Galacto-oligosaccharide synthesis using chemically modified β-galactosidase from Aspergillus oryzae immobilised onto macroporous amino resin

The goal of this study was to establish an efficient immobilisation protocol for β-galactosidase from Aspergillus oryzae onto the polystyrenic macroporous resin Purolite® A-109 for better utilisation of its transglactosylation activity and application in galacto-oligosaccharide (GOS) synthesis. This was achieved by improving simple ionic adsorption by carboxyl group activation on the enzyme surface with carbodiimide, enabling covalent immobilisation. This yielded significantly increased operational stability, assayed as GOS synthesis, in a batch reactor, and even more prominently, in a fluidised bed reactor (73% activity retained after 10 cycles). The immobilised enzyme showed two very beneficial advantages over the free enzyme for future applications: higher affinity towards catalysing transgalactosylation than towards hydrolysis and shift of pH optimum towards more acidic conditions. GOS synthesis performed under the optimum conditions obtained (400 g L−1 lactose, pH 4.5, 50 °C) yielded 87 g L−1 and 100 g L−1 for batch and fluidised bed reactors, respectively.