Minimal processing of iceberg lettuce has no substantial influence on the survival, attachment and internalization of E. coli O157 and Salmonella

VAN DER LINDEN I.; AVALOS LLANO, KARINA ROXANA; ERIKSSON M.; DE VOS W.; VAN DAMME E; UYTTENDAELE M.; DEVLIEGHERE F.

INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2016 vol. 238 p. 40 - 49

0168-1605

The influence of a selection of minimal processing techniques (sanitizing wash prior to packaging, modified atmosphere,storage conditions under light or in the dark) was investigated in relation to the survival of, attachmentto and internalization of enteric pathogens in fresh produce. Cut Iceberg lettuce was chosen as a modelfor fresh produce, Escherichia coli O157:H7 (E. coli O157) and Salmonella enterica were chosen as pathogenmodels. Care was taken to simulate industrial post-harvest processing. A total of 50 ± 0.1 g of fresh-cut Iceberglettuce was packed in bags under near ambient atmospheric air with approximately 21% O2 (NAA) conditions orequilibrium modified atmosphere with 3% O2 (EMAP). Two lettuce pieces inoculated with E. coli O157 BRMSID188 or Salmonella Typhimurium labeled with green fluorescent protein (GFP) were added to each package.The bags with cut lettuce were stored under either dark or light conditions for 2 days at 7 °C. The pathogens´ capacityto attach to the lettuce surface and cut edgewas evaluated 2 days after inoculation using conventional platingtechnique and the internalization of the bacteria was investigated and quantified using confocal microscopy.The effect of a sanitizing wash step (40 mg/L NaClO or 40 mg/L peracetic acid+1143 mg/L lactic acid) of the cutlettuce prior to packaging was evaluated as well. Our results indicate that both pathogens behaved similarlyunder the investigated conditions. Pathogen growth was not observed, nor was there any substantial influenceof the investigated atmospheric conditions or light/dark storage conditions on their attachment/internalization.The pathogens attached to and internalized via cut edges and wounds, from which they were able to penetrateinto the parenchyma. Internalization through the stomata into the parenchyma was not observed, althoughsome bacteria were found in the substomatal cavity. Washing the cut edges with sanitizing agents to reduce entericpathogen numberswas not more effective than a rinse with precooled tapwater prior to packaging. Our resultsconfirm that cut surfaces are the main risk for postharvest attachment and internalization of E. coli O157 andSalmonella during minimal processing and that storage and packaging conditions have no important effect.