RESUMEN
Xanthan gum (XG) is a bacterial exopolysaccharide widely used in various industries due to its stability and rheological properties. Low-molecular-weight xanthan gum (LXG) exhibits enhanced properties and broader applications, but current degradation methods are limited. This study introduces an innovative coupled fermentation system for the efficient production of LXG. Endo-xanthanase from Microbacterium sp. XT11 was expressed in Pichia pastoris GS115, exhibiting optimal activity at pH 6.0 and 40 °C, with broad pH tolerance. The optimized coupled fermentation system used bean sprouts juice as nitrogen source, the inoculation quantity of X. campestris: P. pastoris was 1: 3, and the pH was controlled at 6.0. In the bioreactor, the total sugar concentration reached 12.12 g/L, the reducing sugar concentration reached 5.32 g/L, and the endo-xanthanase activity increased to 1150.26 U/L, which were 2.13, 2.3, and 3.71 times higher than those at the shake flask level, respectively. The prepared LXG had a molecular weight of 1093 Da and a monosaccharide ratio of 2.0:1.57:0.89 (glucose, mannose, and glucuronic acid). Bioactivity analysis revealed its antioxidant and prebiotic properties, promoting the growth of beneficial intestinal microbiota and metabolite production. This suggests the potential of LXG as a functional ingredient in intestinal health-focused foods and supplements.
RESUMEN
In this paper, a marine environmental sensitivity index system was constructed based on three factors: the marine biological species sensitivity, the marine ecological value sensitivity and the social and economic sensitivity. Combined with numerical simulations of 137Cs in the Beibu Gulf under the condition of a level-7 nuclear accident, a comprehensive risk assessment of marine radioactivity under the simulated accident in the Beibu Gulf was carried out. The results show that the areas at high risk and medium-to-high risk to marine radioactivity are mainly concentrated within 30 km of the Fangchenggang Nuclear Power Plant. The medium-risk areas are mainly distributed in sea areas within 30-50 km of the nuclear power plant, and the other sea areas are low-risk areas. The distribution of the risk sources and the characteristics of the regional tidal currents are the main factors affecting the magnitude and distribution of the comprehensive risk of regional marine radioactivity.