Main Article Content
Aims: To optimize fermentation conditions for microbial production of levan polymer on a low-price productive medium. Also to purified levan from Bacillus sp. V8 strain, characterization the levan polymer by 13C NMR spectroscopy and physicochemical properties.
Study Design: Optimization of environmental factors for levan production. Polymer purification and identification.
Place and Duration of Study: Agric. Microbiology Dept., Fac. of Agriculture, Ain Shams Univ., Cairo, Egypt, between January 2012 and December 2013.
Methodology: Bacillus lentus V8 strain was used as producer of levan. This strain was grown on productive medium. Cell dry weight and levan polymer were determined in all the samples at the end of the fermentation period. Study on optimal levan production conditions such as initial pH, incubation temperatures, shaking speed, inoculum size. The parameters of growth and levan were calculated from the exponential phase. Isolation and identification of levan polymer.
Results: Effect of some environmental factors on growth and levan production by Bacillus lentus V8 strain on medium supplemented with sucrose or black strap sugar cane molasses was investigated. Results indicated that the productive medium with initial pH 6.5, 10% inoculum size, incubated at 30ºC, 150rpm shaking speed gave 51.40 or 45.34gL-1 of levan dry weight on medium supplemented with sucrose or black strap sugar cane molasses, respectively. With respect to biological activity of Bacillus lentus V8 strain on modified medium supplemented with sucrose or black strap sugar cane molasses using shake flasks as a batch culture, results reveal that the fermentation period for highest cell dry weight 2.99 or 2.89gL-1 was obtained after 48 h or 66 h, respectively. The highest levan dry weight (57.95 or 49.86gL-1) and biopolymer yield (23.18 or 36.93%) on modified medium supplemented with sucrose or black strap sugar cane molasses were achieved after 60 h, respectively. A highly positive correlation coefficient between incubation period and cell dry weight, levan dry weight, polymer dry weight yield, effective yield and Yp/x, R2 values ranged from (0.91 to 0.97) and (0.89 to 0.96) on medium supplemented with sucrose or black strap sugar cane molasses, respectively. The levan produced by tested strain was identified by 13C NMR and characterized by being white color, soluble in water and precipitated with alcohol, it contains 40.86% carbon and 0.98% ash.
Conclusion: The highest amount of levan was produced by Bacillus lentus V8 strain on productive medium supplemented with sucrose [or] black strap sugar cane molasses with pH 6.5, 10% inoculum size and incubated at 30ºC for 60h at 150rpm. Characterization the levan polymer by 13C NMR spectroscopy and physicochemical properties.