starch

Starch is a carbohydrate storage polysaccharide found in many plants. It consists primarily of glucose units linked by α-1,4 glycosidic bonds in long chains, with occasional α-1,6 branches forming amylopectin. The two main components are amylose (mostly linear) and amylopectin (highly branched). Starch is stored as microscopic granules within plastids of plant tissues, size and composition varying by source.

Commercial starch is abundant in cereal grains such as maize, wheat, and rice, and in tubers such as potatoes and cassava. It is recovered by mechanical extraction and washing to produce a starch slurry, which can be dried to a powder. Different sources yield starches with distinct gelatinization and rheological properties.

Starch granules are semi-crystalline and absorb water when heated. Upon heating in water, starch gelatinizes as granules swell and leak amylose, thickening the mixture. Gelatinization temperatures depend on source and amylose content, typically in the 50-80 C range. After cooling, amylose can recrystallize, causing gel formation and retrogradation.

In nutrition and cooking, starch provides energy and acts as a thickener, binder, or texture modifier in foods. Its digestibility is influenced by the amylose-amylopectin ratio and processing; foods can contain rapidly digestible, slowly digestible, or resistant starch, the latter behaving like dietary fiber in the gut.

Industrial and nonfood uses include paper manufacture, textile sizing, and adhesives. Starches can be chemically or physically modified to improve stability, clarity, tensile strength, or heat resistance for specific applications.