Somethings about starch

Lavinia | 26 October 2008 | no comments | 11,189 afisari

Starch is a polysaccharide carbohydrate consisting of a large number of glucose monosaccharide units joined toghether by glycosidic bonds, with chemical formula (C₆H₁₀O₅)_n.

Starch has many chemical and physical characteristics that set it apart from other food components and give it numerous applications. Food processors and other industrial users should be familiar with starch‘s structural and behavioral characteristics so as to make use of its properties. The chemestry and technology of starch has been reviewed in detail.

Unlike other carbohydrates and edible polymers, starch occurs as discrete particles called starch granules. These particles are unique to the plant source and, therefor, starch from every plant type is different in appearance, properties, and particle size distribution. Microscopists can readily identify the plant source of most commercial starches.

Starch in granular form is generally composed of two types of molecules:

amylose – is a linear (1, 4)-α-D-glucan
amylopectin – is a branched, bushlike structure containing (1, 4)-α-D linkages between D-glucose residues and (1, 6)-α-D branch points.

Normal starches contain about 75% amylopectin molecules. Amylopectin is a much larger molecule than amylose, as shown below:

Property	Amylose	Amylopectin
Molecular mass	5000-200000	One to several million
Glycosidic linkages	Mainly (1, 4)-α-D-	(1,4)-α-D-, (1,6)-α-D-
Susceptibility to retrogradation	high	low
Products of action of β-amylase	Maltose	Maltose, β-limit dextrin
Products of actions of glucoamylase	D-glucose	D-glucose
Molecular shape	essentially	Bush-shaped

It is these characteristic molecular sizes, amylose – amylopectin ratios, and granular structures which give each type of starch its unique properties.

Plants grown for starch production include corn, sorghum, wheat, rice, tapioca, arrowrrot, sago and potato. Other noncommercial sources of starch include quinoa and amaranth, whose starches have been isolated and examined with respect to chemical and physical characteristics and possible use.