Vinegar production from Togolese local variety Mangovi of Mango mangifera indica Linn. (Anacardiaceae).

The present study aimed to access for the physiochemical parameters of vinegar production through Togolese local variety Mangovi of mango Mangifera indica juice fermentation. The juice was fermented successively by Saccharomyces cerevisisae and acetic bacteria. The levels of ethanol and acetic acid in the juice during the production of vinegar were monitored by gas chromatography and titrimetry methods, respectively. The physiological state of the yeast Saccharomyces cerevisiae L2056 was determined by flow cytometry using a dual fluorescent labeling of diacetate carboxy-fluorescein (CFDA) and propidium iodide. The results indicated that 200 mL of mango juice, sugar content 20 Brix, set in alcoholic fermentation with 10(6) yeast cells produced 22.4 g L(-1) ethanol in 72 h. Acetic fermentation transformed 93% of this ethanol to acetic acid in 288 h. Twenty-four hours after the beginning of alcoholic fermentation, 91% of cells were viable, 8.85% were stressed and 0.05% died. After 24 h of acetic fermentation, viable, stressed and dead cells were 45, 12 and 39%, respectively; corresponding to the passage of acetic vinegar level from 0.9 to 2.1 degrees. At the end of the acetic fermentation, dead cells were estimated to 98% at and acetic acid to 4.7 degrees. Using consecutive fermentations is suitable technique for vinegar production from mango juice. The application of the present results may contribute to avoid fruits post harvest losses.

Tunisian Salvia officinalis L. and Schinus molle L. essential oils: their chemical compositions and their preservative effects against Salmonella inoculated in minced beef meat.

The essential oils (EOs) extracted from the aerial parts of cultivated Salvia officinalis L. and the berries of Schinus molle L. were analysed by gas chromatography-mass spectrometry (GC-MS) and 68 and 67 constituents were identified, respectively. The major constituents were 1,8-cineole (33.27%), beta-thujone (18.40%), alpha-thujone (13.45%), borneol (7.39%) in S. officinalis oil and alpha-phellandrene (35.86%), beta-phellandrene (29.3%), beta-pinene (15.68%), p-cymene (5.43%) and alpha-pinene (5.22%) in S. molle oil. In its second part, the present study was conducted to evaluate the in vitro antimicrobial activity of both studied EOs. For this purpose, paper disc-diffusion method and broth microdilution test were used. The disc-diffusion method showed significant zone of lysis against all the pathogens studied (gram-negative and gram-positive bacteria, yeast). These activities remained stable after six months, and decreased approximately by 20% after one year of storage of the EOs at 4 to 7 degrees C. On comparing the efficiency of both EOs, S. officinalis EO exhibited higher antibacterial activity against the majority of strains and especially against Candida albicans (two fold more active according to the inhibition zones values). The minimal inhibitory concentrations (MICs) were reported between 4.5 mg/ml and 72 mg/ml on nutrient broth. The particular chemotype of each EO may be involved in its specific antimicrobial behaviour. Furthermore, the inhibitory effect of these EOs were evaluated against two foodborne pathogens belonging to Salmonella genus, experimentally inoculated (10(3) CFU/g) in minced beef meat, which was mixed with different concentrations of the EO and stored at 4 to 7 degrees C for 15 days. Although the antibacterial activities of both EOs in minced beef meat were clearly evident, their addition had notable effects on the flavour and taste of the meat at concentrations more than 2% for S. molle and 1.5% for S. officinalis. One solution to the above-mentioned problem may be the use of combinations of different food preservation systems. In this context, each of the EOs has been used along with low water activity (addition of NaCl) in addition to low refrigeration temperatures. Results on the Salmonella growth showed that some combinations could be recommended to eliminate germs from minced raw beef. By using this method, a stable and, from a microbiological point of view, safe meat can be produced without substantial loss in sensory quality. Results obtained herein, may suggest that the EOs of S. officinalis and S. molle possess antimicrobial activity, and therefore, they can be used in biotechnological fields as natural preservative ingredients in food and/or pharmaceutical industry.

[Polygalacturonase enzyme production from bacterial isolated from raw milk and green and black olives]. / Production d'enzyme polygalacturonase par des souches microbiennes isolées du lait cru et des olives noires et vertes.

Forty microbial strains isolated from raw milk samples and black and green olives were grown in MP5 (mineral pectin 5) medium containing 0.5% lemon pectin. All strains synthesized an extracellular polygalacturonase. Rhodotorula sp. ONRh9 (0.44 U x mL(-1)) and Leuconostoc sp. LLn1 (0.16 U x mL(-1)), which had a more active polygalacturonase in MP5 medium, were studied in MAPG5 medium containing polygalacturonic acid. Highest biomass and polygalacturonase production by these two strains were observed for polygalacturonic acid concentrations of 10 g x L(-1) (Rhodotorula sp. ONRh9) and 5 g x L(-1) (Leuconostoc sp. LLn1) and for initial pH values of 6 (Rhodotorula sp. ONRh9) and 5.5 (Leuconostoc sp. LLn1). The two strains grown in fermenters in MAPG5 medium generated the following results: with controlled initial pH, Rhodotorula sp. produced maximum biomass (DO) and polygalacturonase (PG) after 20 h (DO, 3.86; PG, 0.24 U x mL(-1)) of growth, and this level was sustained until the end of the culture; Leuconostoc sp. LLn1 synthesized more cells and polygalacturonase between 4 h (DO, 1.80; PG, 0.17 U x mL(-1)) and 24 h (DO, 3.90; PG, 0.27 U x mL(-1)) of culture. With uncontrolled initial pH, the cultures produced maximum biomass and polygalacturonase after 20 h (DO, 3.30; PG, 0.26 U x mL(-1)) for Rhodotorula sp. ONRh9 and 10 h (DO, 2.84; PG, 0.17 U x mL(-1)) for Leuconostoc sp. LLn1.

