Crystallinity of starch, food composition, and digestibility of starch

Starch granules in their native state are insoluble and semi-crystalline. There are three forms of starch/amylopectin in nature: A, B, and C: in cereals (A), tubers and high amylose starches (B), and some varieties of peas and beans (C). Crystallinity and rate of starch hydrolysis depend on the plant species and growing conditions. The changes during food preparation include gelatinisation, the formation of amylose-lipids and amylose-protein complexes, and resistant starch (RS) origin. They are accompanied by changes from crystal to amorphous form and vice versa. Starch in human food is mostly rapidly or slowly digestible. Rapidly digestible starch is formed by gelatinisation, cooking extrusion, breaking down of starch granules, or hydrolysis to maltodextrins. By definition, RS is not digested in the small intestine. This review addresses the influences of biochemical processes in the human body on starch digestibility. It is strongly influenced by the degree of chewing, the activity of α-amylase in the intestine, and transit time through the stomach and small intestine. Resistant starch and endogenous intestinal mucus support the growth of specialist microbes in the large intestine that produce a variety of short-chain fatty acids, causing the perception of satiety, lowering pH, and inhibiting pathogens in the colon.