Composition of Starch

Starch granules are composed of two different polysaccharides, amylopectin and amylose the former constitutes about 80 % of the most common starches. Separation of the two components can be achieved by selective precipitation involving the formation of an insoluble complex of amylose with polar organic substances. 

Amylose consists of linear chains, whereas amylopectin has a branched structure (Fig. 5). These chemical differences give the two substances different properties which contribute towards the distinctive characteristics of a starch from a particular plant origin. 

Amylose, although water soluble, gives an unstable solution which irreversibly precipitates. It is mainly responsible for the deep blue coloration given by starch and iodine. Solutions of amylopectin are relatively stable. The iodine-binding capacity, on the other hand, is very low. A small amount of covalently bound phosphate normally appears with starch but its exact location within the molecule is not known. 

Starch is extensively used due to its adsorbing properties. In dissolved form, it is used as a skin emollient and as an antidote for iodine poisoning. Other applications include the use as a tablet filler and binder and disintegrant. Sterilized starch is used as a lubricant for surgeon gloves. Unlike talc, it is completely adsorbed by body tissues. Soluble starch is prepared by treating commercial potato starch with dilute hydrochloric acid until it forms an almost clear solution in hot water. 

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Starch is a polysaccharide found in many plant species. Com and potatoes are two common sources of industrial starch. The composition of starch varies somewhat in terms of the amount of branching of the polymer chains (11). Its principal use as a flocculant is in the Bayer process for extracting aluminum from bauxite ore. The digestion of bauxite in sodium hydroxide solution produces a suspension of finely divided iron minerals and siUcates, called red mud, in a highly alkaline Hquor. Starch is used to settle the red mud so that relatively pure alumina can be produced from the clarified Hquor. It has been largely replaced by acryHc acid and acrylamide-based (11,12) polymers, although a number of plants stiH add some starch in addition to synthetic polymers to reduce the level of residual suspended soHds in the Hquor. Starch [9005-25-8] can be modified with various reagents to produce semisynthetic polymers. The principal one of these is cationic starch, which is used as a retention aid in paper production as a component of a dual system (13,14) or a microparticle system (15). 

An edible film should have good water vapor barrier properties (low or no water permeation and diffusion through film), which should not increase or increase very little with increasing relative vapor pressure (Lawton, 1996). Films should withstand mechanical stress and strain to such an extent that they do not break easily under a decent mechanical force (Talja et al, 2008). Thus, composition of starch-based films is an important factor influencing its barrier and mechanical properties. Also, starch-based edible films may have an impact on the sensory and textural characteristics of the food. 

A second very widely distributed polysaccharide is starch, which is stored in the seeds, roots, and fibers of plants as a food reserve — a potential source of glucose. The chemical composition of starch varies with the source, but in any one starch there are two structurally different polysaccharides. Both consist entirely of glucose units, but one is a linear structure (amylose) and the other is a branched structure (amylopectin). 

Bastioli et al.172 claimed expanded articles from extruded compositions of starch, mixtures of EAA and EVOH copolymers, and an inorganic carbonate. Typically, the synthetic copolymers comprised 20-40% of the composition. Preferred extrusion temperatures were in the range 180°C to 210°C. Extrusion of a typical blend in a single-screw extruder at a temperature of 180°C produced a closed cell foam with a density of approximately 1.2 lb/ft3 (19kg/m3). 

The blue reaction is very useful in determining the amylose-amylopectin composition of starch,69,196,277 and in controlling of the effect of mechano-chemical and enzymic treatment and fractionation of starch79,71,204,278-289... 

A composition of starch, protein, and water constitutes a patented floccu-lant.1031 Coated paper, suitable for printing, may be prepared by coating it with a starch-soybean protein complex generated in situ on the paper surface.1032 Starch-protein complexes are also patented as additives that increase baking capacity.1033 1037... 

There are also patents on compositions of starch with modified esterified, etherified, and cross-linked starch to produce sizes1061 and adhesives.1062-1064... 

Galliard, T. and Bowler, P. 1987. Morphology and composition of starch, in Starch Properties and Potential, Critical Reports on Applied Chemistry, ed. T. Galliard, Vol. 13, pp. 54-78, John Wiley and Sons, New York. 

Chapter 6. Besides strengthening the coverage on dissolved-polymer gels, a section was added on theoretical treatment of starch gels as composites of starch granules in an amylose matrix. 

Structure and Composition of Starch.—Starch grains vary in shape from spheroidal to oval to chonchoidal to polygonal. They... 

Composition of starch grannies from ten piant sources... 

The all-important problem of stability was receiving further attention in the United States of America during this pre-World War I period. J. B. Bronstein took out a number of U. S. patents covering the stabilization of starch nitrate with borates, soda ash, lime, and the like. His contributions to the U. S. patent literature, for the purpose of improved stabilization treatments and for the increased efficiency of explosive compositions of starch nitrate, extended from 1907-26 and J. B. Bronstein, Jr., was granted a patent in 1939 for improving colloidal compositions of starch nitrate. 

A year later, Olsen patented a blasting composition of starch nitrate and a smokeless propellant. 

In 1942, U. S. patents were issued to still another of the Trojan group, W. Bowlby, for lacquer compositions of starch nitrate it has been unsuccessful in this use, however. 

Common natural starch contains less of amylose than the amylopectin one, and 3-25% of the former is wrapped within a framework of the latter. Composition of starches from different plants with respect to the above two classes are shown in Table 5.23b. 

High amylose (ca. 60-85% amylose) pea starch (HAP) was obtained from Stauderer (Germany) with a composition of starch 80% and protein ca. 1%. Normal yellow smooth pea starch (ca. 35% amylose STL) was purchased from Pelmolen (The Netherlands). The composition was starch 84% and protein ca. 5%. Water (W) and glycerol (G) were used as plasticizers. Waxy com (Amioca, WCN) and potato starch (Farina, PN) were obtained from National Starch and Avebe, respectively. 

T. Galliard and P. Bowler, "Morphology and composition of starch," in T. Galliard ed.. Starch Properties and Potential, 1st Edition, John Wiley Sons, New York, Chap. 3, pp. 55-78,1987. 

Guan, J., and s Hanna, M. A.(2004). Functional properties of extruded foam composites of starch acetate and corn cob fiber. 19,... 

RouUly A., Rigal L., Gilbert R.G., Synthesis and properties of composites of starch and chemically modified natural rubber, Polymer, 45, 2004, 7813-7820. 

Reis, R. L., A. M. Cunha, and M. J. Bevis, Using Nonconventional Processing to Develop Anisotropic and Biodegradable Composites of Starch-Based Thermoplastics Reinforced with Bone-like Ceramics, Medical Plastics and Biomaterials, November 1997, available online at www.devicelink.com. 

One of the most abundant poljmieric materials from renewable resources is starch. While abundant and inexpensive, however, starch alone as a material does not offer satisfactory properties for many applications. Meanwhile, the synthetic biodegradable pol5miers with satisfactory properties are prohibitively expensive when compared to commodity non-biodegradable polymers. A common approach is to make blends/composites of starch and other biodegradable synthetic polymers to produce materials of satisfactory properties and a low overall cost. 

Fig. 19.9. Composition of starch syrups (acid hydrolysis). a Glucose, b maltose (disaccharide), c oligosaccharide (degree of polymerization DP = 3-7), d higher saccharides...

Reis, R. L., Cunha, A. M., and Bevis, M. J., 1997, Using nonconventional processing to develop anisotropic and biodegradable composites of starch-based thermoplastics reinforced with bone-like ceramics. Med. Plast. Biomater. 4 46-50. 

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