Starch

STARCH

Synonyms

Amylum.

Biological Source

Starch consists of polysaccharide granules obtained from the grains of maize (Zea mays Linn.); rice (Oryza sativa Linn.); or wheat (Triticum aestivum Linn.); belonging to family Gramineae or from the tubers of potato (Solanum tuberosum Linn.), family Solanaceae.

Geographical Source

Most of tropical, as well as, sub-tropical countries prepare starch commercially.

Preparation of Starch

Depending upon the raw material to be used for processing or type of the starch to be produced, different processes are used for the commercial manufacture of starch.

Potato Starch: The potatoes are washed to remove the earthy matter. They are crushed or cut and converted into slurry. Slurry is filtered to remove the cellular matter. As potatoes do not contain gluten, they are very easy to process further. After filtration, the milky slurry containing starch is purified by centrifugation and washing. Then, it is dried and sent to the market.

Rice Starch: The broken pieces of rice resulted during the polishing are used for processing. The pieces of rice are soaked in water with dilute sodium hydroxide solution (0.5%), which causes softening and dissolution of the gluten. After this, the soaked rice pieces are crushed and starch prepared as described under potato starch.

Maize Starch (corn starch): Maize grains are washed thoroughly with water to remove the adhered organic matter after which they are softened by keeping in warm water for 2–3 days. Sufficient sulphur dioxide is passed to the medium to prevent fermentation. The swollen kernels are passed through attrition mill to break the grains, so as to separate the endosperm and outermost coating of the grains. At this point, special attention is given to separate the germ (embryo). This is effected by addition of water, wherein germs float and are separated. The water which is used to soften the grains dissolves most of the minerals, soluble proteins and carbohydrates from the grains. The water, being rich in all these contents, is used as a culture medium for the production of antibiotics like penicillin (corn steep liquor). The separated germs are used to prepare the germ oil by expression method and are known as corn oil. The oil contains fatty acids like linoleic and linolenic acids and vitamin E. It is used commercially, for the prepa-ration of soap. The starchy material contains gluten; most of this is removed by simple sieving and then by washing. Starch being heavier, settles at the bottom and is followed by gluten. Several treatments with cold water wash the starch effectively, which is then centrifuged or filter-pressed and finally, dried in flash dryers on a moving belt dryer.

Wheat Starch: Wheat being the major article of food is restrictedly used for preparation of starch. In this process, the wheat flour is converted into dough and kept for-a-while. The gluten in the dough swells and the masses are taken to grooved rollers, wherein water is poured over them with constant shaking. The starchy liquid coming out of the rollers is processed conveniently to take out the starch, which is then dried and packed suitably.

Description

Microscopic Characters

Rice Starch: The granules are simple or compound. Simple granules are polyhedral, 2–12 μ in diameter. Compound granules are ovoid and 12–30 μ × 7 to 12 μ in size. They may contain 2–150 components.

Wheat Starch: Simple lenticular granules which are cir-cular or oval in shape and 5–50 μ in diameter. Granules contain hilum at the centre and concentric faintly marked striations. Rarely, compound granules with two to four components are also observed.

Maize Starch: Granules are polyhedral or rounded, 5–31 in diameter, with distinct cavity in the centre or two to five rays cleft.

Potato Starch: Generally, found in the form of simple granules, which are sub-spherical, somewhat flattened irregularly ovoid in shape. Their sizes vary from 30–100 μ. Hilum is present near the narrower end with well-marked concentric striations.

           Starch grains obtained from the different sources

Chemical Constituents

Starch contains chemically two different polysaccharides, such as amylose (β-amylose) and amylopectin (α-amylose), in the proportion of 1:2. Amylose is water soluble and amylopectin is water insoluble, but swells in water and is responsible for the gelatinizing property of the starch. Amylose gives blue colour with iodine, while amylopectin yields bluish black colouration.

Identification Tests

1.     Boil 1 g of starch with 15 ml of water and cool. The translucent viscous jelly is produced.

2.     The above jelly turns deep blue by the addition of solution of iodine. The blue colour disappears on warming and reappears on cooling.

Uses

Starch is used as a nutritive, demulcent, protective and as an absorbent. Starch is used in the preparation of dusting talcum powder for application over the skin. It is used as antidote in iodine poisoning, as a disintegrating agent in pills and tablets, and as diluent in dry extracts of crude drug. It is a diagnostic aid in the identification of crude drugs. Glycerin of starch is used as an emollient and as a base for suppositories. Starch is also a starting material for the commercial manufacture of liquid glucose, dextrose and dextrin. Starch is industrially used for the sizing of paper and cloth.

Substitutes and Adulterants

Tapioca starch or Cassava or Brazilian arrowroot- This starch is obtained from Manihot esculenta (Euphorbiaceae) and is used as substitute for starch.