Potential production and preservation of dahi by Lactococcus lactis W8, a nisin-producing strain

Lactococcus lactis W8 produced nisin concomitantly while fermenting milk to “dahi”, a traditional Indian fermented milk. The activity of nisin was detected at 3 h of fermentation, which increased in parallel to growth of the organism and reached its maximum at 6 h. The activity remained essentially stable thereafter. At 7 h of fermentation of milk with the strain L. lactis W8 the pH of the medium dropped to 4.2, when the milk became converted to dahi. The produced dahi displayed antibacterial property against spoilage and pathogenic bacteria including Listeria monocytogenes. When L. monocytogenes was mixed with dahi at 5.2 log CFU/ml and stored at 4 °C, the number of L. monocytogenes gradually decreased and became undetectable at 10 h. L. lactis W8 appeared to be a suitable starter culture for production of dahi from milk and preservation of the dahi.