Fructo-oligosaccharides: Enzymic synthesis from sucrose

Fructo-oligosaccharides are naturally occurring molecules present in numerous edible plants. They are short chain oligosaccharides composed of 1 to 3 fructosyl units linked in b -1-2 on a sucrose molecule. In ascending order of polymerization degree, they are kestose or GF2, nystose or GF3 and fructosylnystose or GF4. These molecules are synthesized from sucrose by a fructosyl transferase produced by Aspergillus niger. The synthesis reaction involves a group transfer without cofactor intervention. During this reaction, sucrose acts as fructosyl donor as well as acceptor. We have studied the kinetic of the synthesis reaction in batch. During the time course of the reaction, the medium contains unreacted sucrose, glucose from the sucrose used as fructosyl donor and synthesis products: GF2, GF3, GF4. We can notice also the presence of fructose in very small concentration. This fructose is produced in a hydrolysis side reaction catalysed by the same enzyme. The influence of each sugar has been studied independently in initial velocity conditions. This approach pointed out several inhibitions. Every initial velocity equation can be described as the ratio of polynomial functions of substrate concentration. The form of the function used is as follows:

Using the kinetic parameters obtained for each initial velocity equation, it was possible to work out a global model. The evolution of the sugar concentrations during the time course of a total reaction can be correctly described by our model.