Irradiation - Food Shelf Life Stability: Chemical, Biochemical, and Microbiological Changes - page 90

chemical reactions involving lactose were identified. 52 Irradiation preservation of
yogurt was similarly investigated. 44 Left at room temperature, plain yogurt reached
a population of 10 9 cfu/g by 6 days and was judged unacceptable; however, when
treated with gamma irradiation using a dose of 1 kGy this population level was not
reached until 18 days of incubation. Irradiation combined with refrigeration further
extended the shelf life of yogurt to 29 to 30 days. In comparison, the shelf life of
the refrigerated controls was only 15 days.
P OULTRY
Chicken and Turkey
Radiation treatment of poultry products as low as 1 kGy is currently allowed in
several countries. In the U.S., fresh or frozen poultry and further processed poultry
products including mechanically separated meat can be radiated to an absorbed dose
between 1.5 and 3 kGy. 53,54 If the products are intended for packaging, the film must
be permeable to oxygen in order to reduce possible growth and subsequent toxin
production by Clostridium botulinum . In the Netherlands the maximum dose
approved for poultry is 3 kGy, while in Israel and South Africa treatment doses as
high as 7 kGy may be used. 55 The latter dose is sufficiently high to eliminate
salmonellae in fresh poultry; however, flavor problems invariably arise. 55 Threshold
doses of 2.5 and 1.5 kGy have been reported for chicken and turkey, respectively,
following radiation at temperatures of 5 to 10°C in plastic bags. 9,56,57 For this reason,
doses higher than 2.5 kGy are normally reserved for application to frozen poultry
products since reduced available moisture is known to render microorganisms more
radiation resistant and interaction of free radicals generated during treatment with
food components is largely constrained. 11,58,59
At or below these dosages, however, there is no guarantee of producing salmo-
nellae-free carcasses. 60 Despite this lack of assurance, a 2-kGy dosage should be
sufficient to adequately reduce or even eliminate salmonellae in poultry provided
that production and processing was performed under good production and manufac-
turing practices. 55 Indeed studies have provided data to suggest that treatment at this
dose not only eliminates salmonellae from chicken wings and mechanically deboned
chicken meat 61 but also reduces the initial microflora on whole carcasses by 99%. 62,63
At a dose higher than 2.5 kGy, over 99.9% of the initial aerobic plate count can be
destroyed. 64 Radiation treatment of poultry is currently not allowed in Canada or
Great Britain. An expanded list of countries that currently allow radiation treatment
for poultry and poultry products is given by Farkas. 9
Under normal processing conditions freshly eviscerated and chilled whole
chicken carcasses will have a shelf life that is dependent primarily on both the
microbial load, principally Pseudomonas levels, and the storage temperature which
typically ranges from 2 to 4°C. Although the numbers and types of psychrophilic
microorganisms found on carcasses immediately after processing varies, they are
usually less than 10 4 cfu/cm 2 and may be as low as 10 2 cfu/cm 2 . 47,65 When the
population of spoilage microorganisms on polyester tray or polyethylene bag-pack-
aged carcasses reaches levels of about 10 7 to 10 8 cfu/cm 2 , unpleasant off-odors,