Starch represents the single-largest source of calories consumed by humans and animals. It has functional capabilities as gums and gels, and in extruded foods provides texture and structure. Starch is primarily glucose in two principal polymers — amylose and amylopectin. Amylose is a linear helical chain, and amylopectin is highly branched which forms a double helix. In most starches, amylose is approximately 25% and amylopectin 75% of the molecule. These are arranged radially in layers forming tight bundles described as starch granules. The size and shape of the granules differ from one starch source to the next, as in small for rice and large for potato.
Raw starch is relatively insoluble in cold water and digestibility is low. To improve digestibility, heating in the presence of water leads to disruption in the order (crystalline structure) of the starch granule in a process known as gelatinization. The unfolding and swelling allows for the penetration of digestive enzymes that permit a higher proportion of the starch to be utilized by the animal. A “fully cooked” starch would have a rapid and complete digestion to glucose which can be seen as a spike in circulating glucose levels immediately following a meal.
