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Resistant starch IVType 4 resistant starch (RS 4) includes starch modifiedchemically or physically (mainly by thermal treatment), orwith both those treatments. Acetylated starch of papilionaceousplants is characterized by a relatively high degree ofresistance to the activity of amylolytic enzymes. Similarproperties are displayed by starch of papilionaceous plantsmodified by hydroxypropylation. Resistance of the above--mentioned starch preparations increases with an increasingdegree of substitution [Hoover & Zhou, 2003]. Hydroxypropyldistarch phosphate exhibits twofold lower susceptibilityto the activity of amylases compared to native starch.Some resistance to enzymatic activity is also demonstratedby acetylated distarch phosphate [Östergård et al., 1988].Resistance of starch increases with an increasing number ofits chemical modifications applied simultaneously [Wolfet al., 1999]. The properties of resistant starch are alsoobserved in monostarch phosphate, however in this case theresistance degree increases along with a degree of substitutionwith phosphoric acid (V) [Sitohy & Ramadan, 2001].A product of monostarch phosphate heating with glycine ischaracterised by substantially higher resistance to the activityof amylolytic enzymes than the monostarch phosphateitself [Mas³yk et al., 2003]. Heating of soluble starch saturatedwith iron (III) ions also decreases its susceptibility tothe enzymatic activity [Leszczyñski et al., 2003]. Treatmentof soluble starch or that with the addition of glycine withhigh temperatures inhibits, to a high extent, enzymatichydrolysis [Kroh & Schumaher, 1996].During heating of starch at high temperatures with orwithout the addition of acid acting as a catalyst, starchundergoes dextrinisation. Degree of starch depolymerizationproceeding during this treatment and properties ofdextrins formed depend on the botanical origin of starchand dextrinization conditions, especially acidity and temperature.Dextrins obtained under specified conditionsdemonstrate the properties of resistant starch [Ohkumaet al., 1990]. The resistance of the resultant dextrins to theactivity of amylolytic enzymes increases with a proceedingdegree of dextrinization and elongated time of the process[Wang et al., 2001].The resistance of chemically-modified starches to theactivity of amylolytic enzymes results from changes in thecomposition and structure of starch particle proceedingupon modification. As a result of chemical modification,different substituents are incorporated into starch chainsand bind to glucose residues. Their presence and the resultingspatial changes in the chain are likely to hinder thearrangement of the enzyme next to starch, enabling its normalactivity. The resistance of products of starch thermaldepolymerization – dextrins – to enzymatic activity resultsfrom changes in their structure, compared to starch. Uponheating of starch, depolymerization, transglucosidation andrepolymerization proceed in the interior of its particles.With elongation of the dextrinization process, an increase isobserved in the number of 1,3 and 1,2 linkages between glucosideresidues of resultant dextrins [Ohkuma et al., 1990].The free glucose formed adheres randomly to the chain,which results in the formation of different linkages betweenglucoside residues in dextrin, including these that do notoccur in normal starch. These linkages cannot be disruptedby amylolytic enzymes occurring in the gastrointestinal tractof humans. Only glucoamylase has been claimed to be capableof disrupting a-1,3-glycoside linkages.Reduced digestibility of starch may also result from itsinteractions with some substances, including i.a. lipid substancespenetrating into the interior of amylose helices.Complexes of sago starch with monoglycerides of fatty acidsin starch paste demonstrate reduced susceptibility to theactivity of amylases [Cui & Oates, 1999]. The same phenomenonis also observed in other compounds, e.g. some fattyacids. Together with amylose chains, they form durable complexeswhich do not undergo hydrolysis with amylases. Suchcomplexes are also formed at a temperature of 37°C. Theyare also likely to form in the small intestine of humans wherefatty acids, released from lipids under the influence of lipase,may complex with the products of partial starch hydrolysis,
thus increasing the amount of not-digested resistant starch
passing to the large bowel [Crowe et al., 2000].
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