Effect of starch granule structure, associated components and processing on nutritive value of cereal starch: A review

Starch is organized in concentric alternating semi-crystalline and amorphous layers in granules of various sizes within the endosperm. The amount of amylose in starch normally varies between 200 and 300 g/kg, but waxy cereals may contain negligible amounts and starch from high-amylose varieties may contain up to 700 g amylose/kg. High amylose content is associated with reduced digestibility. Fat and protein are found on the surface of starch granules, and these components may act as physical barriers to digestion. Heat treatment with sufficient water present will cause gelatinisation that will increase susceptibility for starch degradation in the digestive tract, although a linear relationship between extent of gelatinisation due to processing and digestibility has not been found. The low water content during feed processing limits the extent of gelatinisation, but gelatinisation temperature and extent of gelatinisation will be affected by properties of the starch, which in turn may affect digestibility. The effect of starch properties and feed processing on digestion in non-ruminant animals and ruminants are discussed.