Principles of Cereal Science and Technology, Third Edition
Transitory starch is produced by photosynthesis in green leaves. Shortly after production, it is degraded to sucrose and, in the case of cereals and legumes, transported to seeds, where it is laid down in the endosperm tissue as water-insoluble granules that serve as the plant's main storage carbohydrate. The amyloplasts, which synthesize the starch, possess all the enzymes necessary for granule formation. From an osmotic standpoint, it is a great advantage for the plant to store its excess energy as starch, which is insoluble and of extremely high molecular weight, rather than as sucrose. The level of starch in a cereal grain varies but is generally between 60 and 75% of the weight of the grain.
Grain is an important part of the human diet, as much of the food that humans consume is in the form of starch. Starch is a major constituent of many food products, including bread, breakfast cereals, cooked rice, and pasta.
Starch can be degraded to glucose, which provides the body with an important source of energy. In addition, starch is important because of its effect on the physical properties of many of our foods. For example, the gelling of puddings, the thickening of gravies, the structure of bread crumb and its staling, and the setting of cakes are all strongly influenced by the properties of starch. Starch is also converted industrially into starch syrups, which are used as sweeteners in food and soft drinks as well as in several fermentation processes. Starch is also an important industrial commodity, particularly in the papermaking industry and for producing ethanol as a fuel or fuel additive.
This chapter focuses on the structure and properties of starch.