Process intensification by immobilization of β-galactosidase on a mixed matrix membrane: galacto-oligosaccharides production as a case study

Datum: 21 november 2013

Locatie: University of Antwerp, Campus Middelheim, A.143 - Middelheimlaan 1 - 2020 Antwerp

Tijdstip: 16 uur

Organisatie / co-organisatie: Department of Bio-Engineering Sciences

Promovendus: Peter Jochems

Promotor: Prof. dr. Ludo Diels

Co-promotor: Winnie Dejonghe

Korte beschrijving: PhD defence Peter Jochems - Faculty of Sciences

Abstract: This PhD focused on the development of a biocatalytic membrane reactor for the production of galacto-oligosaccharides (GOS) using in-house developed mixed matrix membranes (MMMs). A biocatalytic membrane is a matrix for enzyme immobilization as well as a selective barrier. The enzyme here studied, β-galactosidase, is used industrially for the production of GOS. Immobilization of β-galactosidase on MMMs was performed by adsorption in a first phase. This adsorption is possible because MMMs were made from polysulphone and zirconia, which is well known to adsorb proteins. The β-galactosidase adsorbed on the MMMs turned out to be unstable during process conditions. Phosphates in the reaction mixture caused fast desorption of the enzymes.

Because the membranes contain zirconia, it is theoretically possible to functionalize this zirconia with conventional ceramic functionalization techniques. However, it was not certain that the membrane could withstand these types of functionalization. Silanization and grafting with phosphonic acids were two chemistries that were tested on the MMMs. Membrane characteristics did not deteriorate after membrane functionalization and enzyme immobilization.

In a next phase, a free enzyme system was compared with enzyme membrane reactors (EMRs), a packed bed reactor (PBR) and biocatalytic membrane reactors (BMRs) for GOS production, yield and stability. The free enzyme system achieved the highest GOS concentration (26.7%). The EMRs in which the enzyme is retained in the vessel through an ultrafiltration membrane, were tested in continuous mode for a relatively short period of time, but were found to be stable for 12 h, achieving GOS concentrations around 19-20%. The PBR contained zirconia powder with covalently linked β-galactosidase and maintained stable production of GOS for 11 days. The dilution rate of this reactor was set too high and this resulted in GOS concentrations of only 15.7%. However, this indicates the stability of the immobilized enzymes. The BMRs with β-galactosidase covalently immobilized on/in MMMs were tested for 4-8 days, and achieved GOS concentrations of 10-17%. Also these reactors were stable, however, all long term experiments were hampered by the presence of proteins in the lactose solutions. This problem needs to be solved to truly assess the potential of the different reactors.

Process intensification by immobilization of β-galactosidase on a mixed matrix membrane: galacto-oligosaccharides production as a case study