Does irradiation affect quality?
It is well recognised that irradiation can destroy bacteria and other micro-organisms in food – depending upon the dose. This processing / preservation method is controversial with many in the public being strongly against it. It is however the preferred method for preservation in some specific food types due to the nature of those foods. Herbs and spices are one of the food types that are often irradiated to reduce the mould load. Soft fruits, like strawberries, are also excellent candidates for irradiation.
We know about the effects on micro-organisms, but to determine if this is a method for use on a large scale commercially, we also need to know if there is any impact on quality characteristics of the foods being treated.
A recent study on ScienceDirect.com has shown that at higher doses, irradiation may have detrimental effects on flavours.
Cooked, ready to eat chicken breast was vacuum packed and then irradiated at either 5 kGy or 40kGy. Microbial tests were then done to determine the bacterial levels at the start of the study and no irradiation (the control) had a count of 4.75 colony forming units per gram (CFU/g) and the 5kGy samples were at 2.26CFU/g. There were no viable cells found in the 40kGy samples.
At 10 days into the study, the levels of bacteria in the control and 5kGy samples had increased and there were still none present in the 40kGy samples. This confirms that higher level of irradiation does give good preservation for long term storage.
The pH level of the food was found to be higher at the start of the study in the 40kGy samples but at that point there did not appear to be any change in the sensory scores for any of the samples.
On the tenth day, there was a sensory score difference with the 40kGy samples showing a higher score for off-flavours. When tested, these samples were found to contain hexane, heptane, pentanal, dimethly disulfide, heptanal, and nonanal – not found in either the 5kGy sample or control. There were also specific compounds found in the 5kGy samples that were not present in the control.
This study indicates that even though higher dose irradiation will have the desired reduction in bacterial levels, it may also cause a development of off flavours. Obviously more work needs to be done on other foods and doses, to find the irradiation dosage where optimum bacterial effect is achieved whilst minimising quality impact.
The study can be found at http://www.sciencedirect.com/science/article/pii/S0969806X11003732
Effect of high-dose irradiation on quality characteristics of ready-to-eat chicken breast
Hyejeong Yuna, Kyung Haeng Leeb, Hyun Jung Leea, Ju Woon Leec, Dong Uk Ahnd, Cheorun Joa.