2017 ASHS Annual Conference
Difference in Attachment of Salmonella enterica to Waxy or Glossy Collard Leaves
Difference in Attachment of Salmonella enterica to Waxy or Glossy Collard Leaves
Thursday, September 21, 2017
Kona Ballroom (Hilton Waikoloa Village)
Although understanding attachment mechanism of Salmonella to produce surface is crucial information for reducing food pathogen outbreaks, 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 collard green cultivars (‘Green glaze’ as glossy leaf type and ‘Top Bunch’ as waxy leaf type (Brassica oleraceae L. Acephala group). The leaf surface image of two cultivars examined by scanning electron micrographs (SEM) showed the topographical difference; net-like waxy crystals were deposited on ‘Top Bunch’ leaf surface and the waxy layer made less visible stomata compared to glossy collard ‘Green Glaze’. ‘Top Bunch’ collard has significantly higher contact angle (147°±6.21) than ‘Green Glaze’ (89°±2.11), indicating that the higher surface hydrophobicity. Total wax content of waxy collard was 94.85±7.41 μg/cm2 with total fatty acids concentration 1.8 μg/cm2, total alkanes 57.1 μg/cm2, total alcohol 7.1 μg/cm2 and total ketone 29 μg/cm2. By contrast, total wax content of glossy collard was 2.31±0.39 μg/cm2 with total fatty acid concentration 1.7 μg/cm2, total alkanes 0.2 μg/cm2, total alcohol 0.4 μg/cm2 and non-detectable ketone concentration. The most significant difference of wax composition of glossy type collard ‘Green Glaze’ compared to waxy type collard was absence of 1-hexadecanol, 15-nonacosanone (C29 ketone) and C31 alkane. In addition, the concentration of C29 alkane in waxy collard was significantly (P<0.001) higher than glossy type with 190-fold increment. The attachment of Salmonella was significantly stronger on the glossy collard (105 CFU/g) rather than the waxy collard (104 CFU/g). The preliminary result suggests 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 illness.