Abstract: Nine yeast strains capable of producing exopolysaccharides as determined by the phenol/sulfuric acid method were isolated and purified from dairy fan, a traditional fermented milk product in Yunan, China by the streak plate method. These strains were identified through morphological, physiological characteristics and molecular biology techniques, including 3 strains of Rhodotorula mucilaginosa, 1 strain of Candida albicans, 4 strains of Candida zeylanoides and 1 strain of Papiliotrema aurea. A high-yield exopolysaccharide (EPS)-producing strain, namely P. aureus DF-12, was obtained, which could synthesize EPS by using various carbon sources such as glucose, sucrose and molasses, and the highest yield of EPS of 3 510 mg/L was obtained after 168 h fermentation at 28 ℃ using sucrose as carbon source. In vitro antioxidant tests indicated that the EPS from DF-12 had strong scavenging ability against 1,1-diphenyl-2-picrylhydrazyl (DPPH) and superoxide anion radicals. The experimental results provide a basis for the development and application of EPS in the food and pharmaceutical industries.

Key words: dairy fan, yeast, isolation, screening, exopolysaccharide, antioxidant activity