The Solidifying Process of Starch, Amylose and Amylopectin

Abstract

The process of the solidification from gelatinous state for starch, amylose and amylopectin was investigated. The persuit of the change of this process was carried out by measuring time dependence of relative rigidity at constant temperature with the method of torsional braid analysis. It was attempted to apply reaction kinetics to clarify the entire picture of this process. By assuming that formation of bond is proportional to the increase of rigidity, the relation between rel ative rigidity G_r and retardation time τ was derived, namely ln(G_r^∞-Gr)/(G_r^∞-1)=-t/?N. The above equation implies that plot of ln(G_r^∞-Gr)/(G_r^∞-1) vs. time t should be expressed with the linear relation. This plot in the solidifying process turned out to be represented with three straight lines possessing the different inclination. It was assumed that the first stage of the solidifying process results from entanglement accompanied by approach of molecular chain and the second stage results from formation of bond due to van der Waals force and the third stage results from formation of hydrogen bond . Retardation time τ of the second process (II) and the third process (III) was obtained by the inclination of the above plot. Moreover, the activation energy of the solidifying process was obtained by plot of retardation time τ vs. 1/T (T; absolute temperature). The values are 8.0 kcal/mol (II), 12.8 kcal/mol (III) for starch, 7.3 kcal/mol (II), 19.6 kcal/mol (III) for amylose and 8.9 kcal/mol (II), 6.6 kcal/mol (III) for amylopectin . Successively, by applying the Eyring's theory of rate process to this process, the values of free energy of activation ΔF^≠, enthalpy of activation Δ H^≠ and entropy of activation ΔS^≠ were calculated. On the other hand, by assuming that time-temperature superposition principle may be applied to the change of G_r in the solidifying process, the apparent activation energy was obtained by plot of shift factor a_Τ vs. 1/T. These values are approximately coincident with the values obtained by temperature dependence of retardation time.