Structure and characterization of an extracellular polysaccharide from Paenibacillus polymyxa 88A

Levan-type polysaccharides, produced by various organisms, are nontoxic, biocompatible, and biodegradable polymers with a wide range of biological activities. They have high potential for use in medicine, cosmetology, and industry. A large amount of levan (41.1 g L^-1) was recovered by ethanol precipitation from a liquid nutrient medium of Paenibacillus polymyxa 88A that contained 15 % w/v sucrose as a carbon source. The levan was fractionated by gel-permeation and anion-exchange chromatography and was analyzed by DRIFT and NMR spectroscopy. It was found that levan was represented by slightly branched chains composed of β-(2→6)-Fruf residues. The average molecular mass of the levan was about 1.9 MDa. When shear stress was applied at different temperatures, aqueous levan solutions showed pseudoplastic behavior. As found by SEM, a freeze-dried powdered levan sample had a microporous structure. The levan had excellent emulsifying activity toward sunflower oil, forming an emulsion with long-term stability. Analysis of the antioxidant activity of the levan showed a higher, dose-dependent activity toward ABTS, as compared with that toward DPPH. Finally, the bioactivity of the levan was examined by MTT assay by using human cervical carcinoma (HeLa) cells.