Polysaccharides starch chemistry

Cultures of B. subtilis were introduced into the stems of young potato plants by Suit and Hibbert104 in an attempt to bring about replacement of starch by another polysaccharide. Sections of some of the resulting potatoes gave little or no color with iodine, and were provisionally designated starchless potatoes. However, based on analogy with recent developments in starch chemistry, it seems probable that the starchless potato was free from amylose, and contained only amylopectin. 

So far, our study of organic chemistry has dealt mainly with rather small molecules, containing perhaps as many as 50 to 75 atoms. But there also exist enormous molecules called macronwlecules, which contain hundreds of thousands of atoms. Some of these are naturally occurring, and make up classes of compounds that are, quite literally, vital the polysaccharides starch and cellulose, which provide us with food, clothing, and shelter (Chap. 35) proteins, which constitute much of the animal body, hold it together, and run it (Chap. 36) and nucleic acids, which control heredity on the molecular level (Chap. 37). 

Fundamental concepts of starch chemistry provide an interpretation of its function and behavior in various food uses. The characteristics of modified starches depend on granule structure and on specific size and shape of the component molecules. Most native starches contain both linear and branched polysaccharides. The linear fraction is responsible for gel formation and for various retrogradation effects, the branched fraction for high colloidal stability and good suspending qualities. Starches are employed in the food industry as gel formers, thickening agents, and colloidal emulsifiers. Desired characteristics can frequently be enhanced by choice of an appropriate modified starch. The various food uses are individually discussed from the standpoint of molecular behavior and optimal types of modification. 

Being also a polysaccharide, the chemistry of starch (Figures 3.7 through 3.9) is often considered to parallel the chemistry of cellulose. Although this may not be entirely the case to the skilled biochemical investigator, it will suffice for the present text where the main point is to illustrate the complexity of the molecular entities that are postulated to have made some (perhaps significant) contributions to the plant debris, eventually forming coal (Francis, 1961 Van Krevelen, 1961). 

Polysaccharide synthesis is under enzymatic control, but does not occur from a template as in protein synthesis. For this reason, each molecule of a particular polysaccharide will have its own unique molecular weight. The molecular weight of a carbohydrate polymer is usually expressed as an average. Starch or cellulose chains, for example, may vary by several hundred thousand in their molecular weights between individual molecules. For an excellent review of carbohydrate chemistry, see Binkley (1988). 

Karl MyrbAck, Products of the Enzymic Degradation of Starch and Glycogen 252 M. Stacey and P. W. Kent, The Polysaccharides of Mycobacterium tuberculosis 311 R. U. Lemieux and M. L. Wolfrom, The Chemistry of Streptomycin. 337... 

Phenol-carbohydrate derivatives, in higher plants, 20, 371-408 Photochemistry, of carbohydrates, 18, 9-59 Physical chemistry, of carbohydrates, 15, 11-51 of starch, 11, 335-385 Physical properties, of solutions of polysaccharides, 18, 357-398... 

In 1945, Ken, who was now Lecturer at Bristol University, was again invited by Hirst to move with him to Manchester University, this time as Senior Lecturer in Organic Chemistry. Once more, it became necessary for Hirst to concentrate his efforts on University and Government committee work. Ken Jones, therefore, took charge of the carbohydrate-research group, and supervised the completion of the explosives work. During this interval, Ken enjoyed the able collaboration of Dr. T. G. Halsall in studies on the structures of starch, cellulose, and glycogen, and on the oxidation of carbohydrates by periodate. The close association of Ken with Professor Hirst, which continued at Manchester University until 1948, was a tremendously fruitful one over 50 joint publications resulted from their research on complex polysaccharides. 

Greenwood, C. T., Aspects of the Physical Chemistry of Starch, 11, 335-385 Greenwood, C. T., The Size and Shape of Some Polysaccharide Molecules, 7, 289-332 11, 385-393 Greenwood, C. T., The Thermal Degradation of Starch, 22,483-515 Greenwood, C. T., and Milne, E. A., Starch Degrading and Synthesizing Enzymes A Discussion of Their Properties and Action Pattern, 23, 281-366... 

The enzymes used for this type of digestion in Analytical Chemistry are mainly hydrolytic enzymes, the catalytic effect of which is based on the insertion of water at a specific bond of the substrate. The hydrolytic enzymes used in analytical applications include lipases (which hydrolyse fats into long-chain fatty acids and glycerol) amylases (which hydrolyse starch and glycogen to maltose and to residual polysaccharides) and proteases (which attack the peptide bonds of proteins and peptides themselves). 

The fractionation of starch has been the subject of many publications in the past as well as in the present. The literature of the last twenty years, especially, shows a rapid accumulation of articles on starch research this can be accounted for by at least three major influences. These are, first, K. H. Meyer s fundamental discovery that most native starches consist, to the extent of about 20 %, of an essentially linear polysaccharide, which he called amylose. Second, T. J. Schoch s equally important demonstration of the ability of amylose to form water-insoluble, complex compounds with minor proportions of higher alcohols. Third, the fast-growing interest which Industry takes in useful polymers. In view of the great successes of cellulose chemistry, amylose chemistry could at least be very promising. 

The field of monosaccharides, disaccharides and polysaccharids contains many industrial examples of semi-synthesis, which have entered chemical history, such the hydrolysis of starch to form D-glucose, the esterification of cellulose, the chemistry of rayon and, more recently, advances in the chemistry of carbohydrate surfactants (ref.83). 

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