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-contro lled, mixed-strain batch cultures in a supplemented whey permeate medium wi th 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 degrees C and pH 5.5 by first inoculati ng with variant T5 and then with L. diacetylactis UL719 after 8 h incubatio n, 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 1(-1) of pure nisin Z and pediocin, respectively. In pure cultures, nisin Z and pediocin productions were higher than in mixed cultures, and ma ximum activities were obtained after 10 h incubation, with approximately 10 000 AU ml(-1) (250 mpd 1(-1) pure nisin Z) and 2500 AU ml(-1) (190 mg 1(-1 ) pure pediocin). During mixed cultures, significant pediocin degradation w as observed in the culture supernatant fluid after 16 h incubation, togethe r with a sharp drop in Ped. acidilactici UL5 cell viability. In the test co nditions, the feasibility of producing a nisin/pediocin mixture by mixed-st rain fermentation was demonstrated. The bacteriocin mixture produced in a s upplemented whey permeate medium could be used as a natural foodgrade biopr eservative with a broad activity spectrum.