Study On The Interaction Of Sweet Potato Amylose And Amylopectin During Retrogradation

Retrograded starch has the abilities of reducing blood pressure and maintaining the blood glucose concentration,as well as improving the digestive function of gastrointestinal track.And now it becomes one of the most important food sources for the persons who suffered from the kind of diseases.However,the productivity of sweet potato retrograded starch was quite low,which has greatly limited its production and application.Studies show that the amylose and amylopectin ingredients in sweet potato starch may act to each other and affect the yield of retrograded starch to an extent during retrogradation.In this paper,sweet potato amylose and amylopectin with relatively small molecular weight were prepared by multi-step separation and purification processes include wet heat treating under high pressure,amylase digestion,organic solvent precipitation.The obtained sweet potato amylose,amylopectin and the starch mixture were studied by Ultraviolet Spectroscopy,Infrared Spectroscopy,Scanning Electron Microscopy and X-ray diffraction analysis.Sedimentation property and freeze-thaw stability of the sweet potato starch were studied and described the retrogradation degree of starch.The results showed that the order of starch species that resist retrogradation was: amylopectin>starch mixture>amylose.Thermodynamic data of sweet potato amylose,amylopectin and their starch mixture were studied based on empirical model method in the solid-liquid phase equilibrium theory.The solubilities of sweet potato starch in pure water were determined with equilibrium method within the temperature range of 303.15 K~353.15 K.It was found that the solubility of sweet potato starch increased with temperature in water.The solubility order is: amylopectin>starch mixture>amylose.Three mathmatic models called “ideal solution equation”,“Apelblat equation” and “polynomial empirical equation” were used to calculate the solubility of the species.From the calculated average relative deviation,it can be seen that the solubility of sweet potato starch in water is more consistent with “ polynomial empirical equation”.Retrogradation kinetic data of sweet potato amylose,amylopectin and their starch mixture were studied by Avrami equation.The temperature-heat flow data of three kinds of sweet potato starch at different times and storage temperatures were determined by differential scanning calorimetry analysis.The results showed that the retrograded rate decreased at the sequence of amylose,starch mixture and the amylopectin.Under room temperature(variable temperature 7 ?~28 ?),4 ?,25 ?and 70 ?,Avrami equation indexes n for amylose were all less than 1,indicating simultaneous nucleation have occurred.The Avrami indexes n of amylopectin stored at 4 ?(retrograded 24 h)and 25 ?(retrograded 13 h)were both greater than 1,suggesting multiple nucleation existed.For mixture of amylose and amylopectin,multiple nucleation only happened at the temperature of 4 ?(retrograded 6 h).