Selection and improvement of lactic acid bacteria used in meat and sausage fermentation

Criteria for the selection of lactic acid bacteria (LAB) with application in meat fermentation are: i) suitability for propagation and preparation of starter cultures; and ii) safe performance in the fermenting substrate. The selection has to take in consideration the various, specific requirements of the fermentation process. In Europe these are usually best fulfilled by strains of Lactobacillus curvatus (L curvatus) and L sake. Some strains of L curvatus exhibit the potential to form tyramine and/or phenylethylamine and should not be used. Strains of L sake are free of this potential. Suitable isolates should be competitive and suppress the growth of undesired organisms. The formation by the strains of bacteriocin (for example curvacin A) can increase their competitiveness. A final proof of the suitability of the isolate is obtained in practical tests. An improvement of LAB in starter cultures can be achieved by either combining compatible strains to increase the overall metabolic activity above that level present in one single strain or by genetic modification. We have cloned and expressed in L sake and L curvatus the genes coding for catalase (katA) and lysostaphin (lys) by use of Vectors derived from LAB plasmids. Catalase activity is a technological important property not present in L curvatus. its expression was subjected to regulation in response to oxygen as it was observed in the gene donor L sake. After removing repetitive sequences in lys, the transformed strains of L sake and L curvatus acquired the potential to kill staphylococci not only in fermenting sausages but also in mayonnaise-based salads.