Starch is an important constituent of the human diet and, for this purpose, is used chemically and enzymatically processed into a variety of different products such as starch hydrolysates, glucose syrups, fructose, maltodextrin derivatives or cyclodextrins, used in food industry. In addition to that, the sugars produced can be fermented to produce ethanol. In spite of the large number of plants able to produce starch, only a few plants are important for industrial starch processing. The major industrial sources are maize, tapioca, potato, and wheat, but limitations such as low shear resistance, thermal resistance, thermal decomposition and high tendency towards retro gradation limit its use in some industrial food applications. Among carbohydrate polymers, starch is currently enjoying increased attention due to its usefulness in different food products. Starch contributes greatly to the textural properties of many foods and is widely used in food and industrial applications as a thickener, colloidal stabilizer, gelling agent, bulking agent and water retention agent. Starch is a polymer of glucose linked to another one through the glycosidic bond. Two types of glucose polymers are present in starch: amylose and amylopectin. Amylose and amylopectin have different structures and properties. Amylose is a linear polymer consisting of up to 6000 glucose units with Î±-1,4 glycosidic bonds. Amylopectin consists of short Î±-1,4 linked to linear chains of 10-60 glucose units and Î±-1,6 linked to side chains with 15-45 glucose units. Granule bound starch synthase can elongate malto-oligosaccharides to form amylose and is considered to be responsible for the synthesis of this polymer. Soluble starch synthase is considered to be responsible for the synthesis of unit chains of amylopectin. Î±-Amylase is able to cleave Î±-1,4 glycosidic bonds present in the inner part of the amylose or amylopectin chain. Plants produce starch by first converting glucose 1-phosphate to ADP-glucose using the enzyme glucose-1-phosphate adenylyltransferase. The starch synthase then adds the ADP-glucose via a 1,4-alpha glycosidic bond to a growing chain of glucose residues to produce amylose. Starch branching enzyme introduces 1,6-alpha glycosidic bonds between these chains, creating the branched amylopectin. The starch debranching enzyme isoamylase removes some of these branches. Hence, several isoforms of these enzymes exist, leading to a highly complex synthesis process.
About Author / Additional Info:
Dr. Kirti Rani Sharma,
Assistant Professor (II),
Amity Institute of Biotechnology,
Amity University Uttar Pradesh, Noida
Sec-125, Gautam Buddha Nagar, Noida-201303 (UP), India.
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