J. Metaxopoulos

Characterization of the microbial flora from a traditional Greek fermented sausage

The microbial flora of naturally fermented sausages was studied. Lactic acid bacteria were the dominant species at the end of fermentation in all 3 batches (ca. 10(8) cfu g(-1)). Enterobacteria, Pseudomonas, yeasts and aerobic spore-formers decreased during fermentation and the ripening process and were below the detection limit in the end product. Enterococci exceeded 10(4)-10(5) cfu g(-1) during fermentation and remained constant at this level during ripening. Gram-positive, catalase-positive cocci exceeded 10(5) cfu g(-1), except for batch 1, during the first days of fermentation and then decreased until the end of ripening (10(2)-10(4) cfu g(-1)). No pathogenic staphylococci, sulfite reducing clostridia or Salmonella spp. were detected. Listeria spp. occurred in the first days of fermentation but were eliminated by the end of whole process in all batches. Identification showed that the majority of lactobacilli isolated from MRS agar strains were assigned to the species of Lactobacillus plantarum and Lb. plantarum/pentosus. All the isolated strains from the mannitol salt agar belonged to the genus of Staphylococcus. The predominant species were Staphylococcus saprophyticus, Staphylococcus xylosus and Staphylococcus simulans. The tests used to characterize the lactic acid bacteria and staphylococci as well as their distribution on the three batches were also discussed.

Characterisation of lactic acid bacteria isolated from naturally fermented Greek dry salami.

A total of 348 lactic acid bacteria isolated from five batches of naturally fermented dry salami at various stages of ripening were characterised. The majority of the strains were assigned to two main phylogenetic groups of species: (i) the psychrotrophic, formerly called atypical, meat streptobacteria (169 strains) and (ii) a new genus Weissella (120), which was recently proposed (Collins et al., 1993) to include Leuconostoc paramesenteroides and some other closely related species. Meat streptobacteria were identified as Lactobacillus curvatus (88 strains) and L. sake (76), whereas 5 strains were indistinguishable and, thus designated L. sake/curvatus. Non-psychrotrophic streptobacteria were also isolated and identified as L. plantarum (34 strains), L. farciminis (10), L. coryniformis (1) and L. casei subsp. pseudoplantarum (1). The majority of the Weissella strains (86) were leuconostoc-like bacteria; four of them were identified as W. viridescens, 11 belonged to the newly described W. hellenica (Collins et al., 1993), another 11 resembled W. paramesenteroides, whereas 60 isolates were not classified to any species. The latter group comprised strains that produced D(L)-lactate. The remaining Weissella were gas-forming, arginine-positive rods assigned to W. minor (31) and W. halotolerans (3). Other species identified were Enterococcus faecium (10), Leuconostoc mesenteroides (1), L. brevis (1) and Pediococcus sp. (1). The main criteria used to distinguish between above species as well as their distribution on the five salami batches in relation to their succession with time and suitability as starters were discussed.

Evaluation of the extent and type of bacterial contamination at different stages of processing of cooked ham

In an attempt to determine the composition and origin of the spoilage flora of refrigerated vacuum‐packed cooked ham, the changes in microbial numbers and types were followed along the processing line. Results revealed Lactobacillus sake and Leuconostoc mesenteroides ssp. mesenteroides as the major causative agents of spoilage of sliced ham stored at 4 °C and 12 °C, due to recontamination in the cutting room. On the contrary, the progressive deterioration of whole ham under the same storage conditions was associated with a non‐identifiable group of leuconostoc‐like bacteria. Except for lactic acid bacteria, no other organism grew in vacuum packs of either sliced or whole ham. Although atypical leuconostocs could not be detected among isolates recovered from freshly produced whole ham, they appeared to survive cooking and proliferate during storage. Neither these organisms however, nor Lact. sake and Leuc. mesenteroides were important in curing and tumbling as carnobacteria, mainly Carnobacterium divergens, and Brochothrix thermosphacta dominated at this stage. A progressive inversion of the ham microflora from mostly Gram‐negative at the beginning of processing to highly Gram‐positive prior to cooking was noted. Listeria monocytogenes cross‐contaminated ham during tumbling. However, the pathogen was always absent from the vacuum‐packed product provided that heating to a core temperature of 70 °C occurred and recontamination during slicing and packing was prevented. The percentage distribution of different species of lactic acid bacteria as well as the uncommon phenotypic characteristics of some strains were discussed.

