Молекулярная гастрономия для креативных шеф-поваров (англ. язык) - страница 229

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

On the contrary, no calculation can ever tell if lard is better than oil or butter, if chestnut flour is better

than rice flour, etc.

What does cooking mean?

Having shown that we do not need fixed recipes, let’s come to the main point of culinary craft: cooking.

What is cooking? Let’s consider first cooking eggs and move later to meat, fish and vegetables or

fruits.

In boiling water, an egg white looses its transparency and yellow color to become white; it loses its

liquid consistency to become solid. Why?

The preliminary experiment of heating an egg white (about 30 g) in a pan shows that egg white is

made of two parts: first water, forming a white smoke over the pan, makes 90 percent of the white; in

the pan, after evaporation of water, a yellow solid sheet is primarily made of proteins (about 3 g).

As water does not coagulate, it has to be admitted that proteins are responsible for the coagulation of

egg white when heated. Why? Chemical studies have shown that proteins are like coiled open

necklaces; the pearls are amino acid residues, of which two major kinds exists: hydrophilic ones and

hydrophobic ones. In water, proteins reduce their energy by coiling so that the hydrophobic segments

of the protein are in the centre, surrounded by hydrophilic parts.

These proteins do not retain their fixed coiling, as water molecules are perturbing the coiling. When

the kinetic energy associated to heat is greater than the coiling energy,...

r molecules are perturbing the coiling. When

the kinetic energy associated to heat is greater than the coiling energy, proteins uncoil, and expose

their thiol groups –SH of cystein amino acids; under oxidizing circumstances, these groups react to

form disulfide bridges (-S-S-) that link proteins together.

Figure 4. When proteins (with hydrophobic core, in red, and hydrophilic parts, in pink) uncoil,

they can link because sulphur atoms make “disulfide bridges”. Linking of proteins is

responsible of the formation of a protein network, in which water from egg whites are trapped.

In the heated egg white, linked proteins form a network where water molecules are trapped. This is

called a gel (more precisely a chemical gel, as disulfide bridges are strong forces, and chemical gels

Страницы: Пред. | 1 | ... | 227 | 228 | 229 | 230 | 231 | ... | 253 | След.

Еще статьи