MODIFIED STARCH

According to Visakh and Yu (2016), starch is an abundant, inexpensive, renewable, and biodegradable polymer. Polymers are made up of numerous molecules strung together to form long chains. Starch is the second most abundant natural polymer after cellulose. Starch can be obtained mainly from the roots, stalks and seeds of staple crops such as maize, wheat, potato, cassava and rice. In these plants, starch is produced in the form of granules, and the size, shape, morphology, and composition of these granules vary from plant to plant. Maize, or maize starch, makes up the majority of the world market for starch, and most of this is produced in the United States of America. Europe is the major producer of wheat and potato starches, whereas cassava starch is mainly produced in Asia. Other starches, such as those from rice and sweet potato, make up only a minor proportion of the total. The common industrial starches are typically derived from cereals (maize, wheat, rice, sorghum), tubers (potato, sweet potato), roots (cassava) and legumes (mung bean, green pea). Sago palm and sugar palm starch are examples of commercial starch derived from another source, the palm stem. It has been reported that the USA, followed by Europe, are the two largest producers of starch in the world and contribute about half of the globally produced commercial starch. Worldwide, the main sources of starch are maize (82%), wheat (8%), potatoes (5%) and cassava (5%) (Visakh and Yu, 2016). Starch is a versatile polymer and therefore an important industrial material in both the food and non-food industries. Approximately, 60 million tons are extracted annually worldwide from various cereals, tubers and root crops, of which roughly 60% is used in the food industry (for example, bakery products, sauces, soups, confectionery, sugar syrups, ice cream, snack foods, meat products, baby foods, fat replacers, coffee whitener, beer, soft drinks) and 40% is used in pharmaceuticals and other industries, such as fertilizers, seed coatings, paper, cardboard, packing materials, adhesives, textiles, fabrics, diapers, bioplastics, building material, cement, and oil drilling (Visakh and Yu, 2016). In terms of its chemical composition, starch is a polysaccharide consisting of D-glucose units, referred to as homoglucan or glucopyranose, and has two major biomacromolecules namely amylose and amylopectin. Amylopectin is generally the major component of starch and constitutes 65–85% of the matter in the starch granules (Fredriksson et al. 1998; Gérard et al. 2001; Hoover 2001, as cited by Bertoft, 2015). Amylopectin is a much larger molecule than amylose and is a heavily branched structure. Modified starch is a food additive which is prepared by treating starch or starch granules, causing the starch to be partially degraded. The purposes of this modification are to enhance its properties particularly in specific applications such as to improve the increase in water holding capacity, heat resistant behavior,
reinforce its binding, minimized syneresis of starch and improved thickening. Modified starches consist of starch with low to very low level of substituent group. Enzymatic modification of starch is hydrolysis of some part of starch into a low molecular weight of starch called maltodextrin, or dextrin using amylolytic enzymes. They are widely used for food and pharmaceutical industries. Starch is an abundant carbohydrate distributed worldwide in plants. Starch has been a major ingredient in man’s diet over the centuries. In addition it has become a major industrial raw material. Plant seeds, roots and tubers are all sources of industrial starch production. The commercial realities of the starch recovery process limit the industrial sources mainly to wheat, maize and tapioca. Maize (Corn) contains about 70% starch, other components being protein, fibers and fat. The basis of the maize milling process is the separation of the maize kernel into its different parts. Maize starch is produced by the wet milling process, which involves grinding of softened maize and separation of corn oil seeds (germs), gluten (proteins), fibers (husk) and finally pure starch. The byproducts from maize based industries find various applications: i. Maize (Corn) Steep Liquor: It contains amino acids, proteins and are used by antibiotics drugs manufacturers. Also it is a large source of biogas, which is being used as fuel for driers, boilers etc. ii. Maize Gum: Corn Oil is produced by expelling oil from the germs. Corn Oil finds applications in food and other chemical industries. Maize oil cake obtained after expelling oil is used as cattle and poultry feeds. iii. Maize Gluten: Maize Gluten contains high protein content and it is used as cattle and poultry feeds. iv. Maize Husk: It contains starch, protein and fat as minor components and mainly consumed as cattle feed. Starch is a group of polysacchrides, composed of glucopyranose units joined together by-glucosidric linkages. It conforms to the molecular formula, (C6-H10O5)u, where n varies from a few hundred to over one million. Starch is found as the reserve carbohydrate in various parts of plants and is enzymatically broken down to glucose to other carbohydrates according to the metabolic needs of the plants. Industrially, starch is broadly divided into two types viz, natural and modified. Natural starches, also designated as unmodified starches or simply starches, are obtained from grains such as and sorghum. from roots like potato, tapioca and arrow root, and from the pith of the stems of certain palms such a sago. They are further classified into cereal starches and root starches. The characteristics of the natural starches are changed by chemical or enzymatic action and the products of these reactions are termed modified starches. This group includes dextrins, acid-modified starches, oxidized starches, starch esters, starch ethers, aldehyde starches and cationic starches. Starch occurs naturally in the plants and its percentage varies with the plant and also in different parts of the same plant. Corn (maize) sorghum grain wheat, rice, potato, tapioca, arrowroot and sago are among the important sources of natural starches. The grains of barley, rye, oat and the millets are also employed in the production of starches. The roots of tapioca plant (manihot utillissimax) froms one of the major sources of starch, ranking next to potato in the comimption by starch industry. Tapioca plant, also know as cassava and manioc, thrives in equatoraial regions between the Topic of Capricorn. There are as many as seventy five varieties of cassava plant of which two varieties viz., bitter and sweet are widely cultivated; the bitter is usually grown for the purposes if the manufacture of starch, as it contains a higher content of starch. The starch content of the plant varies between 12 and 33 per cent. The ratio of the percentage of amylase to amylopection has been found to be 16:84. More than hal of the total world arrange under the cultivation of cassava is confined to the African countries such as Gambia, Ghana, Kenya, Mauritius, Nigeria, Zambia, Nyssaland, Sierra Leone and Zanzibar and the rest come from the tropical regions of other continents. The cereal starches such as maize wheat, rice and sorghum are recovered by several processes, of which the wet-milling is by far the most important. Other processes commercially employed in the manufacture of unmodified starches are that alkali, Martin and batter in the order of decreasing importance. Of the material methods earlier used for the production of starch and which have now become obsolete, mention may be made of the Hakka, Alsation and Fescas processes. In all the above processes, Starch is recovered in five stages: a) Softening or steeping of the grains, after thorough washing in water. b) Tabling or centrifugation of the ground mass. c) Dewatering and drying of the final products. d) The recovery of important by products.