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Does heat or processing denature proteins in a harmful way?

Answered on May 09, 2014
Created May 08, 2014 at 4:50 PM

I've often heard by raw food advocates, those against microwaves and those against processed foods that heat and processing will denature proteins in a harmful way. Researching myself, it seems that proteins are chains of amino acids folded in certain ways. Heat, pressure, changes in PH, and digestion (a change in PH) often causes the proteins to change their fold pattern. Sometimes the new fold pattern is easier to digest and sometimes it's harder to digest. If it was an enzyme, it will no longer be bioactive if the form is changed. On the surface of it, if the complex protein is broken down into it's constituent amino acids, then one might wonder if it matters how that happens whether by heat or by digestion. But apparently, heat, pressure and changes in PH don't just break down proteins into constituent aminos, they can also change the amino acids' forms (racemization) and result in cross linking of amino acids in new ways.

http://pubs.acs.org/doi/abs/10.1021/jf00126a040?journalCode=jafcau .

Amino acids can have two different configurations, "D" or "L" which are mirror images of each other. With a few important exceptions, living organisms keep all their amino acids in the "L" configuration but processing can convert many aminos to the "D" formation (D formation aminos are also suspected of being the problem with manmade MSG)

In the case of crosslinking, the crosslinked aminos in their new form may become totally indigestible or even toxic. This seems to happen more in presence of sugars. For instance, certain amino acids when heated with certain sugars create acrylamide, a known cancer causing agent common in processed foods that has been in the news a lot recently. Looks like different proteins are susceptible at different heat/temp/PH gradients. Research suggests quite an extensive drop in digestibility for animal feeds that get more heat processing but many methods of food processing, like extrusion, and the way white rice is heat/pressure treated to prevent germination, create both very high heat and very high pressure and the food industry is promoting these foods as supposedly healthy.

How much should we worry about heat treatment altering amino acids and how much will be dependent on the extent of the processing? (good data sources much appreciated)

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on May 09, 2014
at 06:35 AM

Here is an interesting Soybean meal fed to pigs undergoes heat treatment to destroy trypsin inhibitors and other ant nutritional factors that impair the digestion of protein and thus reduce performance.

1. Soybean meal Autoclaving at125°C for 15 min reduces digestibility of aspartic acid and lysine but had no effect in digestibility of any other amino acid.

2. Where Soybean meal Autoclaving at125°C for 30 minutes do reduced the digestibility of all amino acids.

3. Amino acids do not get damaged by over drying soybean meal. Moisture is required for reaction to take place.

4. For analyzing heat damage in sample of soybean meal requires comparison of lysine to crude protein ratio.

You can get more related study by searching for Hans H. Stein.

Hope this might help you.

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