Biomedical Engineering Reference
In-Depth Information
only resulted in off-flavor development but also contributed to color deterioration.
44
By decreasing the dose to 1.2 kGy the sensory problems were eliminated and the
mold-free shelf life was extended 12 to 15 days when stored at room temperature. In
contrast, non-irradiated cheese became moldy within 3 to 5 days. When combined
with refrigeration storage, radiation increased the shelf-life period of the cheese five-
fold. With Gouda cheese, however, no taste difference was reported between irradiated
(3.3 kGy) and non-irradiated samples.
45
Similar taste findings were reported in a study
that evaluated the acceptability of irradiation sterilized dairy foods for immunosup-
pressed patients.
46
In this study, a Gouda-based process cheese was initially frozen to
-78°C and then gamma irradiated at 40 kGy. Although mozzarella cheese was similarly
treated, the result of sensory evaluation was far less favorable. Interestingly, both
cheeses maintained their characteristic mouth-feel properties despite being frozen. In
addition, the relatively high treatment dose resulted in only slight color changes. It
should be pointed out that while higher doses are required for sterilization purposes,
the product once treated has an indefinite shelf life from a microbiological standpoint,
provided of course that sterility is maintained. For Camembert cheese, flavor changes
described as burnt or musty first became noticeable when treated with 0.30 kGy.
47
In
order to stabilize the cheese by preventing additional growth of
Penicillium roquefort
i,
a minimal dose of 2.0 kGy was recommended. Results from a subsequent study,
however, reported that full fat Camembert cheese suffered no off-flavor development
up to a dose of 3 kGy;
48,49
and that treatment at 2.5 kGy was sufficient to eliminate
initial populations of 10
3
to 10
4
colony forming units (cfu)/g of the pathogen
Listeria
monocytogenes
.
50
In contrast, flavor changes were quite noticeable when radiation
treatment was applied to cottage cheese, the minimal threshold dose being 0.75 kGy.
47
At this dosage the cheese was described as having a slight bitter, cooked, or foreign
taste. However, in order to reduce spoilage by psychrotrophic bacteria by at least three
logs, the applied dose would have to be nearly doubled.
47
This resulted in cheese with
a definite burnt off-flavor. Using electron beam irradiation and doses of 0.21 and
0.52 kGy, the shelf life of vacuum packaged cheddar cheese at 10°C containing
10
1
cfu cm
-2
Aspergillus ochraceus
spores was extended by approximately 42 and
52 days, respectively.
51
Under similar conditions, inoculation of cheese with
Penicil-
lium cyclopium
spores resulted in shelf-life extensions of only 3 and 5.5 days, respec-
tively. Overall, the efficacy of the treatments was shown to be heavily reliant on the
irradiation resistance of the target microorganisms and the temperature of storage.
Increasing the post-irradiation storage temperature from 10 to 15°C, for example,
decreased the extension in shelf life. Although these results are to be expected, based
on the mesophilic nature of the target fungi, the increase in temperature may also have
contributed to more efficient repair of injury by the survivors.
Other Dairy Products
Sterilization of yogurt bars, ice cream, and nonfat dry milk by gamma irradiation
using a dose of 40 kGy at -78°C resulted in an overall decrease in acceptance.
47
Although the use of MAP or the inclusion of antioxidants appeared to reduce the
level of off-flavors, the effects were product specific. Irradiation of fluid milk also
resulted in unacceptable flavor scores.
52
Off-flavors and browning originating from
Search WWH ::
Custom Search