| Summary: | 碩士 === 輔仁大學 === 食品營養學系 === 84 ===
It is a common practice to add emulsifiers to retard the retrogradation processes of foods containing starch. An inclusion complex was found after annealing the mixture of defatted TNuS19 rice starch with a saturated amount of lauryl alcohol. THe differential scanning calorimeter (DSC) was used to analyze the decreases in the retrogradation rate constants of TNuS19 components involved in the complex formation. 1H nuclear magnetic resonance (1H NMR) spectroscopy was adopted to investigate the changes in hydration during the retrogradation of the TNuS19. The Avrami equation was further used to evaluate the retrogradation kinetics of TNuS19 and its components. There are two parameters in the Avrami equation, one is the mode of nucleation, noted as n, and the other is the retrogradation rate constant, k. The n values in the two control samples, TNuS19 and partially purified TNuS19 were respectively 0.542 and 0.514 which were smaller than those of the lauryl alcohol treated samples (0.726 and 0.862). This implied that an addition of lauryl alcohol into the controls would change the modes of nucleation and decrease their retrogradation rate constants from 0.827d-n and 0.834d-n to 0.396d-n and 0.392d-n respectively. Consequently, the order of retrogradation rates was as follows, partially purified TNuS19>TNuS19>TNuS19> partially purified TNuS19-lauryl alcolhol complex>TNuS19-lauryl alcohol complex.
It was reported that amylose, amylopectin and their complexes would independently proceed recrystallization during aging. Based on the assumption, the calculated limiting enthalpies of complexes of amylose and amylopectin were respectively 3.82 J/g and 2.72 J/g which were smaller than