Survival and growth of naturally occurring or inoculated bacteria were studied in refrigerated (5"C), vacuum-packaged ground pork irradiated at 100 krad (1kGy). Numbers of naturally occurring mesophiles, psycbrotrophs and anaerobes or facultative anaerobes were reduced (PCO.01) by irradiation, whereas lactic acid bacteria were least affected. Partial bacterial recovery during subsequent storage at 5°C suggested sublethal bacterial injury due to irradiation. Irradiation prolonged shelf-life 2.5-3.5 days (3@44%) in uninoculated and l&1.5 days in inoculated (lo5 CFU/g) meat. Added sodium acid pyrophosphate (SAPP) (0.4%) contributed two additional days to inoculated, irradiated pork shelf-life but had no effect on the naturally occurring micrbflora. Lipid oxidation did not increase (P>O.O5) due to irradiation and was unaffected by phosphates.

Bacterial cultures from irradiated (1 kGy) and nonirradiated, vacuumpackaged ground pork held at 5°C were isolated and characterized over a 12-day storage period. The initial flora of the meat was composed mostly of Pseudomonas sp. and Etzterobacter sp. Although the microflora of nonirradiated samples gradually shifted from Gram-negative to Gram-positive microorganisms, 76% of the isolates were characterized as Gram-negative at the onset of spoilage (9 days at 5°C). In contrast, the irradiated ground pork microflora was mainly Grampositive (66%) shortly after irradiation and increased to 97% after 9 days at 5°C. A total of 720 isolates were identified to genus.

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