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

Wu, Mengmeng, Qu, Jianmei, Shen, Yaqi, Dai, Xiaohui, Wei, Weiying, Shi, Zhong, Li, Guoqiang, Ma, Ting
Food hydrocolloids 2019 v.87 pp. 747-757
Xanthomonas campestris, atomic force microscopy, calcium, food industry, heat treatment, hydrocolloids, hydrogels, nonfood industry, pyruvic acid, salt tolerance, sodium, storage modulus, viscosity, xanthan gum
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.