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TYPES AND STRUCTURE OF RESISTANT STARCHConcept and classification of resistant starchAs a carbohydrate occurring in food products, especiallycereal- and potato-based ones, and in organs of sometropical plants, starch provides the organism with necessaryenergy approximating 4 kcal (16.7 kJ) per g. As a result ofthe activity of amylolytic enzymes of the gastrointestinaltract (also in vitro) starch undergoes hydrolysis. Hence it isregarded a compound rapidly and completely digested andabsorbed in the small intestine in the form of glucose beinga product of hydrolysis. It has been shown, however, that itonly refers to starch subjected to thermal treatment in anappropriate amount of water (i.e. in a gelatinised form) andconsumed immediately after being prepared. Also rawstarch of some plant species (e.g. cereals), occurring as nongelatinisedgranules, has been demonstrated to undergocomplete, although slow, digestion. Therefore starch hasbeen divided into: rapidly digestible starch (RDS) – degradedto glucose within 20 min upon enzymatic activity, andslowly digestible starch (SDS) degraded to glucose with thesuccessive 100 min [Englyst et al., 1992].Some part of consumed starch has been observed to beincompletely digested and in the intact form or as productsof its partial hydrolysis to escape the small intestine andenter the large bowel. This part of starch has been termed”resistant starch” (RS). It constitutes the differencebetween the amount of starch subjected to the activity of acomplex of amylolytic enzymes and the amount of glucose(as starch equivalent) produced as a result of hydrolysis withthose enzymes. By definition, resistant starch is the sum ofstarch and products of its degradation not absorbed in thesmall intestine of a healthy human.Resistant starch has been found to appear in four forms.The early classification involved only three forms of starch[Englyst & Cummings, 1987; Englyst et al., 1992]: RS 1 –physically inaccessible starch; RS 2 – starch of raw (non--gelatinised) granules of some plant species; RS 3 – retrogradedstarch.In successive years, those forms were supplemented withanother one [Eerlingen & Delcour, 1995; Brown, 1996;Haralampu, 2000], namely – RS 4 – chemically- or physically-modifiedstarch.
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