Study On Improvement Of Gelation Behavior Of Tapioca Starch

In order to improve the structure,gel strength,elasticity and thermal stability of tapioca starch,it was modified by chemical modification and hydrocolloid-starch combinations in this paper.The changes of particle morphology,swelling ability,short-term retrogradation,gel stability and viscosity of tapioca starch during gelatinization were studied by various detection methods.This paper was on the basis of cross-linked tapioca starch,further explored the binding rules of konjac gum with different tapioca starches.The effect of different modification methods on the gel properties of tapioca starch was further and comprehensively investigated.The response surface methodology was used to optimize experimental conditions of cross-linked tapioca starch and showed that the optimal processing conditions were reaction time of 3 h,reaction temperature of 39.6 ?,the addition amount of sodium trimetaphosphate of 0.7%,pH of 10.23.The final viscosity increased by nearly 1.5 times compared with native tapioca starch.By measuring the properties of native tapioca starch and cross-linked tapioca starch,found that the polarization cross,particle morphology of cross-linked tapioca starch stayed the same with native starch.The thermal properties by differential scaning calorimetry showed the ?H first increased from 16.47 J/g to 18.40 J/g and then decreased to 17.17 J/g with increasing cross-linking degree.The vaules of final viscosity and setback had the same trend with ?H while the vaules of breakdown viscosity was decreased.The steady-state rheological properties showed tapioca starch pastes with different cross-linking degrees were pseudoplastic non-Newtonian fluid(T0>0,n<1).The dynamic rheological properties demonstrated that the storage modulus(G?)and loss modulus(G??)of the cross-linked tapioca starch gel were improved compared with native tapioca starch gel in the frequency region of 0.1~10 Hz.The G? of the proper cross-linked tapioca starch gel was increased,while tan? was decreased during the aging time for 2 h at 4 ?.Compared with native tapioca starch gel,the G? and G?? of cross-linked tapioca starch gel were improved during heating and cooling.The G? of the tapioca starch gel had increased rapidly with increasing cross-linking degree during cooling.On the basis of cross-linked starch,combined with the compounding technology of biological macromolecules,the optimized process conditions of different compound powders were studied by single factor and orthogonal experiments.The optimum preparation parameters of cross-linked tapioca starch-konjac gum mixed system were as follows: the concentration of alkali 1.7 mol/L,the addition amount of 0.6% konjac gum,reaction time of 3 h.The optimum preparation parameters of native tapioca starch-sodium trimetaphosphate-konjac gum mixed system were as follows: the concentration of alkali 1.7 mol/L,the addition amount of 0.4% konjac gum and 1% sodium trimetaphosphate,reaction time of 3 h.The optimum preparation parameters of cross-linked tapioca starch-sodium trimetaphosphate-konjac gum mixed system were as follows: the concentration of alkali 1.7 mol/L,the addition amount of 0.4% konjac gum and 0.25% sodium trimetaphosphate,reaction time of 3 h.The vaules of G? at 95 ? increased in the order cross-linked tapioca starch-sodium trimetaphosphate-konjac gum(1251.5 Pa)> native tapioca starch-sodium trimetaphosphate-konjac gum(1068.5 Pa)> cross-linked tapioca starch-konjac gum(910 Pa)> cross-linked tapioca starch(694 Pa)> native tapioca starch(192.5 Pa).By measuring the properties of 5 kinds of tapioca starches,found that the polarization cross,particle morphology,crystal type of modified tapioca starches stayed the same with native tapioca starch,but some starch granules in compound powders were coated by konjac gum or adhered to each other.Studied infrared spectra of samples,found a new peak in the compound powders of 900~1300 cm-1.With different modification methods,increased the freeze-thaw stability,vaules of final viscosity,setback,average particle size while the swelling capacity,transparency,breakdown,decomposition temperature were decreased compared with native tapioca starch.The thermal properties by DSC and TGA showed the weight loss and ?H of the compound powders were decreased compared with native tapioca starch and cross-linked tapioca starch while the vaules of(Tc-To)were increased.5 kinds of starch gels were pseudoplastic non-Newtonian fluid(T0>0,n<1)at different temperatures(25 ??50 ??75 ?).The dynamic rheological properties of all tapioca starches showed viscoelastic properties with G?>G??,exhibited viscoelastic solid characteristics.With the increasing of strain(20~100%),the G? of modified tapioca starches decreased mildly compared with the native tapioca starch.Konjac gum had synergistic effect on tapioca starch gel systems,intermolecular hydrogen bonds of compound powder were further strengthened,conducived to the formation of gel structure at 4 ?.The strength and elasticity of the compound gels were increased,and the binding forces between the starch molecules were strong enough to resist the strong destruction of the high temperature,thermal stability of starch gels improved significantly.Dependence of modulus on frequency and temperature became weak.