rRNA gene restriction patterns as a characterization tool for Lactobacillus sake strains producing ropy slime

http://www.elsevier.nl/locate/01681605The rRNA gene restriction patterns (ribotypes) of 69 ropy slime producing Lactobacillus sake strains isolated mainly from vacuum-packaged meat products of ten meat plants were determined. Ribotypes of these spoilage bacteria were compared to the corresponding pat-terns of non-ropy L. sake strains, and also to other species of the genus Lactobacillus, Carnobacterium and Weissella associated with meat products. Ribotyping divided the ropy slime-producing L. sake strains into four characteristic groups corresponding to the phenotypic carbohydrate grouping. The major group was contaminating nine plants located in different parts of Finland and no association between certain ribotypes and individual plants was detected. Dif-ferences between ribotypes of slime producing and non-ropy strains of L. sake group sharing the same carbohydrate pattern were not found. Otherwise ribotyping distinguished the ropy slime producing strains from the non-ropy L. sake reference strains. All L. sake strains were distinguished from other species of the genus Lactobacillus, Carnobacterium and Weissella by characteristic band-ing patterns obtained especially with Hind III digestion. These results suggest that ribotyping is a suitable method for detection and surveillance of the contamination of ropy slime producing L. sake strains but the patterns alone cannot be used as markers of slime production capability. Comparison of ribotypes between differ-ent species of the genus Lactobacillus suggest that ribotyping may also be a suitable method for species identification within the genus Lactobacillus

The spoilage flora of vacuum-packaged, sodium nitrite or potassium nitrate treated, cold-smoked rainbow trout stored at 4°C or 8°C

http://www.elsevier.nl/locate/01681605The spoilage flora of vacuum-packaged, salted, cold-smoked rainbow trout fillets, with or without the addition of nitrate or nitrite, stored at 4°C and 8°C, was studied. Of 620 isolates, lactic acid bacteria were the major fraction (76%), predominating in all samples of spoiled product. However, the phenotypical tests used were insufficient to identify the lactic acid bacteria to the species level. Gram-positive, catalase-positive cocci, Gram-negative, oxidase-negative rods and Gram-negative, oxidase-positive rods were found in 6%, 16% and 2% of the samples, respectively. Of 39 Gram-positive, catalase-positive cocci, 29 were identified as staphylococci and 10 as micrococci. Eighty-five isolates were found to belong to the family Enterobacteriaceae, with 45 of those being Serratia plymuthica. Eleven isolates from the nitrate treated samples stored at 8°C were identified as Pseudomonas aeruginosa. The occurrence of P. aeruginosa and staphylococci in the nitrate-containing samples, stored at 8°C, may cause problems with respect to the safety of the product. The types of lactic acid and other bacteria in the spoilage flora were generally reduced by the addition of nitrate or nitrite to fillets

Microbial ecology of marinated meat products

www.elsevier.com/locate/meatsciMarinated meat products are consumed increasingly because they are convenient in meal preparing. In addition to sensory effects, marinating has been considered to increase product safety and shelf life quality. There are variations in meat marinating technologies around the world. In Finland, marinades are complex sauces which have a great effect on product appearance and taste. They are water-oil emulsions typically containing salt, sugar and acids (acetic, citric), rheology-improving additives (like xanthan gum and guar gum), antimicrobial agents (like sorbate and benzoate) spices and aroma strengtheners. The pH of these marinades is usually acidic, less than 5, so sugar is used to cut the edge of the acidic taste. Marinated meat products are usually packaged under modified atmospheres to prevent the growth of aerobic spoilage organisms. This results in the growth of psychrotrophic, anaerobic bacteria and lactic acid bacteria (LAB) are the dominating spoilage organisms in these products. Marinating did not increase the shelf life of Finnish poultry products and it strongly selects certain spoilage-associated novel LAB species. Surprisingly, it did not have a strong inhibitory effect on Campylobacter. This may be due to the buffering capability of meat quickly neutralizing the pH of the acidic marinade. The change in the acidic pH towards neutrality also results in dissociation of the lipophilic acids making their antimicrobial effect nonexistent

