Notes_On_STARCHES.docx

**STARCHES** Starches are the first visible product of photosynthesis. They serve as food reserve and store of energy in higher plant and have the general characteristics of being insoluble in cold water, alcohol and give a blue black coloration with iodine. They can categorized as unorganized drug...

**STARCHES** Starches are the first visible product of photosynthesis. They serve as food reserve and store of energy in higher plant and have the general characteristics of being insoluble in cold water, alcohol and give a blue black coloration with iodine. They can categorized as unorganized drugs with organized structures. **General properties** - They are organized structures which vary in shape (spherical, polygonal, elliptical etc) and size (1 - 100µm in diameter). - The shape and size of starch is a characteristic feature of the plant species and the level of maturity of the plant. - Microscopical examination reveals that starch granules consist of concentric layer of arranged around a spot which is generally eccentrically located (i.e off the center) called the helium. - On heating with water, the granules swell or gelatinize, eventually producing an aqueous paste; depending on the concentration of the starch. **NOTE:** The temperature at which gelatinization occurs (usually in the range of 60 - 80ºC) is a function of the source of the starch. Most starches are a granular mixture of 2 polysaccharides- namely, AMYLOSE and AMYLOPECTIN. Both are polymers of α- d- glucopyranose but differ in the way in which the constituents monosaccharides are arranged. Amylose is helical in structure and constitute about 15- 25% of most starches, however, in sorghum and maize, it is less than 1%, while in wrinkled pear, it amounts to 50 -75%. The two starch components can be separated by ***SELECTIVE PRECIPITATION***. **GENERAL PROPERTIES OF COMMERCIAL STARCH** Although all starches may appear to be the same physically, they can be distinguished by the following characteristics 1. Shape of the grain- this may be spherical, elliptical, ovoid or polygonal. 2. Size of the grain -- the size of the grain may vary from 1- 2 to 100µm in diameter. 3. 3\. The position of the Helium- the position of the point of growth may be central or eccentric. In some cases, there may be 2 points of growth in a single grain. Such examples are referred to as half-compound e.g potato starch. 4. Shape of Helium: the shape of the helium may be spherical, (potato), cross-shaped as in (*Maranta arundinaceae* - arrowroot) and /or three or four angled fissure or cleft as in maize. It may be indistinct or wanting (wheat). 5. Reaction with Iodine- the colour observe vary from blue black in most cases to red to yellowish red as seen with amylodextrin. Amylose binds most of the Iodine, about 20X more than Amylopectin. Amylopectin in the absences of amylose displays a reddish-brown color 6. Gelatinization temperature- the temperature at which gelatinization takes place varies in starch as well as the consistency of the paste formed. 7. View under polarized light- when observed under polarized light, starch grains reveals a characteristic maltese cross. The degree of the colour produced also varies considerably. For the purpose of the Pharmaceutical industry, a number of starches are recognized. These include; Maize starch Rice starch Potato starch Arrowroot starch Tapioca starch ASSIGNMENT\-\--INPUT THE BOTANICAL NAMES OF THEPLANTA FROM WHICH STARCH MENTIONED ABOVE ARE SOURCED. **MICROSCOPY OF STARCH** 1. OCCURANCE -- They occur as irregular angular masses or as white powder. The size, shape and structure of starch granules from a particular plant only vary within definite limits \-\--making it possible to distinguish starch from different species 2. Starch granules may be simple, or compound.... the description 2- 3- 4- 0r 5- compound only refer to the number of component granules present in the compound granules. In some cases, compound granules are formed by the aggregation of a large number of simple granules e.g rice and cardamons. 3. Starting point of formation of the starch granules in the leucoplast is the helium. Starch granules are built by the deposition of successive layers around the helium and concentric layers and striations are often clearly visible. 4. The position of the helium and presence/absence of well -defined striation are of characteristic importance. Examples of some Pharmaceutical starches and their Characteristics **Corn starch** **Botanical source:** Corn starch is derived from *Zea mays*, family gramineae. It is by far the most common starch grain encountered in the indoor environment. It is used in paper sizing, coating plastics, coating candy, as a body powder, as a carrier for fragrances and pesticides, as an in extender coatings and paints, a mold-release in formed polymer manufacture, and many other uses. Characteristic Features: Corn starch tends to be polyhedral to sub-spherical in shape and generally 10 to 20 micrometers in diameter. The center vacuole (helium) may be spherical but is generally an elongated scar with pointed ends. It may have from 2 to 5 points forming a slit or star-like structure. There are no striations. Of note is the fact that starch from the inner meaty endosperm and outer horny endosperms differed in shape and to some extent size. Starch from the inner endosperm are polyhedral or sub-spherical, whereas, that from the outer endosperm is mortar shaped and polygonal. **Wheat starch:** Starch is the most important carbohydrate and a major component of wheat grain, which contains about 63-66% starch. Wheat starch granules are classified into three groups regarding their size; A- type , B-type and C-type granules. The A-type granules have a lenticular shape and a diameter greater than 15 μm, while the B-type are spherical and have a size range of 5-15 μm, and C-type (less than 5 μm) granules are spherical. Helium is present, centralized, seldom cleft with the presence of faint striations. Wheat starch normally contains 25-28% amylose and 72-75% amylopectin. The content of amylose in wheat flour plays an important role in the quality, because the ratio of amylase to amylopectin can affect the physicochemical properties of starch (texture, stability and viscosity of processed foods). **Rice starch** These consist of compound granules with angular outline and form 2 -- about 150 components granules. They are polyhedral with sharp angle and range in size from 3 -8 µm. helium is present, centralized and very conspicuous, but there are no striation. **Arrowroot starch** Most are simple, often tuberous and granules are oval or ellipsoidal. Helium is in the form of 2-rayed cleft, fine and the striations are concentric. **Tapioca starch** These are mostly simple sub-spherical muller shaped, round or polyhedral. They range in size from 5 - 35µm. The helium is punctuate or cleft and there are concentric striations. Potato starch These are simple, irregular, ovoid or spherical. They range in size from 30 - 100µm.The is present, eccentric. **Revision questions** 1. Give five general characteristics of starch. 2. By what means can amylopectin be separated from amylose 3. Give two examples of plants where the starch grains are aggregated to a large extent. 4. What is the shape of the helium in maranta starch. 5. When there are two point of growth in a starch grain, it is referred to as what? 6. Starch without the presence of amylose will give what colour reaction with iodine 7. What is the percentage composition of amylose and amylopectin in wheat starch. 8. The helium in arrowroot starch is \-\-\-\-\-\-\-\-\-\-\-\-\-- 9. Distinguish between starch from the inner and outer endosperm of maize. 10. Starch in general can be referred to............................... With.....................structures