No abstract

A cocktail made up of six bacteria isolated from fish was subjected to various heats (30°C and 60°C, 20 s) and chemical preservative stresses, alone and in combination. The chemical preservatives tested were potassium sorbate (PS, 1%), trisodium phosphate (TSP, 10%) and tetrasodium pyrophosphate (TSPP, 3%). Heating the bacteria at 60°C for 20 s resulted in an average reduction of 2.0 log cfu/mL in the total number. The results showed a marked synergistic effect of heat treatment prior to chemical additives, especially for TSPP and sorbate; no significant effect was evident when chemicals were applied alone. The effect was increased by the application of chemical preservatives, before heating, in the decreasing order TSP, TSPP and sorbate; reductions obtained were more than 5.0, 4.0 and 3.0 log cfu/mL, respectively. The synergistic effect observed was dependent on the type of chemical additives used and also on the order of the treatments. Bacteria identified as Shewanella putrefaciens and Pseudomonas putida were more resistant to heat treatment and Brochothrix thermosphacta and Lactobacillus plantarum were more resistant to TSP treatment. These bacteria in the cocktail showed high sensitivity to combined TSP/heat treatment; bacterial cells identified as Enterobacter spp. were the most resistant to this treatment.Se preparó una mezcla con seis bacterias aisladas de peces y se sometieron a distintos tratamientos térmicos (30°C y 60°C, 20 s) y de conservantes químicos, por separado y en combinación. Los conservantes químicos empleados fueron sorbato de potassio (PS, 1%), fosfato trisodico (TSP, 10%) y pirofosfato tetrasodico (TSPP, 3%). El calentamiento a 60°C durante 20 s redujo una media de 2.0 log cfu/mL del recuento total de bacterias. Se observó un efecto sinérgico marcado cuando el calor precedía a los tratamientos químicos, de modo más evidente para el TSPP y para el sorbato de potassio; sin embargo no fue significativo el efecto cuando los tratamientos químicos se aplicaron solos. El efecto aumentó cuando los conservantes químicos se aplicaron antes del calor, según el orden decreciente TSP, TSPP y sorbato; las reducciones obtenidas fueron de más de 5.0, 4.0 y 3.0 log cfu/mL, respectivamente. El efecto sinérgico dependió del tipo de aditivo químico y también de la secuencia de los tratamientos. Las bacterias identificadas como Shewanella putrefaciens y Pseudomonas putida fueron las más resistentes al calor; Brochothrix thermosphacta y Lactobacillus plantarum mostraron más resistencia al tratamiento con TSP. Estas bacterias de la mezcla revelaron una alta sensibilidad al tratamiento combinado TSP/calor; las células bacterianas identificadas como Enterobacter spp. fueron las más resistentes a este tratamiento.

A method was developed for the detection and isolation, within a population of lactic acid bacteria, of strains producing exclusively the L-(+)isomer of lactic acid; the visual detection of colonies of these particular strains can be carried out directly on agar plates (50 to 70 colonies per plate). The method is based on an enzymatic stereospecific reaction involving D-(-)-lactate dehydrogenase and linked to a staining reaction; the diffusion area of the D-(-)isomer stains red around the D-(-)and the DL-lactic acid-producing colonies, while the colonies producing exclusively L-(+)-lactic acid are detected by the absence of the colored halo. The intensity of staining was increased when cellulose powder and Tween 20 were added to the agar medium.

The suitability of a microbiological method based on the comparison of an aerobic plate count (APC) with a count obtained with the direct epifluorescent filter technique (DEFT) for the detection of irradiation of deep-frozen foodstuffs was evaluated. The study was carried out on parsley, mechanically deboned poultry meat (MDPM) and liquid egg white. The foodstuffs were stored at -18°C and examined after storage for 0, 4 and 12 months.The results showed that this method is discriminating during the whole storage period.Nevertheless, it has been observed that for non-irradiated liquid egg white the difference between DEFT and APC tends to increase with the time of storage. This phenomenon which did not limit the interest of the test, was not observed for the other products tested.