Utilization of cheddar cheese containing nisin as an antimicrobial agent in other foods

Cheddar cheese made with nisin-producing lactococci contained between 400 and 1200 IU of nisin per gram of cheese. Cultures used were Lactococcus lactis ssp. cremoris JS102, a nisin-producing transconjugant developed in the laboratories of Dr. L.L. McKay and Lactococcus lactis ssp. lactis NCDO 1404 obtained from the National Collection of Food Bacteria, Reading, England. Pasteurized process cheese spreads with 53% and 60% moisture and 0, 301 and 387 IU nisin/g were manufactured and inoculated with 2000 spores of Clostridium sporogenes PA 3679 during manufacture. The heat process did not reduce nisin activity in the cheese spreads. The spreads were incubated at 22 degrees and 37 degrees C for 90 days. Spoilage was detected by the presence of gas and/or odor in the packages. The shelf-life of the nisin-containing cheese spreads was significantly greater than that of the control cheese spreads at the lower temperature at both moisture levels, whereas the keeping quality of the higher moisture cheeses at the higher temperature was not significantly different. Club cheese or cold pack cheese spreads with moisture levels of 44% and 60% and 0, 100 and 300 IU nisin/g were made. These cold processed cheese spreads were inoculated with 1000 cfu per g of Listeria monocytogenes V7, Staphylococcus aureus 196E and spores of C. sporogenes PA 3679. Heat shocked spores of PA 3769 at the same number were added to separate lots of the cheese spread. The cold pack cheese spreads were incubated at 23 degrees and 37 degrees C for up to 8 weeks. Samples were taken weekly and analyzed for surviving organisms. Significant reductions in numbers of the non-sporeforming test microbes were noted at both temperatures, at both moisture levels and both levels of nisin. Heat shocking the spores was needed to show reduction in numbers during the storage of the cold pack cheese spreads. The data obtained in this study suggest that the use of nisin-containing cheese as an ingredient in pasteurized process cheese or cold pack cheese spreads could be an effective method of controlling the growth of undesirable microorganisms in these processed foods.