mudpuppy
Posted : 1/22/2009 11:30:26 AM
There's only a few nutrients that are de-natured by cooking. Some are changed but not "lost" necessarily.
where you do get this idea? it's untrue. Many vitamins are heat-labile and are destroyed by regular cooking times, and totally gone after a 24+ crockpot experience. Quote from Proceedings of the Nutrition Society, UK about loss of vitamins from meat during normal cooking times:
"Meat is an important source of certain vitamins of the B group.
Fortunately most of these substances are moderately heat stable and so,
though losses occur by the same mechanism as that which brings about
losses of water soluble salts, actual destruction is not very great, and a
considerable part of the “lost” vitamins can be found in the drippings.
It seems to be fairly generally agreed (e.g., McIntire, Schweigert and
Elvehjem, 1943; McIntire, Schweigert, Henderson and Elvehjem, 1943;
Cover, McLaren and Pearson, 1944) that the loss of vitamin B, from beef,
veal, pork or cured ham, ranges from 20 to 50 per cent. according to the
method and duration of cooking, with a net destruction of about 20 to
25 per cent. With an average daily intake of 1OOg. of meat and an
average vitamin B, content of 100 I.U. per 100 g. raw meat there
would be a maximum daily cooking loss of about 50 I.U. of vitamin
B,; this could only be serious if, owing to the exclusive use of low
extraction cereals, meat were promoted from a minor to a major source of
vitamin B,.
The better known members of the vitamin B, complex are more resistantto heat than vitamin B,; the losses of these substances appear,
as would be expected, to be smaller. Thus, according to the workers
quoted for vitamin B, losses, the loss of riboflavin ranges from 15 to
25 per cent. (0 to 13 per cent. if the drippinga are included); that of
nicotinic acid fiom 15 to 35 per cent. (0 to 10 per cent. including the
drippings) and of pantothenic acid from 10 to 25 per cent. Accordingto Schweigert, Nielsen, McIntire and Elvehjem (1943), 80 per cent. of
the biotin of meat survives cooking. "
Loss of vitamins from potatoes cooked for normal period of time:
"Vitamin B, and ascorbic acid are
both subject to destruction, t.he former being heat labile especially at
high pH, the latter subject to oxidation catalysed by copper and by
certain enzymes, this also bcing more rapid at pH above 6. Accordingly,
the losses are greater if cooking is slow, and especially by the initial
raising of the temperature before enzymes have been destroyed (Allen
and Mapson, 1944). The destruction of ascorbic acid and vitamin B,
appears to continue after cooking is complete and the vegetables, exposed
to air, await serving. Thus Nagel and Harris (1943) found that in large
scale cooking, potatoes lost 35 per cent. of their vitamin 13, and 45 pcr
cent. of their ascorbic acid; after standing on the hot plate these losses
were increased to 70 and 75 per cent'., respectively. Similarly, Kahn
and Halliday (1944) found that, although potatoes steamed in their skins
lost little or 110 ascorbic acid even after 50 minutes on the hot plate,
baked potatoes lost 20 per cent. of their ascorbic acid during cooking
and a further 39 per cent. after 43 minutes on the hot plate, while steamed
potatoes whicH had lost 39 per cent. during cooking lost ncarly all the
remainder when mashed and allowed to stand (cf. Esselen et al., 1942)."
grains:
"
It seems that, as one would expect from
the known behaviour of pure vitamin B,, the loss in cereal cooking isminimized by preserving as low a pH as possible and by avoiding excessive
heating. This probably applies also to certain members of the
vitamin B, complex, the stability of which resembles that of vitamin B,."