Starch and dextrin

Polysaccharides are condensation products of more than ten monosaccharide units examples are the starches and dextrins, which may be linear or branched polymers. Polysaccharides are sometimes classified as hexosans or pentosans, depending upon the identity of the constituent monosaccharides. 

Musculus and Meyer (12) measured the diffusion rates of some starches and dextrins in 1881. The work was designed to determine the relationship of these "isomeric or polymeric" forms to the simple sugars from which they were formed. They concluded that dextrin molecules must be much larger than those of the sugars. This work, however, preceeded Raoult s (13) development of the cryoscopic technique for the determination of the molecular weights of dissolved substances, and van t Hoff s (14) formulation of the solution laws. Further, since the vapor density method was obviously inapplicable, it was not possible for them to actually determine the degree of polymerization. 

Fio. 8.—Relation between Consumption of Sodium Hydroxide and Concentration of Carbohydrate m Aqueous Solution.1 (Concentration of polysaccharides is expressed in mole of n-glucose residue per liter of solution. Initial concentration of sodium hydroxide is 0.25 M. mole of sodium hydroxide consumed per mole of carbohydrate. Carbohydrates D-glucose O, D-fructose , sucrose X, lactose , maltose , starch , and dextrin A.)... 

Extraneous Organic Matter.—The presence of starch and dextrin may be recognised in the manner indicated for dyewood extracts. 

Often interfaces and colloids are discussed together. Colloids are disperse systems, in which one phase has dimensions in the order of 1 nm to 1 pm (see Fig. 1.1). The word colloid comes from the Greek word for glue and has been used the first time in 1861 by Graham1. He applied it to materials which seemed to dissolve but were not able to penetrate a membrane, such as albumin, starch, and dextrin. A dispersion is a two-phase system which is uniform on the macroscopic but not on the microscopic scale. It consists of grains or droplets of one phase in a matrix of the other phase. 

Cunningham et al.199-203 investigated the use of starches and dextrins as extenders for polyurethane foams. Starch generally had little effect on the foam density, while compressive strength moderately decreased with increasing starch content. Hydrophilic foams prepared using starch were suggested to have useful horticultural... 

Polysaccharides, including starches and dextrins, have been shown to reduce the volatility of aroma compounds, such as limonene, isoamyl acetate, ethyl hexanoate and beta-ionones.237... 

Anionic graft-polymerization of paraformaldehyde onto starch and dextrin has been effected in methyl sulfoxide solution, polymerization being initiated by the carbohydrate potassium alcoholate formed from the reaction of the carbohydrate with naphthalene potassium, a metallation procedure not previously described for carbohydrates.220... 

As I have already indicated, the polymeric carbohydrate materials available from natural sources include gums, starch and dextrins, cellulose, hemicellulose, chitin, and bacterial polysaccharides. 

Gums. Gums are hydrophobic or hydrophilic polysaccharides derived from plants or microorganisms that upon dispersing in either hot or cold water produce viscous mixtures or solutions (i.e., gels (1)). As used in the modern sense, the term gum includes any water-soluble or water-swellable polysaccharide or its derivative. This includes starch and dextrins and various derivatives of cellulose. The latter, however, are considered separately. 

Starch and Dextrins. Starch is a readily available mixture of polysaccharides. Starchy foods have been an important component of the human diet from prehistoric times to the present day. It is not surprising, therefore, that very practical uses for starch products developed very early and have continued throughout human history. Today, starch has a number of applications not only in the food industry but in other industries as well. In addition to its use in food, starch is also a source of chemicals (41) and sweeteners (42) and is used extensively in the paper industry (43-45) as a sizing agent and an adhesive. 

The utilization of starch as an adhesive can be traced at least to 3,500-4,000 B.C., when it was used by the Egyptians to bond papyrus strips. Today, starch and dextrins derived from starch find a variety of applications in adhesives (46). Dr. H. M. Kennedy of Grain Processing Corporation presents a detailed overview of the use of starch and dextrins in Chapter 23. 

Rudley, J. A. Adhesives from Starch and Dextrin, in Industrial Uses for Starch and its Derivatives, Applied Science, London. 1976, Chapter 1, 1-50. 

Despite present trends toward use of synthetic polymers developed over the last 10 or 20 years, starches are still being widely used as an adhesive in such applications as the production of paper and paperboard products, warp sizing, and bonding charcoal briquettes. Because of a unique combination of properties and low cost, these adhesives are almost impossible to exclude from many applications, especially those involving the use of hot paste (size) for anchoring fibers. For starch molecules to act as an adhesive, they must be chemically or thermally hydrated. Then, their adhesive character is developed and modified in different ways by chemicals or other additives for different end uses. As renewable resources that are both economical and reliable, starch and dextrin are likely to continue to be significant factors in the adhesive market for many years. 

This chapter s purpose is to define these low profile markets where starches and dextrins are being used and to describe how the adhesive character of starch is developed in different ways for different end uses. 

In the past several years, between 100 and 150 million pounds of starches and dextrins have been used by the textile industry for weaving and finishing cloth, almost 85% of which is acid-modified and derivatized starches. Very little dextrin or unmodified starch is used in warp sizing. 

The amount of starch and dextrin sold to the other adhesive markets can be roughly estimated at from 200 to 300 million pounds. It may even be in excess of 300 million pounds due to the inexact reporting procedures for the many specific end uses that comprise this market area. 

In order to understand why the malt a-amylase acts so slowly on a normal hexaose (Fraction PDXII) we have tried to apply the Michaelis-Menten theory and have determined the affinity constants of the enzyme-substrate compounds. If the concentration of starch and dextrin are expressed as moles of maltose per liter we find the affinity constant, K, between malt a-amylase and starch to be about 200 and for /3-amylase about 170. The affinity constant a-amylase to a-dextrin is so small that no values could be obtained. The constant certainly is smaller than 12. Thus, it is clear that the slow action of the malt a-amylase on the dextrin is due to a very low affinity of the enzyme to the substrate. In other words, the enzyme can readily attach itself to a long chain, but only with difficulty to chains shorter than a certain value. In the dextrinization period of the action of the enzyme on starch, a mixture of a-dextrins is produced with an average chain length of about 7 units. It can be assumed, therefore, that the enzyme readily attaches itself to chains that contain more than about 8 units provided that the chains are normal and contain no branchings or other anomalies. When anomalies occur these... 

Amylodeztrin.— This is a carbohydrate intermediate in properties between starch and dextrin. It occurs in the form of small irregularly shaped granules, in Mace, that take on a reddish brown to reddish violet color with iodine solutions. 

Carbohydrates Simple sugars that are absorbed quickly in the form of dextrose, sucrose, and lactose. Starch and dextrin are also carbohydrates that may be included in the preparation. 

The main vegetable adhesives are based on starch and dextrine the latter is a modified form of starch. Each has wide applications. 

Clarase . [Solvay Enzymes] Alpha-amylase enzyme for hydrolysis of starch and dextrins. 

Analysis of bread dough before and after fermentation showed that the quantity of starch and dextrin suffered no loss. 

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