Leaf cuticular waxes of lettuce are associated with reduced attachment of the foodborne pathogen Salmonella spp. at harvest and after postharvest storage

Abstract

The amount and composition of cuticular wax on bolting lettuce leaves of different maturity was shown to be associated with Salmonella attachment and survival. The amount of cuticular wax on leaves from the top (40.9 ± 4.7 μg cm−2) and middle stem (44.7 ± 2.9 μg cm−2) locations was significantly greater than that observed on those from the bottom area (17.5 ± 11.9 μg cm−2). Salmonella attachment was compared between leaves from the middle of the lettuce stem (a visible waxy layer) and mature leaves from the lettuce rosette (lacking with a visible waxy layer) to assess the impact of these crystals. Mature rosette leaves on bolting lettuce showed significantly higher Salmonella attachment (5.72 ± 0.16 CFU g−1) than immature leaves (5.18 ± 0.30 CFU g−1) at harvest. After 7 days of storage at 4 °C, the Salmonella survival rate on mature leaves (5.16 ± 0.23 CFU g−1) was significantly higher (P = 0.01) than that observed on immature leaves (4.38 ± 0.33 CFU g−1). Hexacosanol was identified as the major component of platelet-shaped crystals in the recrystallized wax, which were similar to the wax structures on the lettuce leaf surface. These results suggest that the presence of wax crystals may affect Salmonella attachment on lettuce and that their primary component is hexacosanol.