Purification, Structural Characterization, Antioxidant and Emulsifying Capabilities of Exopolysaccharide Produced by Rhodococcus qingshengii QDR4-2

Rhodococcus bacteria possess excellent capabilities to synthesize biomolecules, and some of their metabolites have been investigated and applied. However, there is a scarcity of data on the structure and applications of exopolysaccharides (EPS) produced by Rhodococcus bacteria. In the present study, a novel EPS was extracted from the fermentation broth of Rhodococcus qingshengii QDR4-2, and the yield reached 3.85 g/L using single-factor experiment in MRS medium. Following a series of purification procedures, a single component named QEPS was obtained. The monosaccharide composition of QEPS was mannose (Man) and glucose (Glc) in a molar ratio of 81.5:18.5, and its molecular weight (MW) was 9.450 x 10(5) Da. QEPS exhibited the porous structure by scanning electron microscopy (SEM) and the straight chain structure of QEPS was observed by atomic force microscopy (AFM). Moreover, results showed that QEPS consisted of <- 2)-Manp-(1 ->, <- 3)-Manp-(1 ->, <- 2,6)-Manp-(1 ->, <- 3)-Glcp-(1 ->, Glcp-(1 ->, and Manp-(1 ->. Thermogravimetric (TG) analysis determined that the degradation temperature of QEPS was 224.74 degrees C. In addition, the emulsifying capabilities, antioxidant activities, and cytotoxicity of QEPS were investigated; the findings suggested that QEPS has potential as a bioemulsifier and antioxidant with applications in health, food, and pharmaceutical industries.