Isolation, screening and characterization of bacteriocin-producing lactic acid bacteria isolated from traditional fermented food

100 lactic acid bacterial strains isolated from traditional fermented foods (yoghurt, milk cream, sour dough and milk) were screened for bacteriocin p roduction. Twenty six strains producing a nisin-like bacteriocin were selec ted. Most of these isolates gave only a narrow inhibitory spectrum, althoug h one showed a broad inhibitory spectrum against the indicator strains test ed, this strain was determined as Lactococcus lactis. The influence of several parameters on the fermentative production of nisin by Lactococcus lactis was studied. Production of nisin was optimal at 30 d egrees C and in the pH range 5.5-6.3. The effect of different sulphur and n itrogen sources on Lactococcus lactis growth and nisin production was studi ed. Magnesium sulfate and manganese sulfate were found to be the best sulph ur sources while triammonium citrate was the best inorganic nitrogen source and meat extract, peptone and yeast extract were the best organic nitrogen source for nisin production.