Researches On The Preparation And Properties Of Oxidized Cross-linked Sweet Potato Starch

Applications of natural sweet potato starch are confined to a certain extent because of its poor colour and heat-resistance,relative weak acid-resistance and freeze-thaw stability.On the basis of comparing all the methods of preparing modified starch,the mixed anhydride of acetic anhydride and adipic acid was chosen as the cross-linking agent to react with sweet potato starch in hydro-solution after oxidized reaction.The oxidized cross-linked acetylated distarch adipate were prepared by oxidized cross-linked reactions.The granule structure,property of paste,chemical dynamics and applications in food of oxidized low cross-linked acetylated distarch adipate had been studied systematically in this dissertation.By experiments and research,comprehensive knowledge of characters of oxidized cross-linked acetylated distarch adipate and reaction mechanism of cross-linking reaction are attained.The results of this study are not only good for the expanding of application scope of sweet potato starch,but good for the promotion of modifying research of sweet potato starch as well.Main researches are as follows:(1)Taking into account the properties of sweet potato starch that polyphenoloxidase(PPO)could make the colour black,quatity declind and limit it's deep processing,H₂O₂ was used as oxidizing agent to prepare oxidized starch to increase the white degree and improve the properties and processing adaptability.The result indicated that the optimum technology is in pH10.5,H₂O₂4.5%, reaction temperature 35℃,time 3.5h..(2)Reaction dynamics of cross-linking reaction in water was studied to attain the factors of influencing cross-linking reaction and the relationship between them and to attain the optimum technology by experiment of central composite rotatable,that is cross-linking agent 4%,reaction temperature 48.4℃,pH9.84.(3)The properties of sweet potato starch and oxidized low cross-linked acetylated distarch adipate prepared by the optimum technology were deteminated separately.In modified starch paste,there are higher freeze-thaw stability,weeker flocculation and ageing tendency,stronger ageing resistance, lower viscosity and better acid resistance,shear resistance and enzyme hydrolysis resistance,but the alkali resistance is weaker.The result also was attained by DSC that the beginning temperature To,the peak temperature Tp,the termination temperature Tc and the gelatinization enthalpyâ–³H are higer then raw starch.(4)By FTIR spectra,the molecules of oxidized low cross-linked acetylated distarch adipate had been analysized.The new absorption peak of carbonyl group had been found in 1729cm^-1,by which the moleculer structure of oxidized low cross-linked acetylated distarch adipate had been proved.(5)By using polarized light microscope and X-ray diffraction apparatus,the structure of the grains of oxidized low cross-linked acetylated distarch adipate had been studied.The polarized light cross can be seen clearly,which proved that there isn't obviously change in the nonrandom structure of the grains.By X-ray diffraction analysis,the diffraction regions and intensity in peaks are same as raw starch,what can be concluded is that the cross-linked action between sweet potato starch and mixed anhydride is almost in fredom fields.(6)The changes on the surface of the oxidized low cross-linked acetylated distarch adipate through oxidized cross-linking reaction had been discovered.The cross-linking actions between mixed anhydride and starch in water act not only in the surface of grains,but in inner section because of the swell of the starch grains in surface.(7)The enfluence of modified sweet potato starch on ageing resistence in steamed-bread show that the steamed-bread added modified starch is of smooth surface,homogeneous stoma,higher elasticity and resistance and better ageing resistance as well,in which experienced the weight variation was weaker and the weight loss was less than parallel samples in preservation and 0.5%addition was proper.(8)The crack resistance of modified starch in quick-frozen dumpling had been analysized.With the increasing of modified starch addition,there were less and less cracks and nearly no crack in 6%and its intact rate had reached to 95%,which indicated that the oxidized low cross-linked sweet potato starch can make a good improvement to quick-frozen dumpling.