Gel properties of xanthan containing a single repeating unit with saturated pyruvate produced by an engineered Xanthomonas campestris CGMCC 15155

Abstract

Xanthan, a polysaccharide used as a viscosifier in both food and non-food industries, is produced by Xanthomonas campestris. According to the present works on the relationship between the physical properties and pyruvate content, a tailor-made high viscous/modulus xanthan (named XG-SP) containing a single repeating unit type with saturated pyruvate group was produced by an engineered strain XM (ΔFG, pBBRL). XG-SP was a weak gel at a concentration of 0.3% without heat treatment, and its storage modulus (G′) was largely independent of frequency. XG-SP hydrogel showed higher viscosity and more excellent salt-tolerance property than the natural xanthan. XG-SP also exhibited self-supporting properties at a 2.0% concentration or in the presence of high Na+ concentrations (>4000 mM). It was worth mentioning that 1.0% XG-SP can form a gel with a fixed shape in the presence of 5000 mM Na+. What's more, Atomic Force Microscope (AFM) images showed many cyclic configurations, branched chain ends, but no continuous linear structures in XG-SP hydrogel, also both single-stranded and double-stranded helix secondary structures were observed. In the presence of high concentration of Na+ and Ca2+, the main structure of XG-SP was multi-stranded helix, and the double-stranded helix structure might be the smallest unit. Because of the specific structure, this tailor-made XG-SP hydrogel showed better characteristics than natural xanthan, which could contribute to its application in the food industry.