2018 ASHS Annual Conference
Food Pathogen Attachment on Different Level of Epicuticular Wax Surface of Vegetables
Food Pathogen Attachment on Different Level of Epicuticular Wax Surface of Vegetables
Thursday, August 2, 2018: 10:00 AM
Lincoln East (Washington Hilton)
Although understanding attachment mechanism of Salmonella to produce surface is crucial information for reducing food pathogen outbreak, the bacterial attachment to different surface properties of leaves is not fully understood. Epicuticular wax is the most outer layer on the leaf surface that directly interact with food pathogen attachment. The hydrophobic nature of epicuticular wax has been found to have positive attributes to pathogen resistance due to the prevention of spore germination, however, there is limited study on if the amount of epicuticular wax layer on the leaf is correlated with the attachment ability of Salmonella. The goal of this study is to examine attachment strength of Salmonella on various leafy vegetable surface including collard green cultivars (‘Green glaze’ as glossy leaf type and ‘Top Bunch’ as waxy leaf type (Brassica oleraceae L. Acephala group), two sets of broccoli isogenic (USDA115 glossy and waxy; USDA188 glossy and waxy), and flowering lettuce. The leaf surface image of all vegetables examined by scanning electron micrographs (SEM) showed the topographical difference; net-like waxy crystals were deposited on ‘Top Bunch’ and waxy broccoli (USDA188 and USDA115) leaf surface and the waxy layer made less visible stomata compared to glossy collard ‘Green Glaze’ and glossy broccoli (USDA188 and USDA115). Characteristic of crystalline wax structures on lettuce leaf epidermis was platelets with few needles. Total wax content of waxy collard was 94.85±7.41 μg/cm^2 with total fatty acids concentration 24.1 μg/cm^2, total alkanes 776.6 μg/cm2, total alcohol 96.1 μg/cm2 and total ketone 394.3 μg/cm^2. By contrast, total wax content of glossy collard was 2.31±0.39 μg/cm2 with total fatty acid concentration 22.6 24.1 μg/mL, total alkanes 2.8 μg/mL, total alcohol 6.1 μg/mL and non-detectable ketone concentration. The total amount of epicuticular wax on apical and middle attached leaves of flowering stem in lettuce had about six fold higher than lower leaves (31 -39 µg/cm^2). The attachment of Salmonella was significantly stronger on the glossy collard (10^5 CFU/g) rather than the waxy collard (10^4 CFU/g). The different Salmonella attachment was maintained during postharvest storage. We also confirm the same trend using broccoli isogenic lines and flowering lettuce model. To confirm the epicuticular wax effect on Salmonella attachment, epicuticular waxes were removed by arabic gum treatment and test the Salmonella attachment. Salmonella attachment was significantly increased after epicuticular wax removal. These results suggest the presence of epicuticular wax has negatively influence on Salmonella attachment and the cultivar chosen for the salad leaves can potentially be considered to reduce the risk of foodborne contamination during pre-harvest and post-harvest condition.