Irradiation - Food Shelf Life Stability: Chemical, Biochemical, and Microbiological Changes - page 93

Synergy involving chemical pretreatment of carcasses and radiation has also
been examined as a means of extending shelf life. In one such study, carcasses were
dipped in either fermented whey (thermophilus whey) or a 1% lactic acid solution
and radiated with 2.5 kGy at 3°C. 61 Although the numbers of Gram negative bacteria,
Yersinia and Campylobacter in this study, were significantly lower in radiated vs.
non-irradiated samples, no differences were observed among the pretreatments,
which included water dipping as a control. However, the proportion of salmonellae-
positive contaminated carcasses did decrease from 67 to 20% as a result of whey
pretreatment. Overall, using Gram negative plate counts of 100 million per carcass
as an index of spoilage, the shelf life of the controls was extended an additional
9 days as a result of radiation treatment.
Further Processed Products
Using canned minced chicken meat Thornley 93 reported that storage life could be
extended from 1 to at least 4 weeks following treatment with 2.5 kGy. From a sensory
point of view, however, the product appeared pinkish and transparent and was
accompanied by a distinct odor that was not attributed to microbial growth but rather
to the treatment itself. However, following cooking the taste panel found it difficult
to distinguish the treatment sample from the control. How the product is cooked
following radiation treatment may therefore have an influence on whether or not
odors are detected. For instance, in several studies experienced taste panelists could
not detect radiation odors on roasted chicken which had been previously treated at
7 to 8 kGy; 98,99 however, when chicken was radiated at a lower dose of 1.25 to 5 kGy
and steam-cooked, the taste panel could readily identify off odors. 89 Pinking and or
the development of a red color was also reported following treatment with 1.25 to
8.0 kGy of whole eviscerated chicken and turkey during refrigerated storage. 89,98
The mechanism for its appearance is unknown but presumably is non-microbial.
Irradiation of fresh or frozen tray-packed, cut-up fryer chicken shortly after process-
ing using a dose of 5 kGy significantly delayed growth of spoilage bacteria during
storage at 4.4°C for 21 days; however, objectionable off-odors were still detected
2 to 4 days post-irradiation. 100 Decreasing the dose to 1 kGy eliminated odors but
did little in extending the shelf life of the product. An intermediate dose of 3 kGy
was finally recommended for shelf life extension since off-odor development was
minimal within the 14 days of storage; overall a 21-day shelf life was achieved.
Chicken breasts irradiated using cobalt-60 at a dose of 2.5 kGy and stored at 2°C
resulted in a two log reduction in aerobic bacteria counts. A level of 10 6 cfu/g, which
coincided with initial signs of spoilage, was reached 19 days post-slaughter. 69 Com-
bined with refrigeration, the gamma treatment was shown to extend the shelf life of
the samples by at least twofold over the controls. At this dosage off-flavors and
odors were not detected by a trained sensory panel for up to 22 days of storage;
higher treatment doses resulted in lower flavor and acceptability scores. In addition,
the panel reported that tenderness was significantly lower in the radiated samples.
The increased firmness of the treated samples was correlated to reduced water
holding capacity and increasing the treatment dose from 3.5 to 4.5 kGy further
decreased the water holding capacity of the samples from about 72 to 68%, respectively.