Carol:
> It stands for Unique Radiolytic Products.  They are often mentioned
> in discussions of food irradiation, not as much in those of microwave
> ovens, but the connection has been made by some.  I'm not very educa-
> ted about them myself, but what I have read I've found interesting.
> I don't have references for the non-internet articles I've read about
> them, but there is a little overview of some of the objections to
> microwave ovens at http://www.icom.net/~nexus/microwave.html, and in
> that article, the term "radiolytic compounds" is used.  That term may
> be used interchangeably with "URPs" by some people; I don't know.

I've heard the term "radiolytic" before. "Radiolytic compounds" are
molecules created by microwaving/irradiation; I suppose that URPs are
those radiolytic compounds that occur neither naturally nor with
ordinary cooking. The few remarks about URPs that come to my mind are:

1. In some sense, irradiation is much more "violent" than
microwaving. Gamma photons (used for irradiation) can extract
electrons from their orbits (even electrons from inner "layers"),
thereby creating free radicals. The latter can then recombine, leading
to the formation of URPs. If irradiation occurs in the presence of
water, some oxygen peroxide (H2O2) is formed, which can in turn react
with other substances. On the other hand, photons in microwaves are
about 10 billion times less energetic, hence cannot extract electrons
from atoms. Most of the energy from microwaves is absorbed by
water. Water is merely heated, is not affected in any other way, and
in
turn heats nearby molecules by conduction: thus there is nothing more
here than with ordinary cooking. However, fats and sugars also absorb
a little energy from microwaves, and are "shaken" in a different way
than with "normal" cooking: this may be (I think) the reason why new
molecules may appear (if they do).

2. I am not aware of any proof that microwaving produces URPs (in the
sense given above).

3. Assuming microwaved foods do contain URPs, it should be recalled
that cooked (e.g. boiled, steamed) foods contain countless molecules
species that don't occur in raw foods (MRPs: Maillard Reaction
Products). I fail to see why one should be more afraid of URPs than of
MRPs.

4. There is no evidence that any URP in irradiated foods (or
hypothetical
URPs in microwaved foods) is carcinogenic. No scientific study has
shown any carcinogenic effect of irradiated or microwaved foods.
None of the known mutagens or carcinogens formed in meat cooked at
high temperature is formed in microwaved foods. On the contrary, it
has been shown that microwave pretreatment of beef patties before
frying reduced mutagenic activity (compared to beef fried without
pretreatment).

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