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Rheda-Wiedenbrück, Germany

Hartmann H.A.,Institute Dr. Erdmann GmbH | Wilke T.,Institute Dr. Erdmann GmbH | Erdmann R.,Institute Dr. Erdmann GmbH
International Journal of Food Microbiology | Year: 2011

Consumer demands have led to an increased interest in the use of natural antimicrobials for food protection. With the objective of developing novel products for enhancing the microbial safety of food, we have tested cell-free culture supernatants (CFS's) of eight antagonistic bacterial strains for their efficacy to inhibit Listeria monocytogenes in different food matrices. The antagonistic strains represented different members of the order Lactobacillales as well as one isolate of Staphylococcus sciuri and all showed strong inhibition of L. monocytogenes on agar plates. Cell-free supernatantss were obtained after growing the bacteria in a yeast extract-glucose broth. In six of the CFS's, different class IIa bacteriocins, namely leucocin A, leucocin B, mundticin L, pediocin PA-1, sakacin A, and sakacin X, were identified as the major anti-listerial compounds. For the other two strains, the active substances could not be ascertained conclusively. The minimal effective concentration (MEC) of the individual CFS's to achieve a 2.3 log10 reduction of L. monocytogenes was determined in culture broth, whole milk, and ground beef at 4°C. While all bacteriocin-containing CFS's were effective in broth at concentrations from 52 to 205AU/ml, significant higher concentrations were needed when applied in food. Best results were obtained using CFS's containing pediocin PA-1, that displayed only three- and ten-times higher MEC's in milk (307AU/ml) and ground meat (1024AU/g) compared to broth, respectively. A twenty-fold increase in the MEC (2048AU/ml) was observed for a mundticin L-containing fermentate, and a CFS containing leucocin A and B was inactivated more than fifty-fold (>1280AU/ml) in both food matrices. Remarkably, the sakacin A and sakacin X containing CFS's displayed very selective inactivation rates, in which sakacin A was only effective in meat (512AU/g), while sakacin X was only effective in milk (2048AU/ml). In all cases, inhibition of L. monocytogenes was only transient and surviving or resistant bacteria started growing after prolonged storage. These results highlight the importance of careful testing the effectiveness of bacteriocins in the food systems for which they are intended to be applied against the selected target and non-target bacteria. Furthermore, the outgrowth of surviving or resistant bacterial populations points out that the tested bacteriocins are not suited to assure full inhibition of L. monocytogenes in a food product, if not applied in combination with additional preservative measures. © 2011 Elsevier B.V.

From a bacteriological point of view, the use of poultry for the production of raw sausages is perilous in two different aspects: First of all, the prevalence of pathogenic bacteria on poultry is higher-than-average and second, effective steps for the elimination of these bacteria are missing. This work aims to investigate the development of enteropathogenic Campylobacter spp., Listeria monocytogenes und Salmonella enterica isolates during the production of a salami-type sausage from turkey and to identify appropriate measures to improve the microbiological safety of the product. In a series of challenge tests, we monitored a rapid inactivation of inoculated Campylobacter spp. during the fermentation process and viable cells could not be isolated from the product by cultural means. On the contrary, inactivation of L. monocytogenes and Salmonella strains through the 11 days of production was insufficient, reaching 0,9 and 1,8 logio units, respectively. With the aid of appropriate anti-listerial maturation starters, Listerial counts could be effectively reduced. Unexpected effects were observed about the antimicrobial capacity of nitrite and nitrate curing agents: Both substances retarded growth of the pathogens during the manufacturing process. In addition, sodium nitrite showed a concentration-dependend inactivation of L monocytogenes, while higher concentrations (160 ppm) led to a prolonged survival of Salmonella. Substituting sodium nitrite with the traditional curing agent potassium nitrate provoked no decrease in Listerial counts but was very effective in eradicating Salmonella bacteria. Using the example of a salami-type sausage, it was demonstrated how the microbiological safety of a product can be improved by small modifications of the recipe without a significant increase in production cost or time. The application of curing agents should be productdependend and should follow the technological, bacteriological and organoleptical needs.

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