Levan versus fructooligosaccharide synthesis using the levansucrase from Zymomonas mobilis: effect of reaction conditions

This work addresses the effect of sucrose concentration and temperature on the three activities displayed by the levansucrase from Zymomonas mobilis: formation of levan (polymerization), production of short-chain fructooligosaccharides (FOS), and sucrose hydrolysis. Of the conditions tested, levan formation reached the highest value at 4ºC and 100 g/L sucrose. The increase of temperature (40ºC) and sucrose concentration (600 g/L) caused a significant decrease of the levan concentration and a higher production of FOS. However, an increase of the temperature also caused an enhancement of the undesired hydrolytic activity. Several inulin-type FOS (1-kestose, nystose, 1F-fructosylnystose), neoFOS (blastose, neokestose, neonystose) and levan-type FOS (6-kestose, 6,6-nystose) were synthesized by levansucrase. The latter compound was purified and characterized by mass spectrometry and 2D NMR. Using 600 g/L sucrose at 40°C, the maximum yield of FOS was reached at 85% sucrose conversion; at this point, the reaction mixture contained (in weight basis) 31% glucose, 14% fructose, 15% sucrose and 40% FOS (including a small contribution of levan).This work was supported by a grant from the Spanish Ministry of Economy and Competitiveness (BIO2013-48779-C4-1-R). We thank the support of COST-Action CM1303 on Systems Biocatalysts. We thank Amano Enzyme Inc. (Japan) for the kind donation of the levansucrase. We thank Beneo Iberica for the generous supply of an inulin sample (Raftiline). P. S-M. thanks the Spanish Ministry of Education for FPU Grant.Peer reviewe