Starch is a carbohydrate (polysaccharide) consisting of a large number of glucose units. It is found in the storage organs of many plants. It is the main energy component of most staple foods, including cereal grains (wheat, maize, barley, rye, rice, oats, sorghum, millet), roots and tubers (potatoes, cassava, sago, arrowroot) (Daniel et al., 2007). It is also found in many legume grains (peas, faba beans, common beans) and in some fruits. In the cell, starch is stored in amyloplasts and forms starch granules. Starch is arranged in two types of macro-molecules: amylose (linear and helical polymer) and amylopectin (branched polymer). Amylose is usually dominant but high amylopectin varieties (mutant waxy maize) or subspecies (e.g. the glutinous rice, Oryza sativa var. glutinosa) exist. High amylose cultivars have been developed (Schwartz et al., 2009).
In addition to its major role as a source of energy in staple foods, starch has long been extracted by humans for food and non-food purposes. In ancient Egypt, an adhesive made from wheat starch was used to cement strips of papyrus. A complete procedure for starch production was given in a Roman treatise by Cato in 184 BCE (Schwartz et al., 2009). Today, the main starches are obtained from normal maize, waxy maize, high-amylose maize, cassava, potatoes and wheat. Rice, including waxy rice, peas, sago, oats, barley, rye, amaranth, sweet potatoes and other exotics are local sources of starch (Chiu et al., 2009).
Starches have many applications in food industries (e.g. confectionery, bakery, sweeteners, polyols, amino acids, brewing, distillery, soft drinks...), in non-food industries (e.g. textile, pharmaceuticals, paper...) and as a feedstock for the production of fuel grade ethanol (Crawshaw, 2004; Schwartz et al., 2009).
While valuable both as a source of energy and for their various physical functionalities, native and modified starches (see Processes below) are not widely used in animal feeding outside specialty feeds, such as pet food and milk replacers, since most feeds already contain grains. Pregelatinization makes starch readily soluble in cold water and suitable to replace lactose in calf milk replacers (Maningat et al., 2009). Starches play an important role in semi-purified diets used in animal feeding trials, where it is necessary, for instance, to adjust separately the energy and the protein content of the diet (Fuller, 2004). Pregelatinized starch and high amylose starch are particularly useful for their binding properties in the pelletization and extrusion processes (Maningat et al., 2009).