Melissa Fitzgerald, NSW Agriculture, Yanco, NSW, Australia
RICE: Chemistry and Technology, Third Edition
Starch is one of the most important agricultural products for the world's population. Currently, 2,050 million tonnes of starch each year are produced from cereals (Khush, 1997), and rice contributes significantly to that figure (Burrell, 2003). Food use accounts for most of the starch, insofar as it can represent up to 80% of daily calorific intake in some cultures (Burrell, 2003). Starch is also used in many nonfood applications, including adhesives, coatings, pharmaceuticals, fillers, viscosity modifiers, and a host of others. Each application requires particular properties of the starch, and the properties of starch are largely defined by the macro-, micro-, and ultrastructure of the starch.
Starch granules constitute approximately 90% of the dry weight of a milled rice grain. Starch is polyglucose, and the two types of glucose polymers that constitute starch are amylose and amylopectin. Starch determines the physical and cooking properties of rice grains, or at least contributes to them through interactions with other components of the rice endosperm (proteins, lipids, water) or through interactions with other ingredients used to process the rice. The ratio of amylose and amylopectin in the starch, the solubility of each, and the structure of each fraction all contribute to the performance of the rice grain. The synthesis and structure of starch has long been a mystery, but because of the evolution of technology over the past decade, knowledge of starch synthesis and structure has grown exponentially. This deeper understanding makes it a real possibility that starch structure can one day be manipulated to target starches for particular markets and applications and to assist in identifying novel and potential applications.