Xanthan gum is a hydrophilic heteropolysaccharide widely used in food, medicine, cosmetic, and other fields. However, its multiple applications are limited by its xanthomonadin assuming yellow color. Genetically engineered strain Xanthomonas campestris ΔrpfBΔxanK can produced xanthan gum without xanthomonadin pigment, named as "white xanthan gum", which has extremely broad market prospects. However, the fermentation conditions for its production still need further optimization. Therefore, the study optimized the fermentation medium of X. campestris ΔrpfBΔxanK strain through single-factor experiments and orthogonal experiments to improve the gum production. Scale-up experiment was carried out using a 15 L mechanically stirred fermenter, and the final production of white xanthan gum and commercially xanthan gum were compared and verified by infrared spectroscopy. The results showed that the optimal fermentation medium conditions were as follows:corn starchsucrose (3:1) 5%, peptone 0.2%, K2HPO4 0.4%, CaCO3 0.5%, soybean 0.3%, initial pH of 8, inoculation amount of 5%, shaking speed of 220 r/min, fermentation temperature of 28 ℃ for 72 h. The yield in shake flasks could reach 33.8 g/L. After scale-up experiment using a 15 L mechanically stirred fermenter, with an initial aeration rate of 1 vvm and subsequently increasing to 2 vvm, the stirring speed was set to 250 r/min for the first 36 hours and 400 r/min for the next 36 hours. The fermentation lasted 72 hours, and the final yield was 38.4 g/L. Infrared spectroscopy analysis showed that the structure of white xanthan gum matched that of commercially xanthan gum and proved that the two gum had the same structure. The study provided a scientifically reasonable fermentation strategy for the industrial application of X. campestris ΔrpfB ΔxanK strain, and laid a foundation for the further industrial application of white xanthan gum. |