Effects of processing and storage variables on penetration and survival of Escherichia coli O157:H7 in fresh-cut packaged carrots

The effects of severity of slicing and peeling, and of storage atmosphere and temperature on the survival of Escherichia coli O157:H7 at and below the cut surfaces of fresh-cut carrot discs were determined. Slicing with a blunt machine blade enhanced penetration of E. coli O157:H7 and its subsequent survival during storage at 8 degrees C. Significantly (P < 0.05) higher numbers of cells (0.5 log CFU g(-1)) penetrated deeper (475-500, 725-750 and 975-1000 mu m) into carrot tissue sliced with a blunt machine blade compared to those sliced with a razor blade. Counts on Day 3 and Day 5 of storage remained higher in carrot tissue sliced with a blunt machine blade at all depths sampled. There were no significant effects of peeling method on penetration and survival. Storage of carrot slices in sub-optimal atmospheres (20% CO2/1%O-2 resulted in increased survival of cells at the surface and within the tissue compared to storage in more optimal atmospheres (5% CO2/3% O-2). Increasing storage temperature from 4 to 10 degrees C resulted in growth of E. coli O157:H7 at all sample depths. For all experiments, E. coli O157:H7 cells colonising the surface generally survived better than cells that penetrated into the tissue. The data are relevant to improving microbial safety in the fresh-cut sector by demonstrating that cutting with sharp blades (e.g. during harvesting and processing) reduces the depth of potential contamination by E. coli O157:H7. This may also have implications for more efficient anti-microbial dipping and reduced pathogen survival during storage. (C) 2013 Elsevier Ltd. All rights reserved.