Quantification of survival and transfer of Salmonella on fresh cucumbers during waxing

Cucumbers found in retail markets are often waxed to improve visual appeal and retard moisture loss. This waxing may affect bacterial survival and the waxing process may facilitate cross-contamination between cucumbers. This study assessed survival of Salmonella on waxed and un-waxed cucumbers and the potential for Salmonella cross-contamination during the waxing process. Fresh waxed or un-waxed cucumbers were spot-inoculated with a Salmonella enterica cocktail. Three different wax coatings (mineral oil, vegetable oil, or petroleum wax) were manually applied to un-waxed cucumbers using polyethylene brushes. Salmonella transfer from inoculated cucumbers to brush or to un-inoculated cucumbers was quantified. Higher Salmonella concentrations were observed on waxed cucumbers during the first 3 days of storage but the final concentration on un-waxed cucumbers was higher than on waxed cucumbers at the end of storage, regardless of storage temperature. Wax formulation did affect survival of Salmonella inoculated directly into waxes, with the significant decline in Salmonella populations observed in vegetable-based wax coating, but with populations unchanged over 7 days at 7 or 21 °C in mineral oil-based and petroleum-based waxes. Salmonella cells could transfer from inoculated un-waxed cucumbers to brushes used for waxing and then to un-inoculated cucumbers during waxing. Significantly higher log percent transfer to brushes was observed when cucumbers were waxed with vegetable oil (0.71 log percent, P = 0.00441) vs. mineral oil (0.06 log percent) or petroleum (0.05 log percent). Transfer to un-inoculated cucumbers via brushes was also quantified (0.18 to 0.35 log percent transfer). Salmonella remaining on contaminated cucumbers after waxing could be detected for up to 7 days, and Salmonella survived better on cucumbers treated with a petroleum-based wax. These findings should be useful in managing risk of Salmonella contamination in cucumbers during post-harvest handling.

MORPHOLOGY AND KINETICS OF PETROLEUM WAX DISSOLUTION IN HYDROCARBON SYSTEMS

This paper studies the effect of solvent chemical nature on the kinetic parameters of dissolution and the morphology of the petroleum waxes. The kinetics of the petroleum wax dissolution in gas condensate and the hexane-cyclohexane-benzene mixture was examined on the torsion balance within the temperature range from 10 to 40°C. The process was described using the Erofeev-Kolmogorov equation. The following kinetic parameters were calculated: reaction rate, the order of reactions and effective energy for activation the wax dissolution in the studied solvents. It was found that the wax dissolution rate in the ternary composite is an order of magnitude greater and the activation energy is three times less in comparison with the process of wax dissolution in the gas condensate. The morphological features of the wax samples, treated by these solvents, were examined by means of scanning electron microscopy. It was found that in the ternary composite, wax has a porous structure and in the gas condensate, it is compressed. Thus, the identified kinetic and morphological behavior of petroleum waxes indicates the influence of the chemical nature of the solvent. The findings of this study can be useful when choosing a solvent for the paraffin deposits removal.