Production and partial characterization of fructose-rich exopolysaccharide from a newly isolated halophilic strain Vreelandella sp. DT-Z4.

Exopolysaccharide (EPS) synthesis of halophilic microorganisms is often reported as an adaptation to high-salt environments, and the unique structural and functional characteristics of these EPSs make them valuable biomaterials with promising application potential. A moderately halophilic strain, Vreelandella sp. DT-Z4, was isolated from Qinghai saline soil, and its EPS yield reached 3.09 g/L after fermentation optimization. The polysaccharide fraction (designated EPS-Z4) was partially purified using ethanol precipitation, deproteinization, and dialysis processes, and subsequently characterized for monosaccharide composition, spectroscopic features, and morphological properties. Analytical results revealed that EPS-Z4 was a fructose-rich polysaccharide composed of 97.6% fructose, 1.4% glucose, and 0.5% uronic acid. Functional group analysis confirmed the presence of absorption peaks characteristic of polysaccharides. The polysaccharide showed a degradation temperature (Td = 275.9 °C), water solubility (85.8%), and oil-holding capacity (321%). Morphological observations revealed a dense, layered network structure. Based on these physicochemical properties, the fructose-rich polysaccharide fraction EPS-Z4 may merit further investigation as a stabilizer in high-temperature food processing or as a biological agent for the remediation of saline-alkali soils.