Antimicrobial activity of essential oils against Staphylococcus aureus biofilms.

The present study was aimed to evaluate the potential of essential oils to remove the foodborne pathogen Staphylococcus aureus from food-processing facilities. The effectiveness of 19 essential oils against planktonic cells of S. aureus was firstly assessed by minimal inhibitory concentration. Planktonic cells showed a wide variability in resistance to essential oils, with thyme oil as the most effective, followed by lemongrass oil and then vetiver oil. The eight essential oils most effective against planktonic cells were subsequently tested against 48-h-old biofilms formed on stainless steel. All essential oils reduced significantly (p < 0.01) the number of viable biofilm cells, but none of them could remove biofilms completely. Thyme and patchouli oils were the most effective, but high concentrations were needed to achieve logarithmic reductions over 4 log CFU/cm(2) after 30 min exposure. Alternatively, the use of sub-lethal doses of thyme oil allowed to slow down biofilm formation and to enhance the efficiency of thyme oil and benzalkonium chloride against biofilms. However, some cellular adaptation to thyme oil was detected. Therefore, essential oil-based treatments should be based on the rotation and combination of different essential oils or with other biocides to prevent the emergence of antimicrobial-resistant strains.

Possible role for cryostabilizers in preventing protein and lipid alterations in frozen-stored minced muscle of Atlantic mackerel.

Adding DE 18 maltodextrin (80 g kg(-1)) to high-fat minced mackerel was highly effective against lipid oxidation and protein and color changes during frozen storage. It increased the temperature of ice-melting onset (Tm') and decreased freeze concentration of solutes in the unfrozen water (UFW) phase, which would have allowed it to effectively slow such perturbations. This maltodextrin showed a higher effectiveness against lipid oxidation, but was slightly less effective in preventing the loss of protein solubility than common cryoprotectants, that is, an equiproportional mixture of sucrose and sorbitol. Such differences in effectiveness were much higher in low-fat minces, in which lipid oxidation proceeded to a much lower extent. Consequently, prior to replacing traditional cryoprotectants with maltodextrins, it should be known which processes limit the shelf life of the food. Decreasing (from 80 to 50 g kg(-1)) the proportion of maltodextrin added to high-fat minced mackerel showed that although it affected only slightly the effectiveness against lipid oxidation, it did notably affect the effectiveness in preventing the loss of protein solubility and color changes. Therefore, such a decrease could be accepted only if lipid oxidation is the most limiting process of shelf life, but does not seem appropriate when protein changes are important.