Production of a nisin Z/pediocin mixture by pH‐controlled mixed‐strain batch cultures in supplemented whey permeate

The conditions for high production of nisin Z and pediocin during pH‐controlled, mixed‐strain batch cultures in a supplemented whey permeate medium with Lactococcus lactis subsp. lactis biovar. diacetylactis UL719, a nisin Z producer strain, and variant T5 of Pediococcus acidilactici UL5, a pediocin‐producing strain resistant to high concentrations of nisin, were studied. Mixed cultures were performed at 37 °C and pH 5·5 by first inoculating with variant T5 and then with L. diacetylactis UL719 after 8 h incubation, and were compared with single‐strain batch cultures. High productions of both nisin Z and pediocin were obtained after 18 or 16 h incubation during mixed cultures, with titres of 3000 and 730 AU ml −1 , or 1060 and 1360 AU ml −1 , respectively, corresponding to approximately 75 and 55, or 25 and 100 mg l −1 of pure nisin Z and pediocin, respectively. In pure cultures, nisin Z and pediocin productions were higher than in mixed cultures, and maximum activities were obtained after 10 h incubation, with approximately 10 000 AU ml −1 (250 mg l −1 pure nisin Z) and 2500 AU ml −1 (190 mg l −1 pure pediocin). During mixed cultures, significant pediocin degradation was observed in the culture supernatant fluid after 16 h incubation, together with a sharp drop in Ped. acidilactici UL5 cell viability. In the test conditions, the feasibility of producing a nisin/pediocin mixture by mixed‐strain fermentation was demonstrated. The bacteriocin mixture produced in a supplemented whey permeate medium could be used as a natural food‐grade biopreservative with a broad activity spectrum.