Modification of Starch Granules by Acid Hydrolysis

The D-glucose residues of amylose have been specifically oxidized at C-3 with phosphorus pentoxide in dimethylsulfoxide, followed by reduction with sodium borohydride, to produce D-allose residues in the amylose chain [45]. 

A hot-water-soluble starch was prepared by treatment of starch granules with 7.5% (w/v) hydrochloric acid in a water suspension for 1 week at 22-24 C, or for 

3 days at 40°C, followed by washing of the granules until they were free of acid [48]. The method is called the Lintner procedure and is the method currently used to produce commercial soluble starch. The product is highly heterogeneous and has a relatively high reducing value. 

Another method for producing soluble starches is the method reported by Small in which starch granules are refluxed in 95% ethanol containing 0.2-1.6% (w/v) hydrochloric acid for 6-15 min [49]. This method gives the maximum conversion of raw starch into soluble starch, with minimal production of low molecular weight dextrins. 

In further study of the treatment of starch granules in these alcohols with 0.36 and 6.0% (w/v) hydrochloric acid at 25 C, Fox and Robyt [51] reported the kinetics of the reaction (d.p. vs. time of reaction). It was found that different limiting d.p. values, different chain lengths, and different proportions of amylose and amylopectin were obtained by reaction in the four different alcohols and the two acid concentrations. The procedures create new kinds of soluble limit dextrins. 

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