List at least six factors that denature proteins:

(1) Temperature Change [usually higher, but also lower]

(2) Mechanical Actions [whipping, shaking beating]

(3) Irradiation

(4) Chemical Methods

(5) Pressure

(6) pH changes [usually lower, but also higher]


State the functions of protein in food production.

Gelling Agent

Texturizer

Emulsifier

Foaming Agent

Dough Formation

--Ms.Spector, Food Science & Technology http://www.hshm.us/SPECTOR.htm 

How does acid denature the protein in egg white? How does beating of egg
white denature proteins?

When the three-dimensional arrangement of the helical structure of the
polypeptide chain is altered, a protein molecule is said to be "denatured".

When the bonds that maintain the unique spatial arrangement of the protein
molecule are disrupted, it is free to unfold or extend. These bonds may be
disrupted in a number of ways. Heating a protein that is dispersed in water
may break hydrogen bonds, as may a high concentration of salt. Protein
molecules whose conformation is stabilised by salt bridges are sensitive to
changes in acidity.

Certain protein molecules can be denatured by spreading them in thin films
as in a foam. Mechanical action during the whisking of egg white causes a
partial coagulation of the protein. The protein molecules unfold and form a
reinforcing network round the air bubbles, thus stabilising the foam.

--Singapore Science Center http://www.science.edu.sg/ssc

But besides acids and heat, a variety of other kinds of situations can
denature proteins. High concentrations of salts, including table salt
(sodium chloride) can do it. Air can do it, as happens in the bubbles formed
when cream is whipped. Even alkalis, the opposite of acids, and low
temperatures, the opposite of heat, can do it, but less commonly. The
cooking analogy comes only from the fact that heat is the most familiar
protein-denaturing agent in the kitchen.

Denaturing or unwinding protein molecules is no great trick, because the
bonds that keep them twisted and folded aren't very strong. Evolution may
supply a rationale for that fact: Over the eons, specific proteins have
evolved to do specific jobs in specific living organisms, so they have no
need to be stable under conditions vastly different from those that prevail
in the organisms they serve. Thus, meat and fish [and milk] proteins can be
destabilized when subjected to higher acidities and higher temperatures than
those in the animal's muscles [or body]. 

--The Acid Test, Robert L. Wolke
Wednesday, November 10, 2004; 
Washington Post, Page F01

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