Continuous nisin production in laboratory media and whey permeate by immobilized Lactococcus lactis

Continuous production of nisin in laboratory media and whey permeate was investigated using a packed-bed bioreactor. Lactococcus lactis subsp. lactis ATCC 11454 was immobilized by natural attachment to fibre surfaces and entrapment in the void volume within spiral wound fibrous matrix. The inoculated bioreactor was fed M17 medium and effect of pH, temperature, dilution rate, and substrate concentrations on nisin production was examined. Bioreactor performance was monitored by checking cell density, lactic acid production, lactose consumption, and nisin activity. Optimal nisin activity was observed at pH 5.5, 31 °C, 0.2-0.3/h dilution rate, and 30 g/l lactose in M17. The maximum nisin titre was 2.6×104 AU/ml against a nisin sensitive strain, Lactobacillus leichmannii ATCC 4797. The bioreactor was fed whey permeate, supplemented with casein hydrolysate, and growth of L. lactis and associated nisin production were monitored. Optimal conditions for continuous nisin production in whey permeate were pH 5.5, 31 °C, 10-20 g/l casein hydrolysate, and 0.2/h dilution rate. Under these conditions, a maximum nisin titre of 5.1×104 AU/ml was observed. The bioreactor was operated continuously for 6 months without encountering any clogging, degeneration, or contamination problems. The cell density in the bioreactor was 52.0 g/l with 96.4% of the cells immobilized. This study illustrates the possibility of continuous production of high concentration of bacteriocins by lactic acid bacteria for use as food biopreservatives.