The role of hydrolases in the loss of firmness and of the changes in sugar content during the post-harvest maturation of Carica papaya L. var solo 8.

Fruit ripening is associated with many hydrolase activities involved in the softening of the fruit during the maturation. This study investigates the relationship between the loss of firmness along with the changes of sugar content and the enzymatic activities in Carica papaya L.var solo 8 during post-harvest storage. Three maturation stages (green immature: the fruit is entirely green, green mature: the fruit shows 1/32 yellow skin and fully mature: the fruit shows 1/8 yellow skin) have been selected and stored at 15, 22 and 28 °C. The reduction of fruit firmness, total sugar contents, refractive index (% Brix) and enzymatic activities were measured. Low enzymatic activities (0.035 µmol/min/mg) were recorded in fruit harvested at the green immature stage with no significant (p ≥ 0.05) effect on the softening while fruit harvested at the green mature and fully mature stages showed enzymatic activities 7 times as high as those of the green immature stage. These high enzymatic activities were responsible for the loss of firmness of the fruit. Accordingly, papayas at the green mature and fully mature stages displayed higher maxima of sugar content (4.8 g/100 g at 28 °C at day 12, and 10.2 g/100 g at 22 °C at day 8, respectively) at higher temperatures. Meanwhile in green immature papayas, the maximum was only 4.3 g/100 g at 22 °C and day 12 of storage. The results show that the loss of firmness of the papaya was highly related to the hydrolytic enzyme activities and the sweet taste to the presence of simple sugars such as galactose liberated from the polysaccharide complexes.

Akwaton, polyhexamethylene-guanidine hydrochloride-based sporicidal disinfectant: a novel tool to fight bacterial spores and nosocomial infections.

Bacterial spores are of continuing interest to the food and medical industries. In efforts to eliminate bacterial spore contamination, a number of sporicidal agents have been developed. Most of these compounds must be used carefully in very specific circumstances as they are toxic to humans. The sporicidal activity of Akwaton, a polyhexamethylene-guanidine hydrochloride (PHMGH)-based disinfectant, was tested against Bacillus subtilis spores. PHMGH is a colourless, odourless, non-corrosive and non-irritating antimicrobial biocide of the guanidine family. Spores suspended in distilled water and spores placed on solid surfaces (stainless steel and glass) were used to determine the log(10) reduction after exposure to varying concentrations of Akwaton. The minimum sporostatic concentration, the minimum sporicidal concentration and the time required for sporicidal activity corresponded to 0.06% (w/v), 0.08 % (w/v) and 8.5 min, respectively. Disinfectant concentrations of 0.24 % (w/v) and 0.44 % (w/v) killed all spores suspended in distilled water within 3 min and 90 s, respectively. The sporicidal activity against suspended spores was linearly dependent with respect to the concentration of PHMGH and contact time (y(3 min) = 40x-1.6 and y(90 s) = 20x-0.8 thus y(3 min) = 2y(90 s)). Spores placed on surfaces were more resistant to the effect of the disinfectant and the positive linear correlation between the sporicidal activity and concentration was not observed. The concentration required to kill all spores placed on a surface (stainless steel or glass) corresponded to 0.52 % (w/v) for 90 s of contact and 0.36 % (w/v) for 3 min. This study demonstrated that PHMGH is an effective sporicidal disinfectant with great potential for use in hospitals, laboratories, food industries and households.

Antimicrobial activities of polyhexamethylene guanidine hydrochloride-based disinfectant against fungi isolated from cocoa beans and reference strains of bacteria.

This study was conducted to assess the antibacterial and the antifungal activity of a polyhexamethylene guanidine hydrochloride (PHMGH)-based disinfectant and to determine if it could be used as a disinfectant for the treatment of cocoa beans. The activity of PHMGH was tested in vitro for efficacy against five reference strains of pathogenic bacteria and six strains of fungi isolated from cocoa beans. All the strains tested were sensitive to the disinfectant. The MICs reported were between 0.01 and 1.9 mg/ml and equal to the MBC or minimum fungicidal concentration (MFC) regardless of the strains of those microorganisms. The bacteria were more sensitive to PHMGH than were the fungi. Enterobacter cloacae was the most sensitive bacterium with a MIC and MBC of 0.01 mg/ml, whereas the genus Aspergillus was the least susceptible of the microorganisms tested, with a MIC and MFC from 1.0 to 1.9 mg/ml. The time required for the activity of PHMGH varies from 2 min for Enterobacter cloacae to 12 min for Aspergillus tamarii and generally increases with the MBC or the MFC. Through this in vitro study, the PHMGH has been proved to be bactericidal and fungicidal on the strains studied. Hence, it could probably serve as a fungicidal disinfectant for the treatment of cocoa beans after harvesting.

Polyhexamethylene guanidine hydrochloride-based disinfectant: a novel tool to fight meticillin-resistant Staphylococcus aureus and nosocomial infections.

Polyhexamethylene guanidine hydrochloride (PHMGH), an antimicrobial biocide of the guanidine family, was tested for efficacy against quality-control strains of Staphylococcus aureus, Pseudomonas aeruginosa, Salmonella choleraesuis, meticillin-resistant S. aureus (MRSA) and Escherichia coli. Bactericidal activity against S. aureus, P. aeruginosa and Salmonella choleraesuis was determined using the official methods of analysis of the Association of Official Analytical Chemists, with modifications as recommended by the Canadian General Standards Board. For MRSA and E. coli, the MIC and minimal bactericidal concentration were determined using the broth dilution technique. The experiments were carried out at 20 degrees C under a range of conditions including varying PHMGH concentration (0.001-0.1 %), contact time (0.5-10 min) and water type (distilled, tap and hard water). The phenol coefficient values determined with S. aureus, Salmonella choleraesuis and P. aeruginosa were 7.5, 6.1 and 5, respectively. No matter what type of water was used to make the dilutions, PHMGH killed MRSA and E. coli at concentrations as low as 0.04 and 0.005 % (w/v), respectively, within 1.5 min. The mode of action of PHMGH was elucidated by transmission electron microscopy: the cell envelope was broken, resulting in cell content leakage into the medium. The ultimate aim of this study was to show that PHMGH can be used as an odourless, colourless, non-corrosive and harmless disinfectant for hospital and household facilities.

Escherichia coli inactivation mechanism by pressurized CO2.

The effects of pressurized CO2 on the survival of Escherichia coli and the mechanism of cell inactivation were studied. Bacterial cultures were inoculated in nutrient broth and incubated at 30 degrees C for 18 h. Exposure of the cells to CO2 under pressures ranging from 2.5 to 25 MPa and at temperatures between 8 and 40 degrees C was performed in a double-walled reactor with a 1 L capacity. The effect of the treatment on the cells was evaluated by plating and by transmission and scanning electron microscopy observation. Vapour CO2 generated a bacteriostatic effect. In liquid or supercritical state, CO2 provided a bactericidal effect. The bactericidal effect increased with pressure and temperature. The mechanism of cell inactivation by liquid CO2 involved two stages. First, cell stress caused by the CO2 penetration provoked cell wall collapse and cellular content precipitation. Second, the cell death caused by supercritical extraction of intracellular substances and cell envelope perforation resulted in leaking of intracellular constituents. In supercritical conditions, the cell inactivation process had one single phase: cellular death.