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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Bacterial spores dried on aluminium strips are used in microbiological validation of packaging and processing systems. Vortex agitation and sonication in Butterfield's buffer, 70% ethanol or O.lo/o Tween 80 were evaluated for ease of recovery of bacillus spores dried on aluminium strips to compare the concentration of dried spores to dilutions used to inoculate such strips. The highest recovery for Bacillus subtilis var. globigii spores was observed with sonication in 70% ethanol with average recovery close to the initial inoculum. The highest recovery for B. stearothermophilus spores was with sonication in Butterfield's buffer, averaging 0-8 log less recovery than the initial inoculum. Bacillus subtilis var. globigii spores were recovered from strips in greater numbers than B. stearothermophilus spores for all treatment medium combinations. Scanning electron microscopy revealed unrecovered spores adhering to strips after treatment. Recovery of B. subtilis var. globigii spores decreased with time over the 4 week storage period.

INTRODUCTION MATERIALS AND METHODS 101 RESULTS AND DISCUSSION REFERENCES technical bases for legislation on irradiated food (Report of a joint FAO/IAEA/WHO Expert Committee).

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