Denatured Proteins in Cooked Foods: Is This Important?

Denatured Proteins in Cooked Foods: Is This Important?


Raw foodies, and those selling so-called raw
whey, make a big deal about proteins being denatured by cooking and they claim that this
causes food to loose its natural goodness. So what does it mean for a protein to be denatured?
Well, proteins are big molecules with a complex 3-dimensional shape. For a protein within
your body, this shape is integral to its function. So, they have it right when they say that
denaturing of a protein renders it “nonfunctional.” What you need to understand is that, for the
most part, digestion breaks down proteins into smaller sub-units: dipeptides, tripeptides,
and single amino acids. The first step in protein digestion is actually in the stomach.
The only thing that happens to proteins in the mouth is it’s crushed and broken up by
chewing, and moistened by saliva. The true digestion begins in the stomach, where hydrochloric
acid is released. Guess what this acid does? It denatures the proteins, meaning that it
begins to unfold them out of their 3-dimensional shape. This is very important because it helps
digestive enzymes gain better access to the protein bonds. During digestion in the stomach,
muscular action is churning the food contents around so that they can be better mixed with
the acid, resulting in more thorough denaturation! This results in a semi-fluid mixture called
chyme. The hydrochloric acid in the stomach also
triggers the release of pepsin. Pepsin is an enzyme begins to break some of the protein
bonds, resulting in polypeptides, which are long chains of amino acids, but still shorter
than they were to begin with. This process, in the stomach, accounts for about 10-20%
of the protein digestion. From there, protein digestion is continued
in the small intestine. The pancreas makes an alkaline juice which is released into the
small intestine to neutralize the acid, so that other enzymes can do their work. Protein
digesting enzymes called proteases, released by both the pancreas and the small intestine,
break down the chains of amino acids into even smaller chains. And, special cells in
the lining of the small intestine also release other enzymes called peptidases, and these
break the chains into little chains of two or three amino acids, called di- and tripeptides,
as well as some single amino acids. These dipeptides, tripeptides, and single aminos
are then absorbed by facilitated diffusion or active transport, which mostly occurs in
the cells that line the intestine. In these cells the final step occurs, and the protein
chains are broken down by other peptidases into individual amino acids. The intestinal cells themselves use some of
these amino acids, but most of them are transported, by facilitated diffusion, into the portal
blood vessels and go right to the liver which either uses them or releases them to the general
blood circulation. Although it is not unheard of for whole proteins to be absorbed, this
is extremely rare unless you are a fetus or a newborn infant. Protein digestion and absorption
by the body is very efficient and pretty much all of it is used. The little protein that
is not digested goes into the large intestine where it is excreted. So what can we say about this this cooked
and therefore “denatured” food? As you have learned, denaturing is an important part of
the digestive process. This unfolds the proteins and makes the protein bonds more accessible
by the enzymes, so that proteins can be efficiently broken down. When you cook a protein, you
denature it in a similar way to how the acid in your stomach does. In fact, professional
chefs know that you can basically “cook” a protein by applying an acid to it. Most proteins,
when they are heat treated and denatured in this way, become more available to the body
for digestion. For instance, when you cook egg whites, they turn white and solid. This
means they are denatured. The protein from cooked egg whites is actually more available
to the body and will be better absorbed uncooked egg white. The, ah, image appearing on your screen right
now, is a great illustration of this. It uses the simple analogy of paper clips as proteins.
Imagine that the proteins in the liquid egg whites are orderly and distinct like the paper
clips, and when they are denatured by heat these paper clips unfold and sort of get wound
up with each other. Now, imagine if you are an enzyme trying to digest these proteins.
When the paper clips are in their normal and functional configuration, much of their parts
are folded away and close together in such a way that it is difficult to access them.
Once they are denatured and opened up, as you can see from the picture, the stuff that
makes up the paper clip is easier to get to. This is a perfect analogy for protein denaturation
and digestion. Most enzymes, which are also proteins, that
are present in the food will also be denatured by the stomach’s acid and then broken down
like any other protein. These are enzymes that would normally require a more neutral
PH to function. In other words, they need a less acidic environment to work. Now, some
have made a big deal about certain plant enzymes being acid stable. However, they don’t bother
trying to prove in any way that these plant enzymes have a role in human physiology. As
I explained in the previous video about raw foods and enzymes, plant enzymes are for plants
to use, not for us. So I just told you that enzymes will tend
to be broken down in the stomach, and so they would cease to function. In order for an enzyme
to survive in the stomach and function, it must be acid stable. Remember how I said that
pepsin worked in the stomach, but then, when the stomach contents are released into the
small intestine the acid goes with them? If this acid was not dealt with, the small intestine
enzymes would not work because they require a less acidic environment. This is why the
pancreas releases an alkaline substance so that the pH is made more neutral. But you’ve
seen enzyme supplements for sale. So, is there a such thing as an enzyme, which is a protein,
that you can take and it will not be made nonfunctional in the acidic environment of
the stomach? Yes. Many lactose intolerant people successfully
take commercial preparations of lactase enzyme. This allows them to ingest varying quantities
of milk and dairy products. Now, humans are not the only organisms to produce lactase
enzymes. Other organisms do as well. For instance, some bacteria, such as E. coli, make such
an enzyme. And so do some yeasts. However, the optimal pH of the enzyme these organisms
produce is usually more alkaline than the low pH of the stomach. This means they like
a pH range of anywhere from 5 to 7, with 7 being more or less neutral. The pH in the
active stomach can be from 1 to 3. A preparation made from this lactase would not survive,
unless an effective enteric coating was used. This is how some lactase products work, with
enteric coatings. On the other hand, a very common solution is to use the lactase produced
by another organism, which is stable and active in acid. This organism is a fungus called Asperguillus
niger and a lactase enzyme can isolated from it which is active in a very wide range of
pH. Actually, this fungus makes a number of useful enzymes. It makes another enzyme called
Alpha-galactosidase, which helps to break down complex carbohydrates, and preparations
are made with this which can help decrease flatulence and other GI distress from eating
beans and other problematic starches. So yes, it is possible to consume an enzyme
and have it work in the stomach. But this does not mean that all the various enzymes
that plants contain will function in your body this way! The body has specific enzymes
that are used to digest the foods we eat. Some analogues, as seen, can be found elsewhere
in nature and used to produce products to help with maldigestion. These products are
purposefully and specifically prepared. They do not happen by accident and they are not
ubiquitous.