Intracellular physiological events of yeast Rhodotorula glutinis during storage at +4 degrees C.

Samples of the cheese yeast Rhodotorula glutinis were analysed during storage at +4 degrees C for cultivability, viability, vitality (metabolic activity), membrane potential state, intracellular pH, and carbohydrate content. The results have allowed to describe cellular events occurring during storage. The loss of vitality came with the decrease of carbohydrate content. The fall of trehalose content under a threshold value induced the deterioration of the membrane potential. Later, when all the cells were depolarised, the intracellular pH decreased and the cultivability dropped, whereas viable cells still decreased slowly. Then, it led to an intermediate physiological state similar to the viable but non-cultivable state. Finally, the fall of viability dropped. In this work, we have defined rapid methods relevant to describe the sequence of intracellular events in the cheese yeast R. glutinis during storage, and we applied them to understand the weak vitality without fall of viability of yeast samples. These methods might allow to rapidly test yeast sample quality before use and to predict, at the moment of the harvesting, the conservation of the yeast.

Raw cow milk bacterial population shifts attributable to refrigeration.

We monitored the dynamic changes in the bacterial population in milk associated with refrigeration. Direct analyses of DNA by using temporal temperature gel electrophoresis (TTGE) and denaturing gradient gel electrophoresis (DGGE) allowed us to make accurate species assignments for bacteria with low-GC-content (low-GC%) (<55%) and medium- or high-GC% (>55%) genomes, respectively. We examined raw milk samples before and after 24-h conservation at 4 degrees C. Bacterial identification was facilitated by comparison with an extensive bacterial reference database ( approximately 150 species) that we established with DNA fragments of pure bacterial strains. Cloning and sequencing of fragments missing from the database were used to achieve complete species identification. Considerable evolution of bacterial populations occurred during conservation at 4 degrees C. TTGE and DGGE are shown to be a powerful tool for identifying the main bacterial species of the raw milk samples and for monitoring changes in bacterial populations during conservation at 4 degrees C. The emergence of psychrotrophic bacteria such as Listeria spp. or Aeromonas hydrophila is demonstrated.

Resistance of spheroplasts and whole cells of Pseudomonas aeruginosa to bactericidal activity of various biocides: evidence of the membrane implication.

To emphasise the role of outer and inner membranes in the resistance of Pseudomonas aeruginosa to bactericidal activity of various disinfectants, spheroplasts and whole cells were compared. Spheroplasts are more sensitive than whole cells to quaternary ammonium compounds such as didecyl dimethyl ammonium bromide (DDAB) and C16-benzalkonium chloride. The outer membrane acts as a barrier to prevent these disinfectants from entering the cell. It seems to have no influence on activities of smaller molecules such as C12, C14-benzalkonium chlorides and sodium dichloroisocyanurate. For tri-sodium phosphate, the presence of outer membrane emphasized the action of the molecule. Moreover, resistance of DDAB-adapted spheroplasts to bactericidal activity of DDAB is higher than the resistance of non-adapted spheroplasts. This suggests that the inner membrane could also play a role in resistance to DDAB.

Cold adaptation of Escherichia coli: microbiological and proteomic approaches.

The aim of this work was to use two approaches (microbiological and proteomic) to study the effect of cold adaptation (3 h at 4 degrees C) on the survival of two Escherichia coli strains, I2 and R3, following freezing at -20 degrees C for 24 h and thawing for 45 min at 37 degrees C. The effect of cold adaptation on cell survival after freezing was determined by measuring viable counts on selective (PTX) and nonselective media (TSA). The beneficial effect of the cold treatment was more pronounced for the freezing-sensitive R3 strain: Prior to adaptation, differences between the two media were 3.5 log10 for R3 and 0.4 log10 for I2. After adaptation, the differences were 2.5 log10 and 0.1 log10 for R3 and I2, respectively. The proteins from two cell compartments, cytoplasm and outer membrane, were separated by two-dimensional electrophoresis and identified by mass spectrometry or Edman sequencing. The adaptation resulted in changes in the expression of certain proteins. Among the principal changes to protein profiles in strain R3 following cold adaptation, we observed an over-expression of the EF-TU elongation factor in the outer membrane, and an under-expression of flagellin (FLIC) in the cytoplasm. Very few changes were observed in strain I2.