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

http://www.elsevier.nl/locate/01681605Aseptically handled Frankfurters were treated with a commercial Lactobacillus alimentarius biopreservate and inoculated with different cell concentrations of four ropy slime-producing Lactobacillus sake strains. The packages were vacuum sealed and kept at 6°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 biopreservate only or packages inoculated only with the four different ropy slime-producing strains. Authenticity of the biopreservate strain after the cold storage period was ascertained by performing EcoRI restriction endonuclease analysis of 30 randomly selected isolates originating from the biopreservate control packages. All patterns were identical to the pattern of the original L. alimentarius biopreservate strain. The biopreservate was found to be quite ineffective against the four ropy slime-producing L. sake strains. The strongest slime producers inoculated with approximately 1 CFU/cm2 could compete efficiently with the L. alimentarius having an onset concentration of 107 CFU/cm2 on sausage surfaces. This commercial biopreservate failed to occupy the vital niche of the four ropy slime-producing L. sake strains leading to spoilage in almost all packages

Evaluation of Lactobacillus sake contamination in vacuum-packaged sliced cooked meat products by ribotyping

Contamination of sliced cooked meat products with a Lactobacillus sake starter strain was suspected to cause spoilage in the products before the end of the expected shelf life. Slicing and vacuum packaging of the cooked products was done in the room in which the fermented product was handled. Since L. sake strains are known to be a dominant part of spoilage microflora associated with vacuum-pack-aged meat products, a contamination study was performed. One hundred and eighteen strains were isolated from 6 spoiled vacuum packaged meat products and from the surfaces of the packaging room and adjac-ent refrigerators. DNA was isolated from these strains and cleaved using Eco RI and Hind III restriction endonucleases to obtain characteristic ribotypes. Corresponding ribotypes of the L. sake starter strain were compared to the 14 different patterns obtained from the strains growing in spoiled products and on surfaces by Eco RI digestions. The L. sake starter strain was shown to contaminate the packaging room and it was also isolated from one of the products. However, it was not a dominant strain in this product and it could not be linked to the other products. Our results indicated that handling the fermented product in the refrigerating and packaging rooms together with cooked products was not the major cause of spoilage in these products

Use of rRNA Gene Restriction Patterns To Evaluate Lactic Acid Bacterium Contamination of Vacuum-Packaged Sliced Cooked Whole-Meat Product in a Meat Processing Plant

http://aem.asm.org/Molecular typing was applied to an in-plant lactic acid bacterium (LAB) contamination analysis of a vacuum-packaged sliced cooked whole-meat product. A total of 982 LAB isolates from the raw mass, product, and the environment at different production stages were screened by restriction endonuclease (EcoRI and HindIII) analysis. rRNA gene restriction patterns were further determined for different strains obtained from each source. These patterns were used for recognizing the spoilage-causing LAB strains from the product on the sell-by day and tracing the sources and sites of spoilage LAB contamination during the manufacture. LAB typing resulted in 71 different ribotypes, of which 27 were associated with contamination routes. Raw material was distinguished as the source of the major spoilage strains. Contamination of the product surfaces after cooking was shown to be airborne. The removal of the product from the cooking forms was localized as a major site of airborne LAB contamination. Food handlers and some surfaces in contact with the product during the manufacture were also contaminated with the spoilage strains. Some LAB strains were also able to resist cooking in the core of the product bar. These strains may have an effect on the product shelf life by contaminating the slicing machine. The air in the slicing department and adjacent cold room contained very few LAB. Surface-mediated contamination was detected during the slicing and packaging stages. Food handlers also carried strains later found in the packaged product. Molecular typing provided useful information revealing the LAB contamination sources and sites of this product. The production line will be reorganized in accordance with these results to reduce spoilage LAB contamination

Lactobacillus fructivorans spoilage of tomato ketchup

Spoilage characterized by bulging as a result of gas formation in bottled ketchup was studied and resulted in growth on MRS and Rogosa selective Lactobacillus agar. Seventy randomly selected isolates were typed using restriction endonuclease analysis (ClaI, EcoRI, HindIII) and were found to have identical patterns. The strain was identified as Lactobacillus fructivorans using morphological, physiological and biochemical characteristics, combined with information obtained from rRNA gene restriction patterns. Factors affecting growth and survival of this L. fructivorans strain in production circumstances were also studied. Lactobacillus count of 105 CFU/g resulted in spoilage of inoculated ketchup samples. Spoilage occurred only in samples incubated at 15 to 30°C. L. fructivorans implicated in causing spoilage demonstrated heat resistance with a D-value of 1.2 min at 65°C. The strain did not show resistance against alkaline, active chloride containing detergent sanitizer, and also alkyldimethylbenzyl ammonium chloride and alkyldimethylethylbenzyl ammonium chloride containing sanitizer was found to be effective against it