Молекулярная гастрономия для креативных шеф-поваров (англ. язык) - страница 139

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

different types of vegetable varies according to the type of vegetable, different vegetables undergo

different texture changes when subjected to the same amount if heat (for example, the difference in

the texture of lettuce before and after boiling for a minute is much more pronounced the texture

change in carrots after boiling for only one minute).

Changes to cellulose: Cellulose is a polymer of glucose arranged in long straight chains. The absence

of side chains allows cellulose molecules to lie closely together and form rigid structures – the

cellulose is responsible for the toughness of the plant cell wall. As the cells are heated up, the

cellulose softens (but is not chemically modified), weakening the cell wall. This reduces the cells ability

to keep in its water, which then leaves, causing the plant to wilt.

Vegetables containing lots of cellulose will remain crisper after cooking, but will need to be cooked for

longer to obtain the desired tenderness. Vegetables low in cellulose will not remain firm after cooking.

Changes to pectin: Pectin acts as a glue to hold plant cells together. During cooking the pectic

polymers are chemically degraded into soluble molecules, which are released from the cell wall

causing the cell wall to weaken. This process is emphasised in the presence of alkali. Alkali causes

the ionisation of the -COOH groups from pectines, forming -COO- groups, which repel each other

favouring their separation and thus the degradation of cell walls.

Acid, however, strengthens pectin. In an acidic environment, pectin molecules are neutral – any

existing -COO- groups will acquire a hydrogen ion, forming neutral -COOH groups. This reduces

repulsion between pectin molecules, which are now all neutrally charged, so they stay associated and

are less likely to dissolve so readily when heated.

Changes to hemicellulose: During cooking the hemicelluloses break down into their constituent

sugars, further reducing cell wall strength.

Overall: ,All the above changes cause the cell wall to soften during cooking and becomes porous, and

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