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On the basis of X-ray diffraction spectrum, three crystallinitytypes of starch are distinguished: A, B, and C.Starch polymorphism results from a different length of lateralamylopectin chains and from the degree of order ofdouble helices. In A-type starch, double helices of chains,usually 10–12 glucose residues in length, crystallizing in ahexagonal system, are densely packed, with a small share ofcrystallisation water (4 water particles per 12 glucoseresidues). The B-type crystals with a pseudo-hexagonal systemare formed by rather loosely arranged double helices ofchains, 13–18 glucose residues in length, with the share ofa considerable number of water particles (36 per 12 glucoseresidues), grouped mainly in the centre of the crystal “cell”.The C form is considered a mixture of A and B forms[Gernat et al., 1990]. Type A crystallinity appears in starchof multiple cereals (wheat, maize, oat, rice) and of someroot plants (tapioca, sweet potato, taro). Type B is typical ofroot and tuber-bearing plants (potato, jam) and some cereals(high-amylose: barley, maize, rice). Type C crystallinityhas been observed, among other, in a number of leguminousplants. In starch of different maize species, containingfrom 0% to 84% of amylose, an inverse correlation has beenobserved between amylose content and a degree of crystallinity.Low-amylose starches form crystalline structuresof chains with an average polymerization degree of 20 glucoseresidues, with short chains (10–13) predominating, andare characterised by a high degree of type A crystallinity.On the contrary, high-amylose starches with a low degree ofcrystallinity form type B crystals made of long chains with35 glucose residues on average. Along with increasingstarch hydratation (10–30%), its crystallinity is also observedto increase [Cheetham & Tao, 1998].In plant tissues starch occurs in the form of structurescomposed of a high number of particles. Those structures,called granules, demonstrate a less or more regular, plain orcomplex, variety-specific shape. Their size (average) fluctuates,depending i.a. on the botanical origin, from 0.5 µm foramaranth to over 100 µm for canna. The regularity of starchchain ordering in a granule is reflected by its properties,namely the above-mentioned X-ray spectrum and the phenomenonof anisotrophy. The latter consists in the appearanceof luminous granule sections in the polarised light inthe microscopic image, taking the shape of the MalteseCross.In the light passing under the microscope, spherical lamination– the so-called “growth layer” – can be observed onstarch granules. It results from different refraction of lightin alternating crystalline and amorphous layers. The granulesurface is characterised by the occurrence of numerousirregularities and pores of a different diameter and inside--granule depth [Juszczak et al., 2003a, 2003 b]. The granulesurface features are determined by the botanical origin ofstarch and, along with an increasing size of granules, theyaffect the specific surface area of starch. The specific surfacearea is diversified depending on the type of starch andranges from e.g. 0.243 m2/g in the case of potato starch granuleswith type B crystallinity to 0.687 m2/g in the case of typeA maize starch granules [Fortuna et al., 2000]. The specificsurface area of starch granules and pore volume are correlatedwith gelatinisation temperature and the viscosity ofpastes obtained [Fortuna et al., 2000]. The specific surfacearea of starch granules, as well as the number and size ofpores, are also linked with the ability of starch to adsorb differentsubstances, including protein compounds andenzymes, and with its susceptibility to the effects of multipleexternal factors
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