results showed that the WL was of good salt resistance and this might be caused by the good hydrophilicity of main chain structure of EPS that made the space structure stable even when the charge of the EPS was shielded[16]. ® tion[19] while gellan gum with low acyl content (Kelcogel F) can be used as a gelling agent in food and personal ® care applications[20] Welan gum, with both acyl group and L-rhamnosyl or L-mannosyl as side chains, does not gel but it shows excellent rheological properties and good stability over a broad range of pH (2–12) and temperature (up to 150 °C) and can be applied in petroleum, concrete, food and many other industries[21].
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