Selection Of Effective Solvent For Starch And Optimization Of The Method For Amylopectin Branching Structure

Research on physical and chemical structure of starch and establishing relationship between their fine structure and functional properties are essential theoretical basis to develop and utilize starch. But there are still many problems unsolved in analyzing and determining the fine structure of starch. This research chose representative rice and corn starches as research materials. The effective solvent for starch was chosen at first, and then we established accurate methods for determining the starch Mw, debranching the starch in organic solvent and determining the amylose content, so we could provide foundational support for analyzing the starch fine structure comprehensively.Solubility Index was used as the criterion to determine the most effective solvent for starch by dispersing four kinds of starches with different amylose content in several different solvents. The result showed:Solubility Index of the corn starches dispersed in 50mM NaNO3/DMSO, 60μl EtOH/DMSO and 50mM LiBr/DMSO was the largest,50mM NaNO3/DMSO was the best solvent for corn starches achieved 100% solubility; Rice starch also had the best solubility in these three solvents,50mM LiBr/DMSO was the best solvent for rice starch achieved 83.5 % solubility; Water was not a good solubilizer for the starch dispersed in DMSO; Using the organic system of HPSEC-MALLS-RI we further determined the starches molecular weight and molecular rotation radius which were dispersed in different solvents, the result showed the starch Mw and RMS were lower when dispersed in 50mM NaNO3/DMSO and 50mM LiBr/DMSO than in other solvents. So we could infer that these two solvents are effective solvents for analyzing starch structure at the same dissolved condition.Amylose and long branching chain in amylopectin were easy to crystallize after debranching in the aqueous phase, so it could cause the deviation by using HPSEC to determinate the starch molecular weight. In view of the fact discussed above, we established the method of debranching starch in organic solvent. We debranched the starch simple dispersed in different ratios of DMSO/H2O with the same amount of isoamylase addition, and the enzyme activity of isoamylase in a series of organic solvents was investigated. 30%DMSO was chosen as the organic solvent for debranching the starch. Using HPSEC to investigate the stability of debranched starch in water and 30%DMSO, the result showed that debranched starch was more stable in organic phase (30%DMSO) than in water.Amylose content of a series of rice starches were obtained by iodine method and Con A method, the result of iodine method was higher than Con A method. Through analyzing the relationship between the differences of amylose content obtained by these two methods and the long branching chain in amylopectin, we could conclude that the molecular weight and amount of branched chains in amylopectin have effects on the result of iodine method. The analysis system of HPSEC-MALLS-RI-Iodine hybrid reactor-UV detector was built up to determine the molecular weight of the debranched starch and the colour of iodine simultaneously. The result showed:in the same weight of starch, the ability to make the iodine blue decreased with the decrease of molecular weight of the long branching chain in amylopectin.