Dried alginate-entrapped enzymes (DALGEEs) and their application to the production of fructooligosaccharides

► A simple modification of the calcium alginate enzyme entrapment technique is proposed. ► The obtained biocatalysts (DALGEEs) do not re-swell in concentrated sucrose solutions. ► DALGEEs show high volumetric activity and microbial resistance. ► Volumetric productivity of DALGEEs in fixed-bed bioreactors was improved. ► Operational stability of DALGEEs was impressive, with no loss of activity during 700h. A modification of the classical calcium alginate enzyme entrapment technique is described aiming to overcome some of the limitations of the former gel-based biocatalysts. Dried alginate entrapped enzymes (DALGEEs) were obtained dehydrating calcium alginate gel beads containing entrapped enzymes. A fructosyltransferase from Aspergillus aculeatus, present in Pectinex Ultra SP-L, was entrapped using this technique. The resulting DALGEEs were successfully tested both operating batchwise and in a continuous fixed-bed reactor for fructooligosaccharides (FOS) synthesis from sucrose. Interestingly, DALGEEs did not re-swell upon incubation in concentrated (600g/L) sucrose solutions, probably due to the lowered water activity (aw) of such media. Confocal laser scanning microscopy of DALGEEs revealed that the enzyme molecules accumulated preferably in the shell of the particles. DALGEEs showed an approximately 30-fold higher volumetric activity (300U/mL) compared with the calcium alginate gel beads. Moreover, a significant enhancement (40-fold) of the space-time-yield of fixed-bed bioreactors was observed when using DALGEEs as biocatalyst compared with gel beads (4030g/dayL of FOS vs. 103g/dayL). The operational stability of fixed-bed reactors packed with DALGEEs was extraordinary, providing a nearly constant FOS composition of the outlet during at least 700h. It was also noticeable their resistance against microbial attack, even after long periods of storage at room temperature. The DALGEEs immobilisation strategy may also be useful for other biotransformations, in particular when they take place in low aw media.