Synthesis of galacto-oligosaccharides from lactose using immobilized cells of Kluyveromyces marxianus NCIM 3551

• Sodium alginate immobilized cell system for continuous synthesis of GOS in packed bed reactor.
• A productivity of 21.3 g/L/h with immobilized cells with reusability up to 10 cycles.
• High yield of 64.0 g/L GOS at low substrate concentration of 20% (w/v).

Sodium alginate immobilized cells of Kluyveromyces marxianus NCIM 3551 cells were used for synthesis of galacto-oligosaccharides (GOS) using lactose as a substrate through transgalactosylation approach. The immobilized cells retained 84.4% of the original β-galactosidase activity displayed by free cells. An increase in thermo-stability and a slight shift in pH optimum was observed for β-galactosidase in immobilized cells. Maximum GOS concentration of 72.0 g/L and specific GOS productivity 60.0 g/L/U was obtained using free cells as opposed to 42.6 g/L and productivity of 35.6 g/L/U for immobilized cells. A repeated batch reaction was carried out using free and immobilized cells for 10 cycles, of 3 h each, using 20% lactose (w/v) with a nearly similar productivity of 24.0 g/L/h and 21.3 g/L/h respectively. Based on the stability of the immobilized cells, continuous synthesis of GOS was carried out for 10 days in packed bed bioreactor using immobilized cells at a loading of 28.8 units/reactor volume. A yield of 64.0 g/L of GOS and a productivity of 21.3 g/L/h was achieved at an optimized flow rate of 1.0 mL/min. The system here demonstrated the feasibility of using whole cells for production of GOS in a packed bed reactor.

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