RESISTANT STARCH – CLASSIFICATION, STRUCTURE, PRODUCTION

Starch is a high-molecular carbohydrate composed of linear (amylose) and branched (amylopectin) chains of glucose residues. In water, at increased temperatures, it undergoes gelatinisation followed by amylase-induced hydrolysis. Owing to this, it is completely digested in the gas-trointestinal tract of humans. Also raw starch of some plant species, e.g. cereals, is subject to complete but slow digestion. In addition, starch may occur in the form incapable of enzymatic hydrolysis, referred to as “resistant starch ” (RS). Resistant starch is a sum of starch and products of its degradation undigested in the small intestine of humans. There are four types of resist-ant starch. Type I RS – physically unavailable starch. Amylolytic enzymes have no access to starch accumulated in undamaged plant cells as the gas-trointestinal tract lacks enzymes capable of degrading the components of plant cell walls. Type II RS – raw starch of some plant species, e.g. potato. Type III RS – retrograded starch, i.e. spontaneously- or artificially-precipitated from starch paste, occurring in the form of water-insoluble semi-crystalline structures. As a result of retrogradation, more thermostable structures are formed by amylose rather than by amylopectin. The amount of resistant starch produced this way increases along with the increasing amylose content of starch. Type IV RS – chemically- or physically-modified starch. Resistant starch has been reported to reduce the caloric value of food products and to decrease glucose level in blood. In the large intestine, it is fermented by gut-colonising bacteria. Products of its fermentation include gases and short-chain fatty acids – acetic, propionic and butyric