Production of fructo-oligosaccharide syrup through catalysis of Bacillus amyloliquefaciens levanase and immobilized Ba-SacB on cell lysate

Levan is a type of fructan with β-(2, 6) fructosyl linkage. In recent years, levan has been used in the medicinal, food and chemical industries for its excellent physicochemical properties of good thermal stability, low viscosity, pseudoplasticity, and non-swelling in water. The levansucrase is key enzyme responsible for biosynthesis of levan from substrate sucrose. In the present study cell lysate of Escherichia coli was used as support for convenient immobilization of Ba-SacB (i.e., Ba-SacB-Cell-Lysate) under the action of dopamine. Compared with the free Ba-SacB, the Ba-SacB-Cell-Lysate showed surprisingly enhanced pH stability in the pH range 6–9, and improved relative activities in the pH ranges 4–5 and 7–10. With the presence of 10% (v/v) butyl alcohol, 5mmol/L Fe³⁺, and after vortex for 90 min, the Ba-SacB-Cell-Lysate showed up to 14.32 times, 4.63 times, and 9.2 times higher relative activities than the free Ba-SacB. The Ba-SacB-Cell-Lysate kept nearly 81% of the residual activity after 9 cycles of reuse. The fructo-oligosaccharide syrup (FOS) was efficiently produced through the catalysis of levanase with the substrate of levan produced by Ba-SacB-Cell-Lysate, and the preparation conditions were optimized by Box-Behnken response surface methodology.