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

•Enzymatic conversion of lactose into galacto-oligosaccharides with β-galactosidase.•β-Galactosidase immobilized on PVDF membrane with feed under recirculation mode.•A maximum GOS yield of 30% was observed with 50g/L initial lactose concentration.•Prediction out of 5-step, 9-parameter developed model showed excellent matching.•Immobilized state enzyme on membrane showed better stability than its native state. The work focuses on producing galacto-oligosaccharides (GOS) through an enzymatic reaction with lactose under a partial recirculation loop by utilizing membrane-immobilized β-galactosidase. Cross-linking through covalent bonding, using gluteraldehyde, was employed to immobilize enzyme on a microporous polyvinylidene fluoride membrane. GOS 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°C. A maximum GOS of 30% (dry basis) was obtained after 60h of reaction time, 50g/L ILC, 241U of enzyme (specific loading of 600U/g-membrane), and 0.5mL/min of feed flow rate at 56% lactose conversion. The GOS yield increased with increased ILC and decreased feed flow rate. The selectivity of GOS formation increased by increasing both the ILC and the feed flow rate, whereas the reverse was true for mono-saccharides. The immobilized enzyme retained ∼50% of its initial activity after 30 days of storage at 20°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.