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Aims:To optimize the practical use of the bacteriocin producing Leuconostoc carnosum 4010 in order to inhibit the growth of Listeria monocytogenes in sliced meat products. Methods and Results: Four different methods for biopreservation using the partially purified bacteriocin or the living culture of Leuc. carnosum 4010 were evaluated. The methods using the living protective culture added to the sliced gas packed meat product were more effective in preventing growth of L. monocytogenes than the use of the partially purified leucocins 4010 or bacteriocin produced during fermentation before heat treatment of the saveloy. The application method giving the highest reduction in L. monocytogenes used nozzles for sprinkling the protective culture on all surfaces of each slice of the meat product. In the control samples without the protective culture, L. monocytogenes grew to ca. 10 7 CFU g )1 , whereas for the application method using nozzles for distributing the protective culture, counts of L. monocytogenes never exceeded 10 CFU g )1 during 4 weeks of storage at 10°C. Conclusions: The live cells of the bacteriocin producing Leuc. carnosum 4010 was the most efficient method as it inhibited the growth of L. monocytogenes in cooked, sliced and gas packed saveloy stored at 5 and 10°C for 4 weeks. Significance and Impact of the Study: The results indicate that biopreservation with lactic acid bacteria is a suitable alternative to chemical preservatives. An even distribution of the protective culture was found to be essential for the efficacy of the protective culture in pilot plant trials.

The decontamination of a rotating cutting tool used for slicing in the meat industry by means of atmospheric pressure plasmas is investigated. The target is Listeria monocytogenes, a bacterium which causes listeriosis and can be found in plants and food. The non-pathogenic species, Listeria innocua, is used for the experiments. A rotating knife was inoculated with Listeria innocua. The surface of the rotating knife was partly exposed to an atmospheric pressure dielectric barrier discharge operated in air, where the knife itself served as a ground electrode. The rotation of the knife ensures a treatment of the whole cutting tool. A log 5 reduction of Listeria innocua is obtained after 340 s of plasma operation. The temperature of the knife after treatment was found to be below 30°C. The design of the setup allows a decontamination during slicing operation.

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The effects of acidified-nitrite stress on the growth initiation and intracellular pH (pH i ) of individual cells of Debaryomyces hansenii and Candida zeylanoides were investigated. Our results show that 200 g/ml of nitrite caused pronounced growth inhibition and intracellular acidification of D. hansenii at an external pH (pH ex ) value of 4.5 but did not at pH ex 5.5. These results indicate that nitrous acid as such plays an important role in the antifungal effect of acidified nitrite. Furthermore, both yeast species experienced severe growth inhibition and a pH i decrease at pH ex 4.5, suggesting that at least some of the antifungal effects of acidified nitrite may be due to intracellular acidification. For C. zeylanoides, this phenomenon could be explained in part by the uncoupling effect of energy generation from growth. Debaryomyces hansenii was more tolerant to acidified nitrite at pH ex 5.5 than C. zeylanoides, as determined by the rate of growth initiation. In combination with the fact that D. hansenii was able to maintain pH i homeostasis at pH ex 5.5 but C. zeylanoides was not, our results suggest that the ability to maintain pH i homeostasis plays a role in the acidified-nitrite tolerance of D. hansenii and C. zeylanoides. Possible mechanisms underlying the different abilities of the two yeast species to maintain their pH i homeostasis during acidified-nitrite stress, comprising the intracellular buffer capacity and the plasma membrane ATPase activity, were investigated, but none of these mechanisms could explain the difference.

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