Enzymatic synthesis of novel fructosyl and oligofructosyl trehaloses by Aspergillus sydowi beta-fructofuranosidase.

An intracellular beta-D-fructofuranosidase produced by Aspergillus sydowi IAM 2544 was purified by Q-Sepharose and Alkyl-Sepharose chromatographies. The molecular mass was 50 kDa by SDS-PAGE analysis. The optimum pH and temperature of sucrose hydrolyzing activity of the enzyme were 5.5 and 75 degrees C, respectively, but those of fructosyl transferase activity were 5.2 and 55 degrees C, respectively. The enzyme efficiently transferred the fructose residue of sucrose as a donor to trehalose as an acceptor. And the amount of fructosyl and oligofructosyl trehaloses produced was changed by the molar ratio of trehalose as an acceptor to sucrose as a donor used. The most efficient production of the transferred products was achieved at the reaction conditions in the range of molar ratios of 1:1 to 3:1 (trehalose:sucrose). The chemical structures of these new kinds of resulting series of fructosyl and oligofructosyl trehaloses produced were identified as O-beta-D-Fru-(2-->6)-alpha-D-Glc-(1-->1)-alpha-D-glucopyranoside, O-beta-D-Fru-(2-->6)-alpha-D-Glc-(1-->1)-alpha-D-glucopyranoside, and O-beta-D-Fru-(2-->1)-O-beta-D-Fru-(2-->1)-O-beta-D-Fru-(2-->6)-alpha-D-G lc- (1-->1)-alpha-D-glucopyranoside. These results indicate that beta-fructofuranosidase from Aspergillus sydowi specifically transferred the fructose residue of sucrose to the C6-OH position of the glucose residue of trehalose at the early stage of the reaction, following the elongation of the fructose residue by the transfructosylation of the enzyme to form oligofructosyl trehalose of a longer fructose chain.