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 2

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 irradiation dose (kGy) and O₂ level in 50% 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	6.56^d,x	3.07^b,y	<2.0	6.92^b,x	2.57^d,y	<2.0	5.15^c,x	<2.0	<2.0
	5	6.59^cd,x	2.24^e,y	<2.0	6.94^ab,x	2.50^d,y	<2.0	5.51^c,x	<2.0	<2.0
	21	6.81^ab,x	2.19^e,y	<2.0	7.05^ab,x	2.54^d,y	<2.0	5.47^c,x	<2.0	<2.0
7	0	6.83^ab,x	3.05^b,y	<2.0	6.92^b,x	2.94^b,y	<2.0	6.19^ab,x	<2.0	<2.0
	5	6.83^ab,x	2.98^bc,y	<2.0	6.74^c,x	2.70^cd,y	<2.0	6.10^b,x	<2.0	<2.0
	21	6.74^abc,x	2.12^e,y	<2.0	6.93^ab,x	2.09^e,y	<2.0	6.13^b,x	<2.0	<2.0
14	0	6.89^a,x	3.32^a,y	<2.0	7.09^a,x	3.20^a,y	<2.0	6.58^a,x	<2.0	<2.0
	5	6.64^bcd,x	2.77^c,y	<2.0	6.89^bc,x	3.24^a,y	<2.0	6.50^ab,x	<2.0	<2.0
	21	6.86^a,x	2.47^d,y	<2.0	7.06^ab,x	2.89^bc,y	<2.0	6.50^ab,x	<2.0	<2.0

Values with different superscript letters (a–d) 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.