Study On Retrogradation Behavior Of Starch By Asymmetrical Flow Field-flow Fractionation Coupled With Multiple Detectors

Starch is one of the most important natural renewable resources.It has been widely used in the food,paper,and biodegradable materials industries.The molecular weight and structure of starch are the most important factors affecting the performance of starch-based products.Starch gelatinization is a phase transition process that the starch granules undergo an order-disorder phase transitions.Upon cooling,the starch chains in the gelatinized paste reassociate and then lead to the formation of more ordered structure.These molecular interactions are collectively termed“retrogradation”.Starch retrogradation can positively affect the quality of starch products,such as appearance,texture,and taste.Retrograded starch is known as resistant starch(RS3)which increases the resistance of starch to digestive enzymes.Therefore,it is critical to study the molecular weight,structure and the retrogradation mechanism of starch.In this thesis,asymmetric flow field-flow fractionation(AF4)combined with multiangle light scattering(MALS)and differential refractive index(dRI)detectors(AF4-MALS-dRI)was employed for studying starch retrogradation.In the first part(i.e.,Chapter 2),in order to study the effect of gelatinization on starch retrogradation,native maize starch was dissolved with DMSO or NaOH.Attenuated total reflection flourier transformed infrared spectroscopy(ATR-FTIR),X-ray diffraction(XRD),differential scanning calorimetry(DSC),and scanning electron microscopy(SEM)were used to characterize the structure and the morphology of starch gel.AF4-MALS-dRI was used to characterize the weight-average molecular weight(M_w),radius of gyration(R_g),and hydrodynamic radius(R_h).The results show that the retrogradation extent of the DMSO-treated starch gel was more obvious compared with that of NaOH-treated starch gel stored at 4?for the same time.It was found that NaOH treatment led to starch degradation when gelatinized starch was stored at 70?.The results demonstrate that gelatination process plays an important role in starch retrogradation.The second part(i.e.,Chapter 3),the effect of storage temperature,storage time,amylose content,botanical origin,and salt on starch retrogradation was investigated by AF4-MALS-dRI.It was found that the rate of starch retrogradation stored at 4?was fast compared with storage at 25?and 70?,indicating that starch retrogradation is a temperature-dependent process.Moreover,the result shows that the apparent density of starch obtained at 4?was smallest,which may promote an inter-starch association.It was also found that a mixture of potato amylose and maize amylopectin stored at 25?led to starch degradation,especially for maize amlyopectin.Results indicate that starch retrogradation is a dynamic process in which aggregation and disassociation coexist.On the one hand,the presence of small amylose aggregates plays an important role in the starch retrogradation and degradation.On the other hand,the content of amylsoe and storage temperature can effectively control starch retrogradation process.In this thesis,AF4-MALS-dRI was used to study the influencing factors of starch retrogradation under natural conditions.AF4-MALS-dRI was proved to be a powerful tool for studying starch retrogradation behavior.The results obtained in this study can provide basic data support for starch-based food industry.