Preparation,Characteristic Properties And Molecular Structures Of Three Amorphous Starches Of Different Shapes

Starch is a renewable resource which naturally exists in the granule form of semi-crystalline structure.Amorphous(non-crystalline)structure not only has a higher proportion than crystalline state in the native starch granules,but also is the primary aggregation structure of starch in the process of starch application and final products.Previous studies found that amorphous starches could take on three different shapes of gelatinized-like,granular-like and beaded-like,and the characteristic properties changed accordingly.However,the molecular structures basis for the characteristic properties change of different shapes three amorphous starches was not clear.Taking tubers,cereals and legumes amorphous starches as the research objects,the preparation methods of three amorphous starches of different shapes were established.Their crystallline properties were qualitatively and quantitatively analyzed by applying X-ray diffraction and differential scanning calorimetry,and their basic and characteristic properties(cold-water solubility,adsorption and enzymatic hydrolysis properties at room temperature)were tested.Meanwhile,their molecular structures(molecular weight,chain length distribution and chain conformation)were investigated by using high performance molecular sieve chromatography and high performance anion chromatography in order to construct the relationship between the characteristic properties change and molecular structures of amorphous starches.The main results and conclusions were as follows:1.The preparation methods of three amorphous starches of different shapes were established.Based on the pasting temperature of starch measured by rapid viscosity analyzer,the hydrothermal preparation methods of amorphous starches were established by changing the system treatment temperature.Meanwhile,their shapes changes were observed by using optical microscope and scanning electron microscope.X-ray diffraction and differential scanning calorimeter were used to analyze their crystalline structure.The results showed that the gelatinized amorphous starches were prepared by heating starch suspensions(6%)at 95?,and granular and beaded amorphous starches could be obtained after the treatment at a lower starch concentration(2%instead of 6%)and treatment temperature(0?5? and 5?10? lower than pasting temperature).The morphologies of granular amorphous starches were divided into three types:ghost-like,porous and honeycomb-like.The preparation temperatures of gelatinous,granular and beaded amorphous starches decreased in turn,and no organic reagents were used in their preparation processes.2.It was found that there were significant differences in the basic properties of three amorphous starches of different shapes.Amylose contents of gelatinous amorphous starches were similar to those of native starches(19.5%?33.3%);the contents of granular amorphous starches(13.7%?16.8%)were the lowest;and the contents of beaded amorphous starches(71.4%?99.6%)were the highest.According to the measurement results under the principle of pore adsorption,specific surface areas of gelatinous amorphous starches(0.503?0.776 m2/g)were 3?8 times those of native starches,and the specific surface areas of granular amorphous starches(0.359?0.668 m2/g)were 2?10 times those of native starches.According to the equivalent sphere theory,mean particle sizes of granular amorphous starches(29.8?154.2?m)were 2?3 times those of native starches.The amylopectin contents of beaded amorphous starches were the lowest,so the rate of aging was the fastest.3.It was found that there were significant differences in the characteristic properties of three amorphous starches of different shapes.Solubility of granular amorphous starches in cold-water were 78.5%?94.2%;gelatinous and beaded amorphous starches could not dissolve in cold-water,which were similar to those of native starches.In terms of adsorption characteristics at room temperature,water-and oil-adsorption capacities of granular amorphous starches were 52.3%?71.2%and 43.4%?64.3%,respectively,which were 2?3 times those of native starches;water-and oil-adsorption capacities of gelatinous and beaded amorphous starches were 1?2 times those of native starches.In terms of enzymolysis rate of ?-amylase at room temperature,enzymolysis rates of granular amorphous starches(56.5%?82.6%)were 4?7 times those of native starches;enzymolysis rates of gelatinous and beaded amorphous starches(0.9%?12.5%)were lower than those of native starches.The cold-water solubility,water-and oil-adsorption capacities and enzymolysis rates at room temperature of granular amorphous starches were the highest.4.It was found that there were differences in the molecular structures of three amorphous starches of different shapes.High performance molecular sieve chromatography elution profiles of gelatinous and granular amorphous starches showed two peaks corresponding to amylopectin and amylose,and their molecular weights were 2.7?8.7×107 and 3.1?8.1×105 g/mol,respectively,close to those of amylopectin and amylose of native starches;elution profiles of beaded amorphous starches showed only one peak,and their molecular weights were:amylose,1.8?5.7×105 g/mol,close to those of amylose of native starches.Chain distribution profiles of gelatinous amorphous starches were basically consistent with those of native starches,and their chain conformations were similar(random roil);the proportion of long side chains(DP?37)of granular amorphous starches increased by 1%?2%,and the chain conformation was globular shape;the proportion of short side chains(DP6?36)of beaded amorphous starches increased by 7%?10%,and the chain conformation was rigid rod-like.The molecular weights of amorphous starches were:gelatinous amorphous starches>granular amorphous starches>beaded amorphous starches,and their chain conformations were random coil,spherical and rod-like,respectively.5.The molecular structure basis of characteristic properties of three amorphous starches of different shapes was found.To sum up,the characteristic properties of amorphous starches were related to theirs shapes.The molecular weights of granular amorphous starches were similar to those of gelatinous amorphous starches,but the cold-water solubility and enzymolysis rates at room temperature of the former were obviously higher than those of the latter.The molecular weights of gelatinous and beaded amorphous starches were distinctively different,but they were insoluble in cold-water,and their enzymolysis rates at room temperature were lower than those of native starches.Therefore,the shapes could affect the macroscopic properties,and the difference of chain conformations was the major factor that determined the characteristic properties of amorphous starches.Gelatinous and beaded amorphous starches could be used as ingredients for health food with low glycemic index.Granular amorphous starches had more potential to be applied as throat lozenges basic materials.