Here is a direct link to a PDF file (does not take too long to load) at the
Canada Flax Council's site about flax heat stability;

http://www.flaxcouncil.ca/pdf/stor.pdf

"Alpha-linolenic acid
ALA, in isolated form or as a component of an
extracted purified oil, is generally considered
susceptible to oxidation 3 because it is highly
unsaturated; that is, it has three double bonds in its
18-carbon chain. Oxidation is encouraged by both
warmth (autoxidation) and light (photo-oxidation)4 .
However, ALA in the intact seed of flax has proven
remarkably resistant to oxidation despite the fact that it
makes up about 50-59% of the oil in flaxseed which in
turn is normally 35-45% of the seed weight 3 . Why this
is so remains a question but the facts are clear, as
represented by current research.

Storage effects:

Flaxseed, either whole or coarsely ground, appears
stable to long-term storage at room temperature. Even
after 308 days at 22°C (72°F) there was essentially no
change in peroxide value as a measure of oxidation
by-products or in the percentage of ALA in fat extracted
from the stored flaxseed samples 5 . This demonstration
of oxidative stability in common storage was later
confirmed by direct measurement of oxygen [...]

Baking effects:

ALA in whole and milled flaxseed also appears to
be stable to heat equal or greater than the
temperatures involved in baking batters and doughs
such as muffins and yeast bread. Thermal stability was
shown in 1992 by the absence of significant changes in
peroxide values and fatty acid composition when both
forms of flaxseed were heated for 60 minutes at either
100°C (212°F) or 350°C (662°F). Furthermore, gas
liquid chromatography showed no signs of new trans
isomers of ALA or of cyclic fatty acid formation in
samples subjected to these degrees of heat 5 . In a
follow-up study the proportion of ALA in the fat of a
muffin mix, where 28.5% of the formula was milled
flaxseed, was virtually unchanged after baking at 178°C
(350°F) for 2h (45.1% ALA before:45.0% after). This
stability was observed even though oxygen
consumption of the flaxseed muffin mix was
considerably greater than that of the control muffin
mix 6 . A subsequent study confirmed the stability of
ALA in baked muffins containing the same amount of
milled flaxseed and noted that thiobarbituric acid
values, as estimates of ALA oxidation were also
unaffected by baking 9 ."


Marilyn