Production and characterization of a bioflocculant produced by Aspergillus flavus

► Cation-independent bioflocculant produced by Aspergillus flavus. ► Sucrose and peptone are the most favorable sources for bioflocculant production. ► The bioflocculant mainly consists of polysaccharide and protein with a molecular weight of 2.57×104Da. ► The bioflocculant is stable at wide ranges of pH and temperature. The production and characterization of a bioflocculant, IH-7, by Aspergillus flavus was investigated. About 0.4g of purified bioflocculant with an average molecular weight of 2.574×104Da could be obtained from 1L of fermentation medium. The bioflocculant mainly consisted of protein (28.5%) and sugar (69.7%), including 40% of neutral sugar, 2.48% of uronic acid and 1.8% amino sugar. The neutral sugar components are sucrose, lactose, glucose, xylose, galactose, mannose and fructose at a molar ratio of 2.4:4.4:4.1:5.8:9.9:0.8:3.1. Fourier-transform infrared spectroscopy analysis revealed that purified IH-7 contained hydroxyl, amide, carboxyl and methoxyl groups. The elemental analysis of purified IH-7 showed that the weight fractions of the elements C, H, O, N and S were 29.9%, 4.8%, 34.7%, 3.3%, and 2.0%, respectively. IH-7 had good flocculating rate in kaolin suspension without cation addition and stable over wide range of pH and temperature.