Retrogradation of starch

· When the amylose and amylopectin chains realign themselves, causing the liquid to gel, generally an undesirable effect.
· When native starch is heated and dissolves in water, the crystalline structure of amylose and amylopectin molecules are 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.
· 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.

Sources of Starch

Natural sources and Modified:

1. corn
2. tropica
3. wheat
4. sweet potato
5. sago
6. rice
7. yucca

Modified Starches:


· A modified starch is a starch that has been chemically modified. To produces such a starch that function properly under these conditions.


(1). High heat/or shear (2). Storage conditions (cooling)

· Acid-treated starch
· Alkaline-treated starch
· Bleached starch
· Oxidized starch
· Starches, enzyme-treated

PHotosynthesis

Starch and Photosynthesis


· Photosynthesis - 'Photo' refers to light and 'synthesis' means preparation.
· In photosynthesis plants use light energy to produce glucose from carbon dioxide.
· Sore in the form of starch granules, in plastids such as chloroplasts and especially amyloplasts.
· Glucose is soluble in water, bind much water and ashes.


6CO2 + 6H2O ® C6H12O6 + 6O2

· Glucose in the form of starch, on the other hand, is not soluble and can be stored much more compactly.
· Glucose molecules are bound in starch by the easily hydrolyzed alpha bonds.

Histry of starch

· Wheat paste was used by Egyptians to stiffen cloth and during weaving linen.
· Romans used in cosmetic creams, powder the hair.
· Persians and Indians used it to make dishes.
· Chines use rice starch as a surface treatment of the paper.

what is Starch?

· Starch is derived from Middle English (Strechen) means stiffen.
· Amylose is Latin from Greek and Amulon, which means, “not ground at a mill”.
· Starch or amylum is a polysaccharide carbohydrate consisting of a large number of glucose units joined together by glycoside bonds.
· Starch is produced by all green plants as an energy store and is a major food source for humans.
· Starch is white, tasteless and odorless powder.
· Insoluble in cold water but soluble in alcohol and hotwater.
· It consists of two types of molecules helical amylose and branched amylopectin.
· Depending on plant starch generally contains 20% to 25% amylose and 75% to 80% amylopectin.
· Starch can be used as a thicking, stiffening or gluing agent when dissolved in warm water.