Aims: The aim of the study is to evaluate the effectiveness of the preparation of nisin Z from Lactococcus lactis W8-fermented milk in controlling the growth of spoilage bacteria in pasteurized milk.
Methods and results: Spoilage bacteria isolated from pasteurized milk at 8 and 15°C were identified as Enterococcus italicus, Enterococcus mundtii, Enterococcus faecalis, Bacillus thuringiensis, Bacillus cereus, Lactobacillus paracasei, Acinetobacter sp., Pseudomonas fluorescens and Enterobacter aerogenes. These bacteria were found to have the ability to survive pasteurization temperature. Except Enterobacter aerogenes, the spoilage bacteria were sensitive to the nisin Z preparation of the L. lactis W8. Addition of the nisin Z preparation to either the skim milk or fat milk inoculated with each of the spoilage bacteria reduced the initial counts (about 5 log CFU ml⁻¹) to an undetectable level within 8-20 h. The nisin Z preparation extended the shelf life of milk to 2 months under refrigeration.
Conclusions: The nisin Z preparation from L. lactis W8-fermented milk was found to be effective as a backup preservative to counteract postpasteurization contamination in milk.
Significance and impact of the study: A rapid inhibition of spoilage bacteria in pasteurized skim and fat milk with the nisin Z preparation of L. lactis W8 is more significant in comparison with the commercially available nisin (nisin A). The nisin Z preparation can be used instead of commercial nisin, which is not effective in fat milk.
© 2011 The Authors. Letters in Applied Microbiology © 2011 The Society for Applied Microbiology.