Study On Effect Frozen Storage On Molecular Weight And Distribution, Chain Conformation And Aggregated State Structure Of Gluten

With the increasing market for frozen foods, the gluten quality during frozen storage hasattracted attention in food industry. In this dissertation, Wheat gluten was used as modelmaterials. The mechanism of induced by frozen storage was elucidated by exploring theeffects of frozen mode (frozen and freeze thaw cycles) and storage time on molecular weightsize and distribution, molecular chain structure (fractal dimensions, conformation, size andtopography), aggregated structure and thermodynamic behavior of wheat gluten andrheological properties of dough under different frozen mode and storage time on. We will usethose basic data to explore the relationship between the microstructure of gluten with differentsize scale (chain structure and aggregated structure) structure and properties changes duringfrozen storage, and further study quality of the product was developed during the frozenstorage which has great commercial benefits as it will provide a useful practical guideline tomanufacture dough products. The main research and results are as follows:1. Effect of frozen mode and storage time on molecular weight size and its distribution ofwheat glutenWheat gluten and its subunits were affects by different frozen mode and storage time onmolecular weight size, distribution, free amino groups content and free sulfhydryl groupscontent analyzed by SAXS, SEC MALLS, SDS PAGE and spectrophotometrically. Theresults indicated that the dilute acetic acid solution (8mg/mL) is a good solution, so avoidingthe influence of the solvent on the characterization of the solute. The mean molecular weightand weight average molecular weight of the gluten decreased with increasing frozen time. Inthe elution pattern of SEC, as the frozen storage time increasing, the retention time of thegluten is negatively delayed and the areas also decreased, compared with that of the controlgluten. There is a new absorption peak in the frozen stored samples, the area of the peakincreased with frozen storage time. It was clearly seen that no remarkable difference andrelative mobilities of band could be observed for wheat gluten subunits with or without frozenstorage. The free amino groups content changed few and the free sulfhydryl group content ofthe gluten increased with the frozen storage time, indicating that the depolymerization of thegluten during frozen storage was attributed to the breakage of disulfide bonds. 2. Effect of frozen mode and storage time on molecular chain structure (fractaldimensions, conformation, size and topography)The effects of frozen mode and storage time on gluten molecular chain structureexplored by SAXS, SEC MALLS and AFM. It was found that the gluten chain forming afibril like network. But the network was weakened and the fractal dimensions decreasedduring the frozen storage. The radius of gyration (Rg) was positively related to fractaldimensions of the gluten, indicating that the breakage of the gluten chain is one reason of thedecrease of Rg. The results also showed that the gluten dissolved in the50mM acetic acidappeared to be similar to quasi spherical of the chain conformation, but the change of thestructure did not show an obvious relationship with the storage time.3. Estimation of Mark-Houwink-Sakurada (MHS) equation parameters for gluten andeffect of the frozen mode and storage time on conformation of the chainFractional separation of gluten using the fast protein liquid chromatography (FPLC) anda numerical method for determination of MHS equation were studied. With1%SDS buffer assolvent, MHS equations for SDS soluble gluten (SDS S G) and SDS insoluble gluten(SDS IS G) proteins were established as:[η]=1.7459×102M0.6933=×2qM0.6933=×2M0.6933v1.737510MHSw1.667710w(SDS S G)[η]=7.5682×103M0.737230.737230.7372v=7.5682×10qMHSMw=7.2079×10Mw(SDS IS G)The value of α (0.6933and0.7372) suggested that in this solvent the gluten behaved like asemiflexible and a semistiff chain for the SDS S G and SDS IS G respectively. Establish theMHS equation for the frozen stored gluten. The results indicated that the conformation of theSDS S G was a semiflexible chain and more flexibility with the storage time, but theconformation of the SDS IS G changed few during the constant temperature frozen storage.In the freeze thaw cycles, the conformation of the SDS S G and the SDS IS G became moreflexibility with the storage time. The decrease of the Rgalso attribute to the change of thechain conformation. 4. Effect of frozen mode and storage time on aggregated structure and thermodynamicbehaviorThe hydration gluten, dry gluten and glutenin using the SEM, FIRT and TGA, and theeffects of frozen mode and storage time on aggregated structure and thermodynamic behaviorexplored. Microstructure of the frozen stored gluten had great change based on SEMobservation. In secondary structure, the hydration gluten had no change, but modification ledto increase in β sheet for the dry gluten. The decomposition temperature decreased during thefrozen storage led to the thermostability deteriorated, which was positively related to theweakened tendency of gluten network.5. Effect of frozen mode and storage time on rheological properties of doughThe gluten and AP flour using a Micro dough farinograph and TPA, and the effects offrozen mode and storage time on rheological and textural properties explored. The resultsindicated that the rheological and textural properties of the dough deteriorated with add thefrozen stored gluten. The hardness of the dough had positively related to the molecular weightof the additive of the gluten. This suggested that the molecular weight and the molecularchain were the decisive influencing the quality of the dough for frozen storage.