Mouna Boulares

Study of the microbial ecology of wild and aquacultured Tunisian fresh fish.

Eighty samples of fresh fish were collected in Tunisia and analyzed for microbial load. Quality and hygienic safety of the meat and intestines of wild and aquacultured fresh fish were determined. The mesophilic aerobic plate count and populations of psychrotrophic lactic acid bacteria (LAB) and other psychrotrophic bacteria ranged from 5.67 to 7.29, 4.51 to 6, and 5.07 to 6.21 log CFU/g, respectively. For all microbiological determinations, bacterial counts were lower in meat than in the intestines of fresh fish. For all samples lower microbial populations were found in most of the wild fish than in the aquacultured fish. No isolates of the pathogenic genera Salmonella and Listeria were detected in any sample. Among the 160 strains of biopreservative psychrotrophic LAB and the 150 strains of spoilage psychrotrophic gram-negative bacteria identified by biochemical and molecular methods, Lactobacillus (six species) and Pseudomonas (six species) predominated. Lactococcus, Leuconostoc, Carnobacterium (C. piscicola and C. divergens), Aeromonas, and Photobacterium were the most common genera, and Lactococcus lactis, Lactobacillus plantarum, Pseudomonas fluorescens, and Aeromonas hydrophila were the most common species. These findings indicate that the microbiological quality of fresh fish in Tunisia can be preserved by controlling pathogenic and psychrotrophic bacteria.

Characterisation and technological properties of psychotropic lactic acid bacteria strains isolated from Tunisian raw milk

A total of 102 wild lactic acid bacteria (LAB: 32%Lactococcus ssp.lactis, 23%Lactobacillus plantarum, 22%Lactobacillus pentosus, 7%Leuconostoc mesenteroides, 5%Lactobacillus brevis), isolated from Tunisian refrigerated raw milk obtained from collected centres, were screened according to their antimicrobial activities against spoilage and undesirable micro-organisms. Nineteen isolates having the most important antimicrobial activities were selected. Amplification of 16S/23S spacer regions of these selected LAB yielded two amplicons forLactobacillus genus and only one amplicon for bothLactococcus andLeuconostoc. However, three strains ofLactococcus and two strains ofLeuconostoc were eliminated because they present two amplicons. Hence, only fourteen strains were retained, they were also characterised in respect to their technological properties (lipolytic activities, proteolytic activities, enzymatic activities, acidifying capacity and antibiotic resistance). Acidification (degree Dornic) varied from 24.5±0.07 to 37.5±0.07 after 10 h. Low proteolytic capacity was detected for all strains using different substrates (oPA, TNBS and azocasein methods). Lipolytic capacity didn’t surpass 0.3±0.03% fatty acids for all strains. Lipase and esterase lipase activities were practically non-existent for most selected LAB. The behaviour of these strains against various antibiotics was also found to be similar.

Effects of Lactic Acid Bacteria and Citrus Essential Oil on the Quality of Vacuum-Packed Sea Bass (Dicentrarchus labrax) Fillets During Refrigerated Storage

ABSTRACT The preservative effect of refrigerated and vacuum-packed sea bass (Dicentrarchus labrax) fillets inoculated with four mixtures of lactic acid bacteria (LAB) (Lactococcus lactis, Lactobacillus plantarum, and Carnobacterium piscicola) and incorporated with citrus essential oil (CEO) was evaluated on the basis of microbiological and biochemical analysis. Initially, sea bass fillets showed high nutritional quality. During refrigerated storage, lipid contents did not show a significant decrease in any fish fillets; meanwhile, important proteolysis was observed in untreated control. In addition, results indicated that both CEO and LAB strains exhibited antimicrobial activity against spoilage, pathogenic, and fungi flora. Moreover, the total volatile bases (TVB-N) values were higher in control fillets, and the lowest TVB-N values were observed in Control CEO and C3 + CEO (30.47 ± 0.00 and 32.29 ± 1.12 mg TVB-N/100 g, respectively). Also, the levels of biogenic amines increased in all fillets without exceeding the upper limit of acceptability except for untreated control (sum of about 1396.63 ppm). Furthermore, this combined treatment ameliorated the muscle liquid-holding capacity, which improves technological properties. Overall, this treatment may open new promising opportunities for the biopreservation of fish products by enhancing the period of storage of refrigerated and vacuum-packed sea bass fillets.

Effect of commercial starter cultures on physicochemical, microbiological and textural characteristics of a traditional dry fermented sausage reformulated with camel meat and hump fat

In this work, a mixture of Staphylococcus carnosus and Lactobacillus sakei was used for the manufacture of a traditional dry fermented sausage reformulated with camel meat and hump fat. Changes of microbiological, biochemical, sensorial and textural characteristics during the ripening of sausages were investigated. The lactic acid bacteria count was significantly higher at day 7 of ripening in inoculated sausages and was accompanied by a lower pH. Proteolysis and lipolysis were observed both in control and in inoculated sausages; however, these activities during ripening could be due to the activity of starter culture enzymes or the activity of meat endogenous enzymes. Sensory profile analysis revealed significant differences in hardness, acidity and color intensity. Finally, the texture analysis showed clear differences, with the inoculated batch being less hard.