Lipolytic and microbial changes during the natural fermentation and ripening of Greek dry sausages.

The hydrolytic changes in the lipid fraction and the changes in microbial growth during the natural fermentation and ripening of Greek dry sausages were studied. Two batches were manufactured under industrial conditions, without the addition of starter cultures. The results of the microbiological analyses indicated that, among the micro-organisms well known for their lipolytic activity, micrococci were predominant during the whole fermentation-ripening process. It was shown that the fatty acid composition of the hydrolysed lipid fraction did not remain constant with time. Analysis of the experimental results indicated that, given the length of the aliphatic chain (16 or 18 carbon atoms), the more unsaturated fatty acids were hydrolysed in preference to the saturated homologues. On the other hand, fatty acids having 16 carbon atoms were hydrolysed in preference to the iso-unsaturated ones having 18 carbon atoms.

Growth and bacteriocin production kinetics of Leuconostoc mesenteroides E131

Aims:  The aim of this study was to investigate the effect of pH, temperature, sodium chloride, type and level of sugar used in fermented sausages, on the occurrence and the concentration of the maximum bacteriocin activity, in order to optimize the bacteriocin synthesis during the growth cycle of Leuconostoc mesenteroides E131.

Modeling of growth and bacteriocin production by Leuconostoc mesenteroides E131.

Leuconostoc mesenteroides E131, isolated from dry fermented sausages, produces an antimicrobial agent, characterized as bacteriocin. The effect of pH and temperature on growth and bacteriocin production, using MRS broth as growth medium, was studied in a fermentor. The pH value at which the best cell growth was observed (6.5) did not coincided with the value at which the maximum bacteriocin activity was attained (5.5). In contrast, the maximum bacteriocin activity was attained at temperature (25°C) close to the optimum temperature for cell growth (25-30°C). Notably, the range of pH and temperature for good bacteriocin production was within the range used for sausage fermentation. An empirical model was developed to describe the growth and bacteriocin production in different pH and temperature conditions. The model was able to describe growth and bacteriocin production and it could be used to predict the kinetic parameters of growth and bacteriocin production within the pH and temperature range examined.

A novel modelling approach for predicting microbial growth in a raw cured meat product stored at 3°C and at 12°C in air

To predict microbial growth during chill storage of a traditional Greek raw sausage, a numerical model was developed and validated. In our novel approach, the specific growth rate of each microbial population was calculated on the basis of the main microbial populations grown in the sausage. In addition, the specific destructive effect of the sausage ecosystem was introduced to evaluate microbial growth. The model was integrated by the Runge-Kutta method and the parameter values were optimised by the least squares method. Fitting of the model to the experimental data derived from four sausage batches stored aerobically at 3 and 12°C successfully described the microbial growth kinetics in the sausage niche. Finally, the parameter values estimated by the fitting of the model on the data set from each batch were used to predict microbial growth in the other batches at both storage temperatures.

Atypical Leuconostoc-like Weissella Strains isolated from Meat, Sharing Low Phenotypic Relatedness with the so far Recognized Arginine-negative Weissella spp. as Revealed by SDS-PAGE of Whole Cell Proteins

Summary The levels of phenotypic relatedness among 34 atypical, arginine-negative Weissella strains isolated from naturally fermented Greek dry salami and the species Weissella paramesenteroides (type strain), Weissella hellenica (five strains including type strain), Weissella viridescens (four strains and a reference strain) and Leuconostoc mesenteroides subsp. mesenteroides (one strain) were determined by numerical analysis of whole cell protein profiles. W. paramesenteroides was phenotypically more closely related to Lc. mesenteroides rather than to W. hellenica and W. viridescens. Clearly separated from these four species, atypical Weissella strains formed three distinct clusters, which were also of low phenotypic similarity to each other. Two of the clusters were tight and comprised strains capable of producing solely D-lactate. The third cluster was very diverse as consisted of four subgroups and an “intruder” strain. Most strains of this cluster formed D(L)-lactate. Based on the SDS-PAGE findings, evidence was provided that atypical sausage isolates may represent new, unidentified Weissella taxons of meat origin.