Applicability of an Arrhenius model for the combined effect of temperature and CO(2) packaging on the spoilage microflora of fish

The temperature behavior of the natural microflora on the Mediterranean fish red mullet (Mullus barbatus) was examined as a case study. The growth of the spoilage bacteria Pseudomonas spp., Shewanella putrefaciens, Brochothrix thermosphacta, and lactic acid bacteria was modeled as a function of temperature and the concentration of carbon dioxide in modified atmosphere packaging. Combined models were developed and comparatively assessed based on polynomial, Belehradek, and Arrhenius equations. The activation energy parameter of the Arrhenius model, E(A), was independent of the packaging atmosphere and ranged from 75 to 85 kJ/mol for the different bacteria, whereas the preexponential constant decreased exponentially with the packaging CO(2) concentration. We evaluated the applicability of the models developed by using experimental bacterial growth rates obtained from 42 independent experiments performed with three Mediterranean fish species and growth rates predicted from the models under the same temperature and packaging conditions. The accuracy factor and bias factor were used as statistical tools for evaluation, and the developed Arrhenius model and the Belehradek model were judged satisfactory overall.     

Lactic acid bacteria population dynamics during spontaneous fermentation of radish (<Emphasis Type="Italic">Raphanus sativus</Emphasis> L.) roots in brine

The aim of the present study was to assess the microecosystem development and the dynamics of the lactic acid bacteria population during spontaneous fermentation of radish (Raphanus sativus L.) roots in brine at 20 and 30?°C. In both temperatures, lactic acid bacteria prevailed the fermentation; as a result, the pH value was reduced to ca. 3.6 and total titrable acidity increased to ca. 0.4% lactic acid. Enterococci population increased and formed a secondary microbiota while pseudomonads, Enterobacteriaceae and yeasts/molds populations were below enumeration limit already before the middle of fermentation. Pediococcus pentosaceus dominated during the first days, followed by Lactobacillus plantarum that prevailed the fermentation until the end. Lactobacillus brevis was also detected during the final days of fermentation. A succession at sub-species level was revealed by the combination of RAPD-PCR and rep-PCR analyses. Glucose and fructose were the main carbohydrates detected in brine and were metabolized into lactic acid, acetic acid and ethanol.     

Applicability of an Arrhenius Model for the Combined Effect of Temperature and CO2 Packaging on the Spoilage Microflora of Fish

The temperature behavior of the natural microflora on the Mediterranean fish red mullet (Mullus barbatus) was examined as a case study. The growth of the spoilage bacteria Pseudomonas spp., Shewanella putrefaciens, Brochothrix thermosphacta, and lactic acid bacteria was modeled as a function of temperature and the concentration of carbon dioxide in modified atmosphere packaging. Combined models were developed and comparatively assessed based on polynomial, Belehradek, and Arrhenius equations. The activation energy parameter of the Arrhenius model, E_A, was independent of the packaging atmosphere and ranged from 75 to 85 kJ/mol for the different bacteria, whereas the preexponential constant decreased exponentially with the packaging CO₂ concentration. We evaluated the applicability of the models developed by using experimental bacterial growth rates obtained from 42 independent experiments performed with three Mediterranean fish species and growth rates predicted from the models under the same temperature and packaging conditions. The accuracy factor and bias factor were used as statistical tools for evaluation, and the developed Arrhenius model and the Belehradek model were judged satisfactory overall.     

Attributes of fresh gilt-head seabream (Sparus aurata) fillets treated with potassium sorbate, sodium gluconate and stored under a modified atmosphere at 0±1°C

The development of microbial populations on fillets of Mediterranean gilt-head sea bream ( Sparus aurata ) treated with potassium sorbate, sodium gluconate or a combination of both and stored under a modified atmosphere (MA) of 40% CO₂, 30% O₂ and 30% N₂ at 0±1 °C for about 30 d was studied. The pH of aqueous solutions of the preservatives was adjusted to 6·0 with HCl. The preservatives were applied by dipping. The use of sorbate plus gluconate was more effective than sorbate alone. Gluconate had a positive effect on the growth of Gram-positive micro-organisms. Changes in the concentrations of glucose, glucose-6-phosphate, ammonia, acetic acid, trimethylamine-nitrogen and sorbate were also monitored.     

Weak antimicrobial effect of carob (Ceratonia siliqua) extract against food-related bacteria in culture media and model food systems

A weak antibiotic effect of carob (Ceratonia siliqua) extract against Staphylococcus aureus S-6, St. aureus 722, and Pseudomonas fragi, was evident when the strains were screened with the paper disk assay. An intermediate inhibitory action of carob on Listeria monocytogenes, Salmonella enteritidis, and Brochothrix thermosphacta was found with the same technique while Shewanella putrefaciens was not inhibited. The inhibitory action of extract against St. aureus and P. fragi was also confirmed in broth culture while little effect was noted with S. enteritidis. The addition of extract to tuna and potato salad stored under aerobic and modified atmosphere packaging conditions at 4 °C, affected the survival of St. aureus but not that of S. enteritidis.     

A preparative suspension culture system permitting quantitation of anchorage-independent growth by direct radiolabeling of cellular DNA

We have developed a hybrid methylcellulose/agar suspension culture system which permits long-term colony formation of transformed mesenchymal cells. In contrast to traditional agar suspensions, our system allows for recovery of cells and direct biochemical analysis of anchorage-independent growth. The ability to readily radiolabel cellular macromolecules in these preparative cultures permits a quantitative and objective analysis of colony formation by incorporation of [3H]thymidine into newly synthesized DNA.     

Influence of nutrients on growth and bacteriocin production by Leuconostoc mesenteroides L124 and Lactobacillus curvatus L442

The aim of this study was to investigate the effect of complex nutrients on microbial growth and bacteriocin production, in order to improve bacteriocin synthesis during the growth cycle of Leuconostoc mesenteroides L124 and Lactobacillus curvatus L442. The fermentations were conducted at the optimum pH and temperature for bacteriocin production (pH 5.5+/-0.1 and temperature 25+/-0.1 degrees C). Because of their association with the final biomass, conditions favouring the increase of the produced biomass resulted in the increase of bacteriocin activity in the growth medium. Since the produced final biomass and the final concentration of the bacteriocins were associated with the amount of the carbon (glucose) and nitrogen source, better growth of the lactic acid bacterial strains favoured the increase of the specific bacteriocin production. Additionally, the bacteriocin production was influenced by carbon/nitrogen ratio.     

Growth of Listeria monocytogenes in meat juice under a modified atmosphere at 4°C with or without members of a microbial association from chilled lamb under a modified atmosphere

Listeria monocytogenes together with Gram-positive and Gram-negative bacteria was grown in axenic cultures in meat juice under an atmosphere enriched with carbon dioxide at 4°C. The size of the final population of listeriae was determined by that of the initial inoculum. Growth of L. monocytogenes ceased with glucose depletion. Glucose-6-phosphate was not catabolized by listeriae. In aerobic axenic cultures generation times of L. monocytogenes were shorter and glucose depletion was faster than with a carbon dioxide-enriched atmosphere. Oxidation of L- and D-lactic to acetic acid was probably associated with the subsequent die-off of L. monocytogenes.