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Ron Peterson

wrote:
> Ron Peterson wrote:

> > If the oil isn't reused, it can be expensive. And, if it is reused,
> > unhealthy byproducts can build up in the oil.

> What kind of unhealthy byproducts? Do you have any references we can
> see regarding the claim? I tend to reuse about 3-4 times before
> ditching it; I filter before putting it into my refrigerator in an
> air-tight container.

A google search revealed the following:
"In the present investigation, high resolution nuclear magnetic
resonance (NMR) proton and carbon spectra were used to non-invasively
measure the degradation of frying oil caused by heating. Fresh and aged
canola oil samples were analyzed by NMR proton and carbon spectra.
Canola oil was heated to 180 °C while exposing to (1)air and (2) air
and water steam and stirred constantly. The NMR proton spectrum showed
that no aldehydes (n-alkanals and branched alkenals) were presented in
fresh canola oil, but they appeared after 4 hours of heating. They
reached a maximum (1.35%) after 24 hours in air degraded oil and
reached a maximum (1.45%) after 36 hours in air and water steam
degraded oil. Aldehydes are of concern because they exert a range of
negative toxicological effects. The carbon spectrum of fresh canola oil
is mainly triacylglycerides. However, in canola oil that was heated for
4 hours two noticeable changes occurred. First, oxidation increased oil
saturation level with selectivity towards n-3 double bonds and these
reduced fatty acids were then converted into aldehydes. Second,
triacylglycerides were broken down into free fatty acids and mono- and
di-acylglycerides via hydrolysis. Canola oil heated while exposed to
air degraded faster than exposed to air and water steam. These results
illustrate the capability of NMR to noninvasively quantify oil
degradation and the by-products formed during the frying process."

--
Ron