RE: Re[2]: Food irradiation

[keith.millington@tft.csiro.au]

M james wrote:
 
>     For heaven's sake!!  Free radicals only last <1 
> millisecond.  Not even my 
>     kids could eat the irradiated food that fast.  Lets get serious.

There seems to be a widespread perception that all free radicals are short
lived. This is not true. Polymer scientists know that many free radicals in
polymers are highly persistent, often having lifetimes of several weeks /
months or even years. Lifetimes of free radicals are clearly correlated with
their mobility - if they are small (like OH) they can easily and rapidly
annihilate each other or react with other nearby molecules. In
macromolecules or biopolymers this may not be so straightforward,
particularly in the absence of a tranfer medium such as water. I note that
meat is mainly fibrous long-chain protein (collagen) and fat.
I have no experience in food irradiation, but I would imagine that much R&D
has been done to look for free radicals in irradiated foodstuffs with esr. I
would be very interested to hear the results of such studies, particularly
on dried meats, dried processed foods for rehydration or foods containing
high levels of sulphur-containing organics such as the amino acid cystine,
which (in my experience on wool) may stabilise long lived radical species. 
Some of my current work is concerned with textile free radical chemistry,
and I have done some recent work looking at the use of 60Co irradiation to
sterilise raw wool in order to kill bugs, weed seeds etc that may cause
ecological problems when wool is exported overseas for processing. Wool is
also a fibrous protein (mainly alpha-keratin) and it demonstrates highly
persistent free radicals (by esr) after exposure to UV or gamma rays when
exposed under relatively dry conditions.
Another potential problem with gamma treatment of biopolymers which we have
observed is colour change. We exposed wool fabric to various doses of  60Co
gamma, and found that clearly visible colour changes occurred, even at a
dose of  50 kGy recommended for sterilisation by Australian quarantine
regulations. The wool colour changed from pale cream to pink / red. Also
this colour change was difficult to correct by subsequent peroxide
bleaching, which unfortunately meant that the wool would be devalued if
sterilised by irradiation. 
The radiation chemistry involved in the colour change of wool is highly
complex, but does have some similarities to the formation of melanins in
UV-exposed skin. I would be most interested to hear from other workers who
are looking at similar systems.
A paper on this has been submitted to J Soc Dyers and Colorists and should
appear later this year. A brief abstract has already appeared in Proc 23rd
Australian Polymer Symposium, Geelong,  1999, paper Q3/2, if anyone is
interested.
My views not my employers.
regards, Keith

Dr Keith R Millington,
Project Leader, Textile Photochemistry,
CSIRO Textile and Fibre Technology,
PO Box 21, Belmont, VIC 3216.
AUSTRALIA.
ph: 0352-464792
fax: 0352-464057
************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html