Asymmetric Distribution and Growth of Bacteria in Sliced Vacuum-Packaged Ham and Bologna

Commercially sliced vacuum-packaged cooked ham and bologna were found to contain significantly greater numbers of total and lactic acid bacteria (LAB) on package surface slices than on internal slices. This asymmetric distribution persisted in most samples to beyond the manufacturer's "best before" date. Enterobacteriaceae and bacterial spores were detected infrequently. Bacterial spores were found most often on the surface slices of commercially packaged sliced bologna. Where they occurred, aerobic and anaerobic spores were detected in equal numbers. Center slices of bologna were less hospitable sites for spores and LAB than were surface slices in vacuum packages. When freshly cooked ham and bologna were sliced together with uncooked fermented sausage, LAB from the sausage (pediococci and thermo-tolerant homofermentative lactobacilli) contaminated the cooked meats immediately causing an equal distribution of bacteria throughout the slices. Pediococci did not survive in the vacuum-packaged cooked meats more than 2 weeks at 7°C. The pH of co-sliced bologna prematurely dropped. The shelf life of refrigerated co-sliced ham was reduced by 44%, probably because of adventitious lactobacilli from the sausage. Brochothrix thermosphacta was not present in co-sliced or sliced control meats. Homofermentative lactobacilli predominated in co-sliced and control samples packaged in the laboratory, but in commercially packaged sliced cooked ham and bologna heterofermentative LAB species were dominant. Prolonging cooked ham and bologna shelf life is possible if handling of uncooked fermented sausage is kept separate from the slicing and packaging of cooked cured products.