Study of the Ecology of Fresh Sausages and Characterization of Populations of Lactic Acid Bacteria by Molecular Methods

Abstract

In this study, a polyphasic approach was used to study the ecology of fresh sausages and to characterize populations of lactic acid bacteria (LAB). The microbial profile of fresh sausages was monitored from the production day to the 10th day of storage at 4°C. Samples were collected on days 0, 3, 6, and 10, and culture-dependent and -independent methods of detection and identification were applied. Traditional plating and isolation of LAB strains, which were subsequently identified by molecular methods, and the application of PCR-denaturing gradient gel electrophoresis (DGGE) to DNA and RNA extracted directly from the fresh sausage samples allowed the study in detail of the changes in the bacterial and yeast populations during storage. Brochothrix thermosphacta and Lactobacillus sakei were the main populations present. In particular, B. thermosphacta was present throughout the process, as determined by both DNA and RNA analysis. Other bacterial species, mainly Staphylococcus xylosus, Leuconostoc mesenteroides, and L. curvatus, were detected by DGGE. Moreover, an uncultured bacterium and an uncultured Staphylococcus sp. were present, too. LAB strains isolated at day 0 were identified as Lactococcus lactis subsp. lactis, L. casei, and Enterococcus casseliflavus, and on day 3 a strain of Leuconostoc mesenteroides was identified. The remaining strains isolated belonged to L. sakei. Concerning the yeast ecology, only Debaryomyces hansenii was established in the fresh sausages. Capronia mansonii was initially present, but it was not detected after the first 3 days. At last, L. sakei isolates were characterized by randomly amplified polymorphic DNA PCR and repetitive DNA element PCR. The results obtained underlined how different populations took over at different steps of the process. This is believed to be the result of the selection of the particular population, possibly due to the low storage temperature employed.Fresh sausages are products made of pork, beef, or mixed meats, with the addition of salt, different aromas and spices, white wine, pepper, and garlic, depending on local preparation. The traditional Italian fresh sausage is produced only with the use of pork meat, pork fat, aromas, and salt. The meat and the fat are ground together in pieces that can have different dimensions based on the type of sausage to be produced. The different ingredients after mixing are used to fill natural casings from pigs or goats. The fresh sausages can be packaged in normal or modified atmosphere and stored at 4°C for a maximum period of 10 days.Fresh sausages are highly perishable products with a pH value not lower than 5.5 and water activity (A w ) equal to or higher than 0.97. Since no fermentation process is taking place during the storage at 4°C, the hygienic quality of the raw materials is the main factor affecting the final value of the product.The microbiological profile of the product is characterized by the presence of aerobes, facultative anaerobes, psychrotrophs, mesophiles, which are responsible for spoilage, and...

Microbial Community Structure and Dynamics of Dark Fire-Cured Tobacco Fermentation

“…Noteworthy is the specificity of the association between D. hansenii and several lactic acid and coryneform bacteria, including those we isolated from fermenting tobacco. These microbial consortia are typical of certain fermenting substrates that are characterized by a low C/N ratio, such as ripening cheeses (2,4,10,31,36,43,61), fresh sausages (7,47), vegetables (35), and algae (57). An association between D. hansenii and P. pentosaceus, revealed for tobacco samples (Tables 4 and 5), has previously been described for sorghum fermentation (35), and the same yeast has been isolated from the surface microflora of many brick cheeses in association with several coryneform bacteria, including C. ammoniagenes (58).…”

Analyses of Dynamics in Dairy Products and Identification of Lactic Acid Bacteria Population by Molecular Methods

“…V3 region of the bacterial 16S rRNA gene and the D1 region of eukaryotic 26s rRNA gene taken from the microbial population in the milk of cheese and in the traditional blue veined Spanish cheese made by using rennet extract were analyzed and aimed to be identified. El-Baradei et al (2007) Cocolin et al (2004) identified Clostridium spp in Late Blowing cheese samples by using PCR-DGGE method. They determined Clostridium spp.…”

Lactic Acid Bacteria as Starter-Cultures for Cheese Processing: Past, Present and Future Developments

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