Inhibition Of Soluble Soybean Polysaccharides On Starch Retrogradation And Influencing Factors

China is a large agricultural producer and food importer,and the staple foods are mainly rice and noodles.Compared with bread,cooked rice and noodles are more difficult to be stored due to their high moisture content and simple components.Therefore,study on the retrogradation of rice and noodle has been a key problem.Recently,soluble soybean polysaccharide(SSPS),a kind of food hydrocolloid,has been found to have anti-retrogradation ability on starch.In Japan,SSPS has been widely applied to rice and noodle products to maintain the soft texture.However,there are many inconsistencies in the reported results of the anti-retrogradation ability of SSPS,and its mechanism and the influencing factors are still not clear.To address these problems,this thesis thoroughly studied the influencing factors on the anti-retrogradation ability of SSPS on starch,such as external factors-moisture content and SSPS concentration,internal factors-the ratio of amylose content to amylopectin content of starch(AM/AP ratio),the structure of starch granules from different sources,and the structural factors of molecular weight(Mw)and degree of esterification(DE)of SSPS.Moreover,the mechanism of anti-retrogradation ability was discussed,and applied and verified the results in cooked noodles preliminarily.The main research contents and results were presented as follows.Firstly,the effects of SSPS on the inhibition of native and waxy maize starch with different concentrations of SSPS(0.5%,1%,2%,4%)at the moisture contents of 55%and 90%were investigated.Low-field nuclear magnetic resonance(LF-NMR)was used to study the water distribution of starch gels,and the effects of SSPS on the pasting,retrogradation and textural properties of starch were investigated by X-ray diffraction(XRD),rapid viscosity analysis(RVA),confocal laser scanning microscopy(CLSM)and texture profile analysis(TPA).PVA results suggested that SSPS could reduce the pasting viscosities of both starches.LF-NMR results illustrated that 4%SSPS had the best binding ability of dominating water in all starch systems.CLSM results showed that SSPS coated the starch granules,and XRD results confirmed that SSPS provided better anti-retrogradation ability at high moisture content(90%),while it only worked at high concentration(4%)at low moisture content.In summary,the results above indicated that SSPS could inhibit starch retrogradation at high moisture content(90%),high SSPS concentration(4%),and high AM/AP ratio.In order to investigate the effect of different starch types on the anti-retrogradation effect of SSPS,four types of typical starches(maize starch,wheat starch,rice starch and tapioca starch)with different AM/AP ratios and the structures of starch granules were selected to investigate the pasting,retrogradation and textural properties of starch at 90%moisture content and 4%SSPS concentration.The RVA,LF-NMR,XRD and TPA results suggested that 4%SSPS solutions could inhibit retrogradation of maize and wheat starches,while accelerated the retrogradation of tapioca starch.It exerted almost no effect on rice starch.In summary,the results above suggested that the different starch types affect the anti-retrogradation effect of SSPS,and starch with high AM/AP ratio and porous granule structures was more favorable for SSPS to interact with it and inhibit retrogradation,and the electrostatic interaction between the particles with the same kind of charge might inhibit the anti-retrogradation effect of SSPS.Based on the studies above,wheat starch was selected due to its practicability and the good reaction on the anti-retrogradation effect of SSPS.The aim of this part was to investigate the effects of structural elements such as Mw and degree of esterification DE of SSPS on starch pasting and retrogradation characteristics at 90%moisture content and 4%SSPS concentration.The RVA,water holding capacity of gels and LF-NMR results indicated that the structure of SSPS influenced its hydrophilic ability,and the SSPS with high Mw had weak water binding ability,while the SSPS with medium Mw could maintain enough hydrophilic groups on the main chain,and the SSPS with lower DE had better water binding ability.The XRD and TPA results confirmed that the softer the gel texture after 14-day storage,the lower the relative crystallinity it was.In summary,SSPS with medium Mw and low DE had the best anti-retrogradation effect,while SSPS with high Mw and high DE performed the worst.Overall,SSPS with medium Mw(70×10~4～80×10~4 Da)and low DE(20)performed the best in anti-retrogradation.The mechanism of the anti-retrogradation effect of SSPS was to influence pasting,which mainly depended on the control of water and interaction with starch molecules.Finally,in order to verify the applicability of SSPS,the SSPS with medium Mw and low DE which had the best anti-retrogradation effect in the previous section was applied to two cooked noodle systems:the commercial wheat flour group and the wheat starch-gluten recombined flour group.Glyceryl monostearate(GM)and guar gum(GG)were selected as references.The storage time was 0 d to 90 d.XRD result indicated that SSPS and GM were better than GG in inhibiting retrogradation of cooked noodles.The result of LF-NMR showed that SSPS was the most effective inhibitor in inhibiting water precipitation from cooked noodles during long-term storage.The noodles with SSPS showed the best sensory quality.Combining above results and the cooking quality,textural properties and TGA results,at the maximum dose of the national standard,the SSPS with medium Mw and low DE could improve the cooking and textural qualities,thermal stability of noodles,and also inhibit retrogradation.