Irradiation - Food Shelf Life Stability: Chemical, Biochemical, and Microbiological Changes - page 102

TABLE 3.3
Growth of Microorganisms (log 10 cfu/g) on Beef
Top Round at 1°C Following Radiation Treatment
at 2 kGy

Storage time (d)

Microorganism 0 3 7 10 21

Psychrotrophs: T a 1.66 — c — 3.11 6.16

C b 3.45 4.4

0

6.0
6

6.55 —

Mesophiles: T <1.58 — — 2.66 3.13

C 2.84 3.6

7

6.1
1

4.98 —

Pseudomonads: T <1.58 — — <1.58 <1.58

C 2.54 4.1

9

5.4
9

6.38 —

a Treated
b Control
c Not performed

Adapted from Rodriguez et al. 157

product spoilage. A sensory panel determined that the radiated samples were superior
in both appearance and odor throughout the storage period when compared to the
controls. Decreasing the treatment temperature from 25 to 0 to 2°C was also rec-
ommended as a means of minimizing sensory changes. The shelf life of top round
beef cuts packaged in polyethylene wrap was similarly extended following treatment
with 2 kGy. 157 Based on psychrotrophic bacterial counts ( Table 3.3 ) and using a
cutoff value of 10 7 cfu/cm 2 , which coincided with undesirable sensory changes,
product shelf life at 1°C was extended an additional 17 days compared to controls.
At 8 to 10 days of storage, both odor and color had deteriorated in the controls;
however, treatment samples even after 4 weeks maintained an overall acceptability
score of 7.5, with 10 being the highest. As shown in previous studies, a pronounced
reduction in spoilage bacteria including Pseudomonas and Brochothrix thermo-
sphacta was achieved during treatment. 156

Ground or Comminuted Beef and Pork

Freshly ground or comminuted beef also has a relatively short shelf life, typically
from 4 to 7 days, even when maintained under proper refrigeration temperature. 158
Various factors contribute to shorten the shelf life; however, a large surface-to-mass
ratio and high initial numbers of spoilage bacteria in the range of 10 5 to 10 6 cfu/g,
which originate from trimmings and/or resulting from process contamination, are
mainly responsible. 159-161 Principally, Pseudomonas , Enterobacteriaceae , and lactic
acid bacteria are isolated. 161 Although Pseudomonas is easily eliminated, lactic acid