Starch and Starch Granules

Abstract

Starch is the main form in which plants store carbon. It occurs as semi‐crystalline granules composed of two polymers of glucose, called amylose and amylopectin. Depending on the plant organ, it can act as a store of carbon for lengths of time as short as a day (e.g. in leaves) or as long as many years (e.g. in dormant seeds). Starch granules are characterised by internal growth rings. There is enormous variation in granule size and shape between plant organs, and between species. Starch is the major carbohydrate of nutritional importance in the diet: it is degraded to glucose by amylases in the mouth and small intestine. When cooked in water, starch forms gels or pastes that have a wide range of industrial applications in both food and nonfood industries.

Key Concepts:

  • Starch is the main form in which plants store carbon.

  • Starch occurs as semicrystalline granules, composed of branched and linear polymers of glucose.

  • Starch granules vary in size and shape between plant organs and between species.

  • The distinctive morphology and anatomy of starch granules enables the identification of plant remains in food, forensic and archaeological samples.

  • Starch is the main component of the harvested parts of many crops, including cereals, peas and beans, potatoes and cassava.

  • Starch is the main carbohydrate of nutritional importance in the human diet.

  • When cooked in water, starch granules swell to form gels or pastes that are widely used in food and nonfood industries.

  • Major uses for starch include a thickener in processed foods, and in the manufacture of paper, biodegradable plastics and adhesives.

  • Starch is often modified after extraction to generate properties desirable for specific industrial purposes: there is interest in breeding new crops in which the native starch already has these properties.

Keywords: starch granule anatomy; starch granule morphology; industrial uses of starch; starchy foods; starch properties

Figure 1.

Transmission electron micrograph showing starch granules inside two chloroplasts in a mesophyll cell of an Arabidopsis leaf. The bar represents 0.5 μm. Courtesy of Sue Bunnewell, John Innes Centre.

Figure 2.

Starch granules from the endosperm of cereal seeds. (a) Light micrograph showing compound starch granules within an endosperm cell of an oat seed (courtesy of Tamara Verhoeven and Kay Denyer, John Innes Centre). Note that each compound granule is made up of several smaller granules. (b) Scanning electron micrograph of a fracture face of a barley seed, showing tightly packed A and B granules within endosperm cells ( courtesy of Thomas Howard, John Innes Centre). The bar represents 20 μm. (c) Scanning electron micrograph of maize starch ( courtesy of Emma Pilling, John Innes Centre). The bar represents 10 μm. (d) Scanning electron micrograph of wheat starch ( courtesy of Emma Pilling, John Innes Centre). Note the presence of both large A granules (the arrows indicate equatorial grooves) and small B granules. The bar represents 50 μm.

Figure 3.

Light micrographs of starch granules from potato tubers. (a) Growth rings within a granule, visible in transmitted light. (b) Birefringence (Maltese cross) visible in polarised light.

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Further Reading

BeMiller JN and Whistler RL (eds) (2009) Starch Chemistry and Technology, 3rd edn. New York. Elsevier and Academic Press.

Deschamps P, Moreau H, Worden AZ, Dauvillée D and Ball SG (2008) Early gene duplication within Chloroplastida and its correspondence with relocation of starch metabolism to chloroplasts. Genetics 178: 2373–2387.

Langeveld SMJ, van Wijk R, Stuurman N, Kijne JW and de Pater S (2000) B‐type granule containing protrusions and interconnections between amyloplasts in developing wheat endosperm revealed by transmission electron microscopy and GFP expression. Journal of Experimental Botany 51: 1357–1361.

Regina A, Bird A, Topping D et al. (2006) High‐amylose wheat generated by RNA interference improves indices of large‐bowel health in rats. Proceedings of the National Academy of Sciences of the USA 103: 3546–3551.

Torrance R and Barton H (eds) (2006) Ancient Starch Research, Walnut Creek, CA: Left Coast Press.

Zeeman SC, Kossmann J and Smith AM (2010) Starch: its metabolism, evolution and biotechnological modification in plants. Annual Review of Plant Biology 61 doi: 10.1146/annurev‐arplant‐042809‐112301.

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How to Cite close
Smith, Alison M(May 2010) Starch and Starch Granules. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001294.pub2]