Ask A Scientist General Science Archive

name         Martha
age          50s

Question -   An elderly friend heard that microwaving has an
especially destructive effect on the enzymes in food, and as he knows the
nutritional value of enzymes, he has stopped using his microwave until he
can learn more. I believe that heat destroys enzymes, but is there
something in microwaves that also does so? What can I tell him about
protecting the beneficial aspects of enzymes while preparing food?
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Heat, of any sort above about 50 degrees C pretty much destroys any of the
enzymatic activity in most foods.  This will occur when one either cooks by
microwave of normal oven, simmering, frying etc.

Peter Faletra Ph.D.
Assistant Director
Science Education
Office of Science
Department of Energy
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Enzymes IN food can help digest some types of foods.  Examples include
lactase supplements for lactose-intolerant people and alpha-galactosidase
(Beano) for help digesting those beans and such.  Enzymes themselves do not
have much nutritional value beyond that of any other protein, though.  Most
ingested enzymes are broken down in the gut just like other proteins.

The way microwaves affect food is through the heat they create when they are
absorbed.  In other words, microwaving food denatures food enzymes because
it heats them.  There is nothing special about the microwave;  it is just a
convenient way to heat food quickly.  If you want to preserve enzyme
activity in food, do not heat it.

This is the reason that jello will not set if you put fresh pineapple, 
kiwi, or
papaya in it.  The protein-degrading enzymes in those fresh fruits break
down the gelatin.Cooking the fruits first (such as when they are canned)
destroys this effect.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois
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Martha,

There is nothing special about destruction of enzymes by microwaves.  Home
appliance microwaves simply heat water in the food. It is that heat which
cooks the food -- and destroys the enzymes.

However, you should note that enzymes are proteins (complex chains of amino
acids)  -- and proteins are digestible. No enzyme taken orally can survive a
trip through the hostile digestive juices in the intestines. If eaten,
enzymes are digested just like any other protein. Once digestively degraded
into its constituent amino acids, the enzyme has no catalytic properties.
Other than the very slight nutritional benefit which might be derived from
an orally ingested enzyme -- because it is a protein -- there is no
substance to the notion of "nutritional or beneficial value of enzymes."
Products that allegedly contain enzymes intended to be taken orally are a
dishonest scam.

Indeed, the body uses many kinds of enzymes to carry out the multitude of
chemical reactions necessary to sustain life. Rather than deriving these
enzymes from food (or pills) the body synthesizes those it needs from the
materials in the diet.

Surely, one should consider the fate of heat-sensitive vitamins when
preparing food. However, vitamins and enzymes are not the same thing. Those
who spend their hard-earned funds on enzyme preparations -- be they from
food, tablets, or elixirs -- are wasting their money.

Regards,
ProfHoff 404
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In general, microwaves do not effect proteins, enzymes, or most other large 
molecules any differently than heating in a conventional oven or 
boiling.  The microwaves are absorbed primarily by the water molecules in 
the food.  Heating of the water then heats the rest of the food indirectly.

That said, it is certainly true that boiling, either in a microwave oven or 
on a stovetop, is a very effective means for "denaturing", or unfolding, 
proteins and enzymes, which usually also inactivates the enzymes.  However, 
most enzymes in foods are inactivated by the digestive enzymes and acid in 
the stomach anyway, converting them into their constituent amino 
acids.  The amino acids
are not effected by denaturing and are really the most important 
nutritional component of proteins and enzymes, not the activity of the 
enzymes.  Because of this powerful digestive process, most 
enzyme-containing products promoted by various nutritional supplement 
companies are of dubious health benefit, other than as an amino acid source.

Thank you for the good question, which was probably a bit more complex than 
you might have expected,

Jeff Buzby, Ph.D.
=========================================================
The vast majority of enzymes can be considered to be a special class of
proteins. Their nutritional value is the same as any other proteins, no more,
no less. They are called enzymes as a group because of the way they function
in the cell that they normally exist in. When you digest enzymes, whether
they are raw, baked, microwaved, or boiled, you break them down so that
whatever function they USED to do is no longer going to happen. Period.

When you eat enzymes or any other type of protein, your body digests them
down to their building blocks, which are amino acids. Cooking proteins
changes their "shape," which can affect their structure, but not necessarily
their nutritional value. For an example of this, just think of the way the
protein in egg white appears different when raw versus cooked. The cooked egg
white protein has a different structure, which causes it to coagulate, while
the raw egg white does not.

To say that heat destroys enzymes is just to say that it changes their shape
so that they cannot do what they normally do *in the cell they came from*.
But since this function is not going to be happening in your body after you
digest the enzyme, it does not matter whether the enzyme was cooked or not.
It's nutritional value is the same.

Paul Mahoney, PhD
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