Natural Polymers: A Focus on Starch and its Properties

Biopolymers are naturally occurring polymers that are formed under natural conditions during the growth cycles of all organisms. They are formed within cells through complex metabolic processes. Biopolymers are also known as natural polymers, and the most interesting for materials applications are cellulose and starch. However, there is an increasing interest in more complex hydrocarbon polymers produced by bacteria and fungi, particularly in polysaccharides such as xanthene, curdlan, pullulan, and hyduromic acid.

Starch is a polymer of hexacarbon monosaccharide – D-glucose. It is extremely abundant in corn seeds, potato tubers, and the roots and stems of other plants. The D-glucose structure can exist both in open-chain and in ring forms, and the ring configuration is ascribed to D-glucopyranose. The pyranose ring is a more thermodynamically stable structure, and it constitutes the sugar structure in the solutions.

Starch is mainly composed of D-glucopyranosis polymers bound by α-1,4- and α-1,6-glycoside links. These links are formed between the first carbon atom (C1) of one molecule and the fourth (C4) or sixth (C6) of the second one. As the aldehyde group on one end of a starch polymer is always free, these starch polymers always possess at least one reducing tip. The other end of the polymer is an irreducible tip. Depending on the degree of polymer branching occurring in a starch molecule, there may be great numbers of irreducible tips. The formation of α-links in a starch molecule enables some parts of starch polymers to generate helix structures; this is determined by the orientations of hydroxy (–OH) groups on the first carbon atom (C1) and the pyranose ring. Studies on starch’s chemical properties and structure have established that it is composed of two components, both also polysaccharides: amylose (20–35%) and amylopectin. The ratio of these components varies, subject to the source of origin. Amylose is a linear polymer, whereas the amylopectin molecule is substantially bigger and branched. These structural differences cause marked differences in starch’s characteristics and functions.

Starch appears in plants as granules, which are reserve materials. The sizes, shapes, and structures of these granules depend on their sources of origin. Although the main components of all kinds of starch are the polymers amylose and amylopectin, there is considerable recorded diversity in the structures and characteristics of the natural starch granules. The granule diameters vary from under 1 µm up to over 100 µm, and their shapes may be regular (round, oval, angular) or totally irregular. For example, potato starch obtained from potato sprout tubers Solanum tuberosum L. has granules of varied size (from 10 up to 100 µm) and of different shapes (round, oval, oviform, oblong, shell-shaped, and other irregular forms).

Starch is employed in the cosmetics and pharmaceutical industries for producing dusting powders and powders and as a filler. In addition, it serves as a means to obtain glucose, ethyl alcohol, and dextrins, as well as for stiffening and binding in these industries. Wheat starch from wheat grains (Triticum vulgare Villars) exists as single granules of two types: large ovals of 15–45 µm in diameter and smaller, more rounded forms of 2–7 µm in diameter. This type of starch is applied as a neutral dusting powder or as an ingredient in pharmaceutical preparations. In some plants

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