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Resistant starch IIIType 3 resistant starch (RS 3) is a substance precipitatedfrom paste or starch gel in the retrogradation process.During starch gelatinisation, starchy substance partlydepolymerized as a result of temperature-water interactionpasses from swollen granules into solution, thus forminga colloidal water solution, called starch paste. At an appropriateconcentration (over 1.5% of amylose or over 10% ofamylopectin) and lowered temperature, the starch pasteundergoes gelatinisation which proceeds in two stages. Atthe first stage, phases are subject to separation, as a resultof which the solid phase of a polymer forms a net-like structurewhich binds the liquid phase in its meshes. At the secondstage, double helices of amylose are formed in the polymerphase. The amylose gel occurs as a microporousstructure made of threads, 10–30 nm in diameter. They arecomposed of joint segments of amylose chains, with a degreeof polymerization ranging from 26 to 73, appearing inthe form of double helices. Within a few hours of gel storage,the helices aggregate and form highly thermostable(dissolution temperature above 150°C) B-type crystallinestructures. Apart from those structures, gel structureincludes also amorphous phase made of loose amylosechains with the polymerization degree of 6–30 [Leloupet al., 1992a]. During gel treatment with amylolytic enzymes,the amorphous fraction undergoes hydrolysis and furtherordering of amylose chains proceeds, contrary to the crystallinefraction built of those chains, which remains resistantto the enzymatic activity [Colquhoun et al., 1995]. The formationof resistant starch III is affected by lipid substanceswhich occur in starch of numerous plants and form inclusivecomplexes with amylose, penetrating into its chains. Suchamylose does not bind into double helices which form crystallinestructures upon aggregation. Therefore, a lowernumber of insoluble crystallites of amylose are precipitatedin the retrogradation process, thus less resistant starch isproduced [Eerlingen et al., 1994].Amylopectin gels are also partly crystalline. Short outerbranch-points of amylopectin with a polymerization degreeof 14–20 link into crystalline structures, forming a net.Unlike amylose, the crystallisation of amylopectin proceedsvery slowly. The amylopectin crystalline structures are lessstable than those of amylose, which results from a limitedlength of their chains. Their dissolution temperature rangesfrom 55 to 70°C [Eerlingen & Delcour, 1995].The crystalline structures formed in starch pastes andgels, growing during storage – especially at lower temperatures,reveal resistance to the activity of amylolytic enzymes.Retrograded starch, precipitated from pastes or gels,demonstrates a semi-crystalline character and only its partundergoes enzymatic hydrolysis. Its major part behaves typicallyof starch resistant to the activity of amylolytic enzymes[Shin et al., 2003].Storage temperature of starch paste affects the amountand character of resistant starch formed. When paste isstored for several hours at a low temperature, more resistantstarch is formed than upon paste storage at high temperatures.Still, long storage of paste at a temperatureapproximating 100°C results in the formation of higheramounts of resistant starch than within the same time, butat lower temperatures [Eerlingen et al., 1993]. Resistantstarch formed at low temperatures demonstrates the B-typeof crystallinity, whereas that produced during starch pastestorage at the boiling temperature – the A-pattern of crystallinity[Shamai et al., 2003]. At low temperatures, majorpart of amylose is subject to retrogradation and precipitationfrom the solution, at higher temperatures thoseprocesses proceed only in its fractions with a low degree of
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