Application Of Asymmetrical Flow Field-flow Fractionation For Separation And Characterization Of Maize Starch

Starch is a renewable,degrable,derivable and non-toxic polysaccharide.It has been widely used in food engineering,environmental science,biomedicine.Starch is insoluble in cold water at room temperature,partially soluble in hot water.Dissolved starch is prone to retrogradation when temperature is lowered.It is reported that the solubility of starch affects the accurate characterization of starch particle size and M_w distribution,and starch degradation affects the texture,taste and hardness of starch products.Although,studies on starch dissolution and retrogradation have been reported,starch dissolution is still a challenge,and the mechanism of starch retrogradation is not yet clear.Therefore,this thesis carries out the following researchs:?1?Study on the dissolution and retrogradation behavior of maize starch based on asymmetric flow field-flow fractionation.?2?Development of ultrasound-assisted DMSO method for dissolution of maize starch.Maize starch is dissolved by sodium hydroxide?NaOH?together with carrier liquid or ultra-pure water.The carrier liquid consists of 5 mM NaNO₃ and 3 mM NaN₃.The dissolved maize starch was stored at 4?for different times.Asymmetric flow field-flow fractionation?AF4?coupled with multi-angle laser light scattering?MALS?and differential refractive index?dRI?detector?AF4-MALS-dRI?was employed to monitor the effect of NaNO₃ on the dissolution and retrogradation of maize starch.It was found that the NaOH-carrier-dissolved maize starch dissolved in a water bath at 75?for 2 h,and there was no obvious retrogradation at 4?storage different times,However,NaOH-water-dissolved maize starch was very sensitive to the water bath temperature.It can be dissolved in the water bath at 70?for 2 h.And an obvious retrogradation at 4?storage was observed.In addition,the ultrasound-assisted DMSO method for dissolution of maize starch was developed.Ultrasound-assisted DMSO-dissolved starch method has some advantages such as simple operation,short dissolution time,and environmentally firendly.In this study,the effect of ultrasonic time,ultrasonic power,DMSO dosage and water bath time on dissolution of maize starch was studied.Dissolved maize starch was separation and characterization by AF4-MALS-dRI and differential scanning calorimeter?DSC?.The repeatability and reproducibility of ultrasound-assisted DMSO-dissolved starch and AF4-MALS-dRI were studied.It was found that under the condition of ultrasonic time 2.5 min,ultrasonic power 80W,DMSO dosage 2 mL,heating time 30 min,maize starch was complete dissolution and did not degrade.The results showed that the ultrasound-assisted DMSO dissolution method and the AF4-MALS-dRI combination technique had good repeatability and reproducibility.The AF4-MALS-dRI was used to monitor the dissolution and retrogradation behavior of maize starch.AF4-MALS-dRI was proved to be a powerful tool of monitoring starch polysaccharides.The data obtain in this thesis would be valuable for the starch based industries.