Biochemical characterization ofa b-fructofuranosidase from Rhodotorula dairenensiswith transfructosylating activity

Abstract

An extracellular b-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 sulfatepolyacrylamide 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 1C. 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 b-fructofuranosidases, produces a varied type of prebiotic fructooligosaccharides containing b-(2 ! 1)- and b-(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.