What is "retrogradation"

Retrogradation \Re`tro*gra*da"tion\, n. [F. r['e]trogradation or L. retrogradatio. See Retrograde.]

1. The act of retrograding, or moving backward.

2. The state of being retrograde; decline.

n. 1 Motion in a retrograde manner 2 decline, degradation 3 (context chemistry English) A reaction that takes place in gelatinized starch when the amylose and amylopectin chains realign themselves, largely responsible for bread becoming stale.

Retrogradation is the landward change in position of the front of a river delta with time. This occurs when the mass balance of sediment into the delta is such that the volume of incoming sediment is less than the volume of the delta that is lost through subsidence, sea-level rise, and/or erosion. As a result, retrogradation is most common:

• during periods of sea-level rise which results in marine transgression. This can occur during major periods of global warming and the melting of continental ice sheets.
• with extremely low sediment input.

Retrogradation is a reaction that takes place when the amylose and amylopectin chains in cooked, gelatinized starch realign themselves as the cooked starch cools.

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 a 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.

Retrograded starch is less digestible (see resistant starch).

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