Effects of Irradiation Dose and O₂ and CO₂ Concentrations in Packages on Foodborne Pathogenic Bacteria and Quality of Ready-to-Cook Seasoned Ground Beef Product (Meatball) during Refrigerated Storage

Table 1

Changes in S. enteritidis, L. monocytogenes, and E. coli O157:H7 counts (Log CFU g⁻¹) in ready-to-cook meatballs during storage at 3°C as affected by irradiation dose (kGy) and O₂ levels in 0% CO₂ containing packages.

Storage (day)	O2*	S. enteritidis			L. monocytogenes			E. coli O157:H7
	(%)	0 kGy	2 kGy	4 kGy	0 kGy	2 kGy	4 kGy	0 kGy	2 kGy	4 kGy
1	0	6.61^d,x	3.22^ab,y	<2.0	6.60^e,x	2.60^d,y	<2.0	4.85^e,x	<2.0	<2.0
	5	6.65^cd,x	3.04^b,y	<2.0	7.00^bc,x	2.33^e,y	<2.0	5.57^d,x	<2.0	<2.0
	21	6.93^a,x	2.28^f,y	<2.0	6.97^cd,x	2.54^d,y	<2.0	5.95^cd,x	<2.0	<2.0
7	0	6.70^bcd,x	3.03^b,y	<2.0	6.85^d,x	2.97^b,y	<2.0	6.13^c,x	<2.0	<2.0
	5	6.87^ab,x	2.74^cd,y	<2.0	7.00^bc,x	2.89^bc,y	<2.0	5.98^c,x	<2.0	<2.0
	21	6.64^d,x	2.43^ef,y	<2.0	7.11^ab,x	2.07^f,y	<2.0	6.32^bc,x	<2.0	<2.0
14	0	6.86^abc,x	3.25^a,y	<2.0	7.07^bc,x	3.22^a,y	<2.0	6.82^a,x	<2.0	<2.0
	5	6.63^d,x	2.81^c,y	<2.0	7.02^bc,x	3.13^a,y	<2.0	6.69^ab,x	<2.0	<2.0
	21	6.86^abc,x	2.58^de,y	<2.0	7.21^a,x	2.80^c,y	<2.0	6.88^a,x	<2.0	<2.0

Values with different superscript letters (a–f) within a column differ significantly (𝑃<0.05).
Values with different superscript letters (x–y) within a row for each pathogen differ significantly (𝑃<0.05).
<2.0: below detection limit.
*Target O₂ levels in the original packages.