RE: Re[2]: Food irradiation

["Neil, David M" <neildm@id.doe.gov>]

Comments interspersed

On Monday, April 03, 2000 6:59 PM, keith.millington@tft.csiro.au
[SMTP:keith.millington@tft.csiro.au] wrote:
> 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.
Tissue (meat) is mostly water.  Even adipose tissue (fat) and cartilage
(collagen) are mostly water.  I don't have the figures ready to hand, but
memory is that it's 70 -90%

> 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 

Water, again.  If free radicals persist, immobilized, in dry food, and
disappear on hydration, long (relative to the reaction speed) before it
reaches your fork, what difference does it make.  And dried meats still
contain more water than it seems. Even highly desiccated meat has to be
partially hydrated in consumption, or you can't even chew it.

>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.

No knowledge, so no comment.

> 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. 
A very valid point in its own context, but relative to food irradiation
we're not comparing apples and oranges, we're comparing apples and (orange)
sweaters. (Sorry, I can't resist a straight line like that)

> 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.
I am interested enough to take a look, but I expect both will be somewhat
difficult to locate for me.  Will there be any Web publication?

Dave Neil		neildm@id.doe.gov

Werner Heisenberg: We are not sure which side of the road the chicken was
on, but it was moving very fast.

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