title: Performance of an ultrafiltration membrane bioreactor (UF-MBR) as a processing strategy for the synthesis of galacto-oligosaccharides at high substrate concentrations.
abstract: The performance of an ultrafiltration membrane bioreactor for galacto-oligosaccharides (GOS) synthesis using high lactose concentrations (470 g/L) and β-galactosidase from Aspergillus oryzae was assessed. Tested processing variables were: transmembrane-pressure (PT), crossflow-velocity (CFV) and temperature. Results showed that processing variables had significant effect on the yield, the enzyme productivity and the flux but did not on GOS concentration and reaction conversion obtained. As expected, the use of high turbulences improved mass transfer and reduced the membrane fouling, but the use of very high crossflow-velocities caused operational instability due to vortex formation and lactose precipitation. The use of a desirability function allowed determining optimal conditions which were: PT (4.38 bar), CFV (7.35 m/s) and temperature (53.1 °C), optimizing simultaneously flux and specific enzyme productivity Under these optimal processing conditions, shear-stress and temperature did not affect the enzyme but long-term operation was limited by flux decay. In comparison to a conventional batch system, at 12.5h of processing time, the continuous GOS synthesis in the UF-MBR increased significantly the amount of processed substrate and a 2.44-fold increase in the amount of GOS produced per unit mass of catalyst was obtained with respect to a conventional batch system. Furthermore, these results can be improved by far by tuning the membranearea/reactionvolume ratio, showing that the use of an UF-MBR is an attractive alternative for the GOS synthesis at very high lactose concentrations.
authors.affiliation: School of Biochemical Engineering, Pontificia Universidad Católica de Valparaíso, Chile; School of Food Engineering, Pontificia Universidad Católica de Valparaíso, Chile. Electronic address: andres.cordova@ucv.cl.
authors.forename: Andrés
authors.initials: A
authors.lastname: Córdova
authors.affiliation: School of Food Engineering, Pontificia Universidad Católica de Valparaíso, Chile.
authors.forename: Carolina
authors.initials: C
authors.lastname: Astudillo
authors.affiliation: School of Biochemical Engineering, Pontificia Universidad Católica de Valparaíso, Chile.
authors.forename: Carlos
authors.initials: C
authors.lastname: Vera
authors.affiliation: School of Biochemical Engineering, Pontificia Universidad Católica de Valparaíso, Chile.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Guerrero
authors.affiliation: School of Biochemical Engineering, Pontificia Universidad Católica de Valparaíso, Chile.
authors.forename: Andrés
authors.initials: A
authors.lastname: Illanes
mesh_terms: D001236:Aspergillus oryzae / Q000201:enzymology; D019149:Bioreactors / Q000382:microbiology*; D005656:Fungal Proteins / Q000378:metabolism; D009844:Oligosaccharides / Q000096:biosynthesis*; D014462:Ultrafiltration / Q000295:instrumentation*; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; D009844:Oligosaccharides; D001616:beta-Galactosidase
keywords: Galacto-oligosaccharides; High concentrations; Lactose; Membrane bioreactor; Ultrafiltration; β-Galactosidase