Retrogradation (starch)

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Retrogradation is a reaction that takes place in gelatinized starch when the amylose and amylopectin chains realign themselves, causing the liquid to gel.

When native starch is heated and dissolves in water, the crystalline structure of amylose and amylopectin molecules is lost and they hydrate to form a viscous solution. If the viscous solution is cooled or left at lower temperature for long enough period, the linear molecules, amylose, and linear parts of amylopectin molecules retrograde and rearrange themselves again to a more crystalline structure. The linear chains place themselves parallel and form hydrogen bridges. In viscous solutions the viscosity increases to form a gel. At temperatures between –8 and +8 °C the aging process is enhanced drastically.

Retrogradation can expel water from the polymer network. This is a process known as syneresis. A small amount of water can be seen on top of the gel. Retrogradation is directly related to the staling or aging of bread.[1]

Retrograded starch is linked to a reduction in colon cancer.[2] Retrograded starch is less digestible (see resistant starch).

Chemical modification of starches can reduce or enhance the retrogradation. Waxy, high amylopectin, starches have also much lesser tendency to retrogradate. Additives such as fat, glucose, sodium nitrate and emulsifier can reduce retrogradation of starch.

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References[edit]

  1. ^ Cereals in breadmaking: a molecular colloidal approach, Ann-Charlotte Eliasson, Kåre Larsson, CRC Press, 1993, pages: 126-129, ISBN 0-8247-8816-8, ISBN 978-0-8247-8816-2
  2. ^ [1] Retrograded high amylose corn starch reduces cholic acid excretion

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