Молекулярная гастрономия для креативных шеф-поваров (англ. язык) - страница 28

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

cellulose molecules to lie closely together and form very rigid structures.

Effect of heat:

Unlike the other fibres, cellulose is not chemically broken down by heat or pH.

IV/V - 2 (of 3)

Hemicellulose

Hemicellulose is a polymer consisting of several different simple sugars (including glucose, xylose,

mannose, rhamnose, arabinose and galactose).

Effect of heat:

During cooking the hemicelluloses will break down into their constituent sugars.

Pectin

Pectin is another polysaccharide made up of many molecules of _-Galacturonic acid, a sugar unit that

resembles a modified glucose unit.

Effect of heat:

In the presence of heat, these large chains are chemically degraded into soluble molecules, which are

released from the cell wall, helping the cell wall to break down. In addition to heat, pH plays an

important role in pectin degradation.

Effect of pH:

In the presence of alkali, the degradation of pectin due to heat is much more pronounced. Alkali

causes the ionisation of the COOH groups, to form COO- groups, which will repel each other,

favouring their separation and release from the cell wall.

Acid however, strengthens pectin. In an acidic environment, any COO- groups will acquire hydrogen

ions, to form neutral COOH groups, and the pectin molecules will remain neutral. This reduces

repulsion between pectin molecules, so they will tend to stay associated and be prevented from

degrading so readily when heated.

...
ps, and the pectin molecules will remain neutral. This reduces

repulsion between pectin molecules, so they will tend to stay associated and be prevented from

degrading so readily when heated.

Starches

There are two main sorts of starch molecule found in vegetables:- amylose and amylopectin. Both are

composed of long chains of glucose molecules, but they differ in how the glucose molecules are linked

together.

Amylose exists as a long unbranched chain of glucose molecules, containing usually between 250 and

2000 glucose molecules. It is found coiled in the shape of a helix. A section of its structure is shown

below:

Amylopectin chains however are highly branched, with short side chains of about 30 glucose units

attached regularly along the chain. Amylopectin molecules are therefore much larger, and may contain

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