Taxonomic status of atypicalLactobacillus saké andLactobacillus curvatus strains associated with vacuum-packaged meat spoilage

Microbial interaction in cooked cured meat products under vacuum or modified atmosphere at 4 degrees C

AIMS

To investigate the antagonistic activity of two lactic acid strains against the spoilage microflora in cooked cured meat products, vacuum or modified atmosphere packed at 4 degrees C and to determine the inhibitory capacity of their bacteriocins.

METHODS AND RESULTS

Frankfurter-type sausages and sliced cooked cured pork shoulder were inoculated with Leuconostoc mesenteroides L124 and Lactobacillus curvatus L442 or with their bacteriocins. The microbial, physico-chemical (pH, L- and D-lactate, acetate and ammonia) and colour changes were studied. Results under vacuum packaging showed that in the uninoculated samples of the pork product the spoilage microflora grew but in the inoculated ones the spoilage microorganisms (e.g. Brochothrix thermosphacta and enterococci) reduced during the storage. This observation was more pronounced in the samples with the addition of bacteriocins. In the frankfurter-type sausages the spoilage microflora did not grow in the uninoculated and inoculated samples. In the modified atmosphere enriched in CO2 the population of spoilage microflora remained at low levels in both products, indicating that CO2 has an effect on the spoilage microorganisms' growth. In the pork product the concentrations of acetate and d-lactate increased while L-lactate decreased, but in the frankfurter-type sausages increase of acetate and D-lactate was not observed.

CONCLUSIONS

Lactic acid strains had an effect on the spoilage microflora growth but did not affect, negatively, the organoleptic properties of the products. These strains may be used as biopreservative cultures or their bacteriocins could be an important contribution to microbiological quality of meat products.

SIGNIFICANCE AND IMPACT OF STUDY

Establishment of biopreservation as a method for extension of shelf life of meat products.

Identification of lactic acid bacteria from spoiled, vacuum-packaged 'gravad' rainbow trout using ribotyping

A total of 296 lactic acid bacteria (LAB) isolated from spoiled, vacuum-packaged 'gravad' rainbow trout stored at 3 and 8 degrees C were characterised and identified using a molecular approach. The isolates were initially grouped according to their HindIII restriction endonuclease profiles and further identified to species level using an rRNA gene restriction pattern (ribotype) identification database. Lactobacillus sakei, L. curvatus and Carnobacterium piscicola were the three main species detected. Only one isolate was identified as C. divergens. Most of the carnobacteria were found in the samples stored at 3 degrees C. The relative proportion of L. sakei was higher in the samples stored at 8 degrees C.

Ropy slime-producing Lactobacillus sake strains possess a strong competitive ability against a commercial biopreservative

Aseptically handled Frankfurters were treated with a commercial Lactobacillus alimentarius biopreservative and inoculated with different cell concentrations of four ropy slime-producing Lactobacillus sake strains. The packages were vacuum sealed and kept at 6 degrees C for 28 days, after which the production of ropy slime was evaluated. The inoculation test was controlled by sealing the different control packages containing either aseptically manufactured sausages without any bacterial inoculation, packages containing biopreservative only or packages inoculated only with the four different ropy slime-producing strains. Authenticity of the biopreservative strain after the cold storage period was ascertained by performing EcoRI restriction endonuclease analysis of 30 randomly selected isolates originating from the biopreservative control packages. All patterns were identical to the pattern of the original L. alimentarius biopreservative strain. The biopreservative was found to be ineffective against the four ropy slime-producing L. sake strains. The strongest slime producers inoculated with approximately 1 colony forming units (CFU)/cm2 could compete efficiently with the L. alimentarius inoculated at a level of 10(7) CFU/cm2 on sausage surfaces. This commercial biopreservative failed to occupy the vital niche of the four ropy slime-producing L. sake strains leading to spoilage in almost all packages.

Bacterial spoilage of meat and cured meat products

The influence of environmental factors (product composition and storage conditions) on the selection, growth rate and metabolic activity of the bacterial flora is presented for meat (pork and beef) and cooked, cured meat products. The predominant bacteria associated with spoilage of refrigerated beef and pork, are Brochothrix thermosphacta, Carnobacterium spp., Enterobacteriaceae, Lactobacillus spp., Leuconostoc spp., Pseudomonas spp. and Shewanella putrefaciens. The main defects in meat are off-odours and off-flavours, but discolouration and gas production also occur. Bacteria associated with the spoilage of refrigerated meat products, causing defects such as sour off-flavours, discolouration, gas production, slime production and decrease in pH, consist of B. thermosphacta, Carnobacterium spp. Luctobacillus spp. Leuconostoc spp. and Weissella spp. Analysis of spoilage as measured by bacterial and chemical indicators is discussed. It is concluded that a multivariate approach based on spectra of chemical compounds, may be helpful in order to analyse spoilage, at least for spoilage caused by lactic acid bacteria. The consequences of bacteria bacteria interactions should be evaluated more.