Молекулярная гастрономия для креативных шеф-поваров (англ. язык) - страница 230

Молекулярная гастрономия для креативных шеф-поваров (англ. язык)

are not reversible).

I - 5 (of 17)

Figure 5. A model of egg white coagulation. Many proteins of egg whites are coiled, because

the inner part is hydrophobic; being dissolved in water (egg white contains 90% water), the

proteins coil spontaneously, so that hydrophilic parts are in water, as hydrophobic parts are

buried. When heated, the energy of movement of the molecules induces an uncoiling of

proteins (“denaturation”) and, subsequently, a coagulation of egg whites, due to chemical links

between uncoiled proteins (bottom). Of course, such description is simplified, as, in particular,

proteins do not extend like threads.

How much does this theory hold? An experimental check is to ask the question: why are proteins

coiled? The answer is: because they are in water. Therefore in something else than water, they

should coil differently and perhaps coagulate also.

Let’s make the experiment of adding ethanol to an egg white: when the ethanol concentration is

enough, egg white coagulates. Of course, this can be done with something else than ethanol, such as

vodka, or cognac…

Let’s go on with experimental tests. What if acid were added to egg white? Is it true that acids “cook”

fish, like in fishes “a la Tahitienne”, or in cebiche? Of course, there are theoretical reasons to get a

result, as proteins have some amino acids residues whose electric charge depends on pH (a measure

of acidity or alkalinity, between 0 and 14). And when an egg is put into vinegar, there is first dissolution

of the shell, then a slow coagulation of the egg, producing a strange egg, after about one month. As

“one century years old eggs” are obtained in China by putting eggs in a mixture of clay, straw and lime

or ashes (containing potash, i.e. an alkali), we called our “acid cooked” eggs “minus one century years

old eggs”.

Are they “cooked”? Not if we follow to the definition given by the dictionary, according to which cooking

is a transformation induced by heat. This is why, in France, after an email poll for more than 1300

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