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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]. Treatment
of soluble starch or that with the addition of glycine with
high temperatures inhibits, to a high extent, enzymatic
hydrolysis [Kroh & Schumaher, 1996].
During heating of starch at high temperatures with or
without the addition of acid acting as a catalyst, starch
undergoes dextrinisation. Degree of starch depolymerization
proceeding during this treatment and properties of
dextrins formed depend on the botanical origin of starch
and dextrinization conditions, especially acidity and temperature.
Dextrins obtained under specified conditions
demonstrate the properties of resistant starch [Ohkuma
et al., 1990]. The resistance of the resultant dextrins to the
activity of amylolytic enzymes increases with a proceeding
degree of dextrinization and elongated time of the process
[Wang et al., 2001].
The resistance of chemically-modified starches to the
activity of amylolytic enzymes results from changes in the
composition and structure of starch particle proceeding
upon modification. As a result of chemical modification,
different substituents are incorporated into starch chains
and bind to glucose residues. Their presence and the resulting
spatial changes in the chain are likely to hinder the
arrangement of the enzyme next to starch, enabling its normal
activity. The resistance of products of starch thermal
depolymerization – dextrins – to enzymatic activity results
from changes in their structure, compared to starch. Upon
heating of starch, depolymerization, transglucosidation and
repolymerization proceed in the interior of its particles.
With elongation of the dextrinization process, an increase is
observed in the number of 1,3 and 1,2 linkages between glucoside
residues of resultant dextrins [Ohkuma et al., 1990].
The free glucose formed adheres randomly to the chain,
which results in the formation of different linkages between
glucoside residues in dextrin, including these that do not
occur in normal starch. These linkages cannot be disrupted
by amylolytic enzymes occurring in the gastrointestinal tract
of humans. Only glucoamylase has been claimed to be capable
of disrupting a-1,3-glycoside linkages.
Reduced digestibility of starch may also result from its
interactions with some substances, including i.a. lipid substances
penetrating into the interior of amylose helices.
Complexes of sago starch with monoglycerides of fatty acids
in starch paste demonstrate reduced susceptibility to the
activity of amylases [Cui & Oates, 1999]. The same phenomenon
is also observed in other compounds, e.g. some fatty
acids. Together with amylose chains, they form durable complexes
which do not undergo hydrolysis with amylases. Such
complexes are also formed at a temperature of 37°C. They
are also likely to form in the small intestine of humans where
fatty 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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