Enzyme, β-galactosidase immobilized on membrane surface for galacto-oligosaccharides formation from lactose: Kinetic study with feed flow under recirculation loop

The work focuses on producing galacto-oligosaccharides (GUS) through an enzymatic reaction with lactose under a partial recirculation loop by utilizing membrane-immobilized beta-galactosidase. Cross-linking through covalent bonding, using gluteraldehyde, was employed to immobilize enzyme on a microporous polyvinylidene fluoride membrane. GUS synthesis was carried out in a laboratory fabricated reaction cell, whereby three immobilized membranes were housed in series. The reaction was conducted at varying initial lactose concentrations (ILCs) and feed flow rates at pH 6 and 40 degrees C. A maximum GUS of 30% (dry basis) was obtained after 60 h of reaction time, 50 g/L ILC, 241 U of enzyme (specific loading of 600 U/g-membrane), and 0.5 mL/min of feed flow rate at 56% lactose conversion. The GUS yield increased with increased ILC and decreased feed flow rate. The selectivity of GUS formation increased by increasing both the ILC and the feed flow rate, whereas the reverse was true for mono-saccharides. The immobilized enzyme retained similar to 50% of its initial activity after 30 days of storage at 20 degrees C, while the native enzyme lost 100% of its activity within 21 days. Furthermore, a five-step, nine-parameter model was developed, and simulated results showed excellent agreement with the experimental data. (C) 2014 Elsevier B.V. All rights reserved.