Biochemical characterization of a β‐fructofuranosidase from Rhodotorula dairenensis with transfructosylating activity

An extracellular β-fructofuranosidase from the yeast Rhodotorula dairenensis was characterized biochemically. The enzyme molecular mass was estimated to be 680 kDa by analytical gel filtration and 172 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, of which the N -linked carbohydrate accounts for 16% of the total mass. It displays optimum activity at pH 5 and 55–60 °C. The enzyme shows broad substrate specificity, hydrolyzing sucrose, 1-kestose, nystose, leucrose, raffinose and inulin. Although the main reaction catalyzed by this enzyme is sucrose hydrolysis, it also exhibits transfructosylating activity that, unlike other microbial β-fructofuranosidases, produces a varied type of prebiotic fructooligosaccharides containing β-(2→1)- and β-(2→6)-linked fructose oligomers. The maximum concentration of fructooligosaccharides was reached at 75% sucrose conversion and it was 87.9 g L−1. The 17.0% (w/w) referred to the total amount of sugars in the reaction mixture. At this point, the amounts of 6-kestose, neokestose, 1-kestose and tetrasaccharides were 68.9, 10.6, 2.6 and 12.7 g L−1, respectively.