Starches alkaline degradation

The degrading effect of alkali has been known for some time. Schoch, Wilson and Hudson146 concluded, from the fact that methyl /3-maltoside is stable when heated in 0.1 M caustic soda for considerable periods of time, that alkaline degradation of starch occurs only through the reducing end... 

No dialdehyde groups are detectable in modified celluloses obtained by oxidation of cellulose with persulfate, hypobromite, hypochlorite, permanganate, nitric acid, or dichromate. " Alkaline-hypochlorite oxidized starches, which have already been partially degraded by alkali, are more resistant to alkaline degradation than are unmodified starches, and the alkali-lability slowly decreases with increasing oxidation because of the resulting oxidation of reducing ends."... 

Polysaccharides. See also. Carbohydrates, Cellulose, Dextran, Dextrins, Fructans, Glycogen, Glycosiduro-nic acids (poly-), Pectin materials, Starch, and Xylan, alkaline degradation of, 13,289-329 associated with wood cellulose, 10, 283-333... 

Starch derivatives may also undergo hydrolysis and degradation under alkaline conditions. The hydrolysis of the nitriles, amides, and esters resulting from the reaction of starch with corresponding vinyl monomers is obvious. Considerable attention has been paid to the alkaline degradation of starch dialdehyde. It de-polymerized readily supposedly as a result of -elimination at C-5, although such a questionable -elimination should not be facile).70... 

R. L. Whistler, P. K. Chang, and G. N. Richards, Alkaline degradation of periodate-oxidized starch, J. Am. Chem. Soc., 81 (1959) 3133-3136 Compare I.-L. Andresen, T. J. Painter, and O. Smidsrod, Concerning the effect of periodate oxidation upon the intrinsic viscosity of alginate,... 

The catalytic effect of the hydroxide ion would normally be represented as part of the reaction rate constant (k ) for each temperature, because catalyst concentration normally remains constant. However, in the case of alkaline degradation of starch or cellulose, organic acids are produced which are converted to their salts by the alkali present, thus reducing the hydroxide ion concentration. Therefore, it seemed that this degradation reaction could be represented by second-order kinetics, with the hydroxide ion concentration determined by the stoichiometry of conversion of starch or cellulose to organic acids. 

There has been increasing interest in these on account of their potential for the synthesis of valuable enzymes that include alkaline proteases and those that degrade starch and cellulose. Strains of Bacillus sp. have been most extensively examined (Horikoshi 1999). 

Desizing by chemical decomposition is applicable to starch-based sizes. Since starch and its hydrophilic derivatives are soluble in water, it might be assumed that a simple alkaline rinse with surfactant would be sufficient to effect removal from the fibre. As is also the case with some other size polymers, however, once the starch solution has dried to a film on the fibre surface it is much more difficult to effect rehydration and dissolution. Thus controlled chemical degradation is required to disintegrate and solubilise the size film without damaging the cellulosic fibre. Enzymatic, oxidative and hydrolytic degradation methods can be used. 

The desizing of water-soluble size polymers can be summarised as follows. Batchwise or continuous methods can be used in both cases an adequate supply of hot water is needed during the washing-off. Hot water and detergent are needed to remove polyfvinyl alcohol) or carboxymethylcellulose. The addition of alkali may be beneficial with carboxymethylcellulose. Alkali is essential with modified starches and acrylic acid copolymers. Polyfvinyl alcohol) can be degraded effectively by alkaline oxidation. 

The fractionation of acid- and alkali-treated starches has been reported,64 but the products are obviously degraded. Further work is, however, necessary on the use of alkaline solutions for fractionating starch. Pacsu10 maintains that the addition of an amylose precipitant to an alkaline dispersion... 

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