Starch is a polysaccharide of plant origin. It is digestible in the human GI tract and therefore has great importance in human nutrition.
Starch makes an efficient energy store in plants. It does not have sweet taste like monosaccharides and disaccharides. The plants store starch in cereal seeds and tubers (eg. potatoes) in the form of starch grains that are specific to a particular plant species.
Grains contain 66-85%, pulses contain 60% and potatoes contain 20-30% starch. Unripe fruit contains starch that breaks down to simple sugars during maturation.
Starch is made up of two main types, both are made of long chains of glucose. These are amylose and amylopectin. Amylose is made of linear chains, and amilopectin has a branched structure. The amylose – amylopectin ratio depends on the type of plant. The majority of the starch has a 15-30% amylose.
Amylose and amylopectin in the starch granules are in semicrystalline form that makes the granules water-insoluble. Upon cooking this structure is degraded, and the polysaccharide chains become available to digestive enzymes in the human gut.
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