2.1.2 Starch
(Corn starch, Potato Starch, Rice Starch, Wheat Starch)
Synonym Amylum
Biological Source Starch comprises of mostly polysaccharide granules usually separated from the fully grown grains of Corn [Zea mays Linn.]; Rice [Oryza sativa Linn.] ; and Wheat [Triticum aestivum Linn.] belonging to the family Gramineae and also from the tubers of Potato [Solanum tuberosum Linn.] family Solanaceae.
Geographical Source USA, Canada, Australia, China, India, CIS – countries (Russia), Thailand, Indonesia, Vietnam, Pakistan and many other tropical and sub-tropical countries are the major producers of starch in the world.
Preparation In general, cereal grains e.g., corn, rice and wheat mostly comprise of starch bundles, oil, soluble protein and the insoluble protein termed as ‘gluten’; whereas the potato contains starch, mineral salts (inorganic), soluble proteins and vegetable tissues. Obviously, various specific methods are normally employed to separate starch either from cereal grains or from potato. These methods are briefly enumerated below, namely:
(a) Methods for Maize (Corn) Starch
Maize grains are first washed with running water to get rid of dust particles and adhered organic matters. They are now softened by soaking in warm water (40-60oC) for 48 to 72 hrs charged with a 0.2-0.3% solution of SO2 to check the fermentation. The swollen grains are passed through ‘Attrition Mill’ to split and partly crush them to separate the embryo and the epicarp. It is extremely important to isolate the germ (embryo) which may be accomplished by addition of water, whereby the germs float and are segregated by skimming off promptly. The corn oil, a rich source of Vitamin E, is recovered from the germ by the process of expression. After removal of the germ the resultant liquid mass is subsequently freed from the accompanying cell debris and gluten (insoluble protein) by passing through a number of fine sieves. The milky slurry thus obtained is a mixture of starch andgluten particles which is then subjected to centrifugation by custom-designed starch purification centrifuges. Thus, the starch which being relatively heavier settles at the bottom and the gluten being lighter floats on the surface and removed quickly by a jet of water. Consequently, the starch is washed thoroughly with successive treatment of fresh water, centrifuged or filter pressed and ultimately dried either on a moving belt dryer or flash dryer.
(b) Method for Rice Starch
The rice* is adequately soaked in a solution of NaOH (0.5% w/v) till such time when the gluten is softened and dissolved partially. The resulting grains are wet-milled and taken up with water. The suspension is purified by repeatedly passing through sieves and the starch is recovered by centrifugation. Finally, the starch is duly washed, dried, powdered and stored in HDPE** bags.
(c) Method for Wheat Starch
Wheat being an extensively used common staple food, therefore, its utility for making starch is restricted by many government authorities. First of all the wheat flour is made into a stiff ball of dough which are kept for a short duration. The gluten present in the dough swells up and are shifted to grooved-rollers that move forward and backward slowly. Constant sprinkling of water is done which carries off the starch along with it whereas gluten remains as a soft elastic mass. The shurry of starch is purified by centrifugation, washed, dried, powdered and packed in HDPE bags.
(d) Method for Potato Starch
The tubers of potato are thoroughly washed to get rid of the sticking soil. These are subsequently chopped into small pieces and made into a fine pulp by crushing in a Rasping Machine. The resulting
slurry is passed through metallic sieves to remove the cellular matter as completely as possible. The starch suspension (slurry) is purified by centrifugation, washed, dried and the stocked in HDPE bags.
Description
Starch occurs in nature as irregular, angular, white masses that may be easily reduced to power.
Appearance : White – rice and maize starch,
Creamy white – Wheat starch,
Pale yellow – potato starch,
Odour : Odourless
Taste : Bland and mucilaginous.
Nevertheless, all the four types of starch mentioned above do possess a definite shape and
characteristic features as illustrated in Fig. 3.1
Chemical Constituents
In general, under ideal experimental parameters hydrolysis of starch in acidic medium yields glucose in theoretical proportion that essentially represent the main building block of the starch molecule. It has been established that starch molecule is essentially made up of two complex polysaccharides, namely:
(a) Amylopectin: (α-Amylose)
Amylopectin is insoluble in water and swells in it thereby giving rise to a thick paste upon boiling with water. It produce a distinct violet or bluish red colouration with iodine* solution (0.1 N). It has a highly branched structure that is composed of several hundred short chains of about 20-25 D-Glucose units each. Interestingly, one terminal of each of these chains is joined through C-1 to a C-6 with the next chain and so on and so forth as shown below:
(b) Amylose: (β-Amylose)
Amylose is water soluble and gives an instant bright blue colour with iodine solution (0.1 N). Based on the fact that amylose upon hydrolysis yields the only disaccharide (+) – Maltose and the only monosaccharide D-(+) – Glucose, it has been suggested that amylose is comprised of chains of a number of D-(+) – glucose units, whereby each unit is strategically linked by an alpha–glycoside bondage to C-4 of the next unit as depicted below:
Amylose invariably constitutes upto 25% of the total starch content; however, the proportion varies with the particular species under consideration. Amylose is found to be either absent or present to a very small extent (≤ 6%) in some glutinous or waxy starches available in the plant kingdom.
Substituents and Adulterants
A number of biological species containing starch is generally employed to substitute (adulterate) the conventional commercially available starch used as food and as pharmaceutical adjuvants, namely:
Uses
1. It possesses both absorbent and demulcent properties.
2. It is employed in dusting powder because of its unique protective and absorbent property.
3. It is used in the formulation of tablets and pills as a vital disintegrating agent and a binder.
4. It is utilized as a diagnostic aid for the proper identification of crude drugs.
5. It is employed as a diluent (or filler) and lubricant in the preparation of capsules and tablets.
6. It is used as an indicator in iodimetric analyses.
7. It is an antidote of choice for iodine poisoning.
8. Dietetic grades of corn starch are marked as ‘Maizena’ and ‘Mondamin’.
9. ‘Glycerine of starch’ is used not only as an emolient but also as a base for the suppositories.
10. It is the starting material for the large scale production of liquid glucose, glucose syrup, dextrose and dextrin.
11. It finds its extensive industrial application for the sizing of paper and textile.
12. It possesses nutrient properties as a food and in cereal based weaning foods for babies e.g.,
Farex(R) (Glaxo) and Cerelac(R) (Nestle).
13. It is used topically and externally to allay itching.
14. It is used profusely in laundry starching.
* Broken pieces of rice obtained during the polishing are mostly used for preparation of rice starch.
** HDPE : High density polyethylene.
REFERENCES
Ashutosh Kar (2003), Pharmacognosy and Pharmaco biotechnology, 2nd Edition
‘Handbook of Medicinal Herbs’ (2001), J.A. Duke, CRC-Press, London, 1st Edn.
William Charles Evans (2002), Trease and Evans Pharmacognosy 15th Edition by: Trease, Bailliere Tindall; Evans.
Ramstad (1956), E., ‘Modern Pharmacognosy’, McGraw Hill, London.
