Characteristics of Levansucrase and Its Application for the Preparation of Levan and Levan-Type Oligosaccharides

Both inulin and levan are two types of β-fructan, wherein inulin is well-known as β-(2, 1) fructan that has been discussed in the previous chapter. Levan is another β-type fructan that possesses a non-reductive sucrose at its end and applies β-(2, 6) linkage as its skeleton. Similar to inulin, levan also existed naturally in some plants, but the amount is low and difficult to be largely obtained by extraction. Nevertheless, it has shown that the levansucrase-harboring microorganism could produce levan as their main product from the sole substrate sucrose. Although the reaction is simple, the catalytic efficiency, molecular weight, chain distribution, and physiochemical property of final product varied substantially among different levansucrases (LSase, EC 2.4.1.10). In short, some enzymes were found to mainly generate long-chain and high molecular weight levan, whereas some produced a wide variety of short-chain levan-type oligosaccharides. Moreover, the molecular weight of levan has a great impact on its practical application. In this chapter, the property of levan and its biological production by microbial LSase as well as different their application would be discussed.