Production of Fructooligosaccharides Using a Commercial Heterologously Expressed <i>Aspergillus</i> sp. Fructosyltransferase

Abstract

The catalytic properties of Seqenzym® FT, a fungal fructosyltransferase heterologously expressed in yeasts, were investigated at a temperature of 55 °C and pH 5.5. The initial rate measurements showed that the transfructosylation rate was only slightly inhibited by sucrose above the concentration of 1.5 M. A rather low level of hydrolytic side activity was observed even at sucrose concentrations as low as 0.25 M. In progress curve experiments, the mass yield of fructooligosaccharides (FOS) reached a maximum value of 57% at this sucrose concentration, although it dropped to about 35% later on. At high initial sucrose concentrations up to 2 M, the FOS yield reached a maximum value of approximately 63% at a sucrose conversion of approximately 90%. Although neither the yield nor the conversion changed much later on, the progress of the reaction was manifested by the gradual depletion of shorter chain FOS, 1-kestose and nystose, and the accumulation of 1-β-fructofuranosyl nystose. At initial sucrose concentrations of 2 M, the degree of polymerization expressed through the number of fructosyl units grew from 2.3 at a conversion degree of 87% to 3.1 at a conversion degree of 94%. Compared to other commercial preparations, Seqenzym® FT can better produce FOS with a higher degree of polymerization.

Keywords

• fructooligosaccharides
• fructosyl transferase
• heterologous expression
• <i>Aspergillus</i> sp.
• degree of polymerization