A survey of 36 pairs of new (< 10 days from manufacture) and old (pull date) samples of vacuum-packaged, sliced chopped ham were analyzed for total microbial load, specific pathogen count and pH. Results indicated a wide range of microbial loads, absence of pathogenic bacteria at the levels tested, and presumptive group D streptococci generally < 100/g except for 22% of new samples and 44% of old samples, which had presumptive group D counts > 100 but < 106/g. The survey results also indicated marked differences in pH between products from different manufacturers. Product from two manufacturers was selected for inoculation studies. Chopped ham sandwiches were inoculated with a mixture of five enteropathogenic bacteria and held at 30, 21 and 4 C for up to 24 h. Bacillus cereus, Escherichia coli, Salmonella typhimurium and Staphylococcus aureus, but not Clostridium petfringens, grew in low competition product under the severely abusive holding temperature of 30 C in < 24 h, at 21 C in > 24 h. Product from one manufacturer inhibited the gram negative pathogens. Results indicated that chopped ham in sandwiches required almost unrealistic mishandling to develop a food poisoning potential by enterotoxigenic bacteria, but infective pathogens survived well.

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Author notes

1Supported by funds from Health and Welfare Canada, Research Grants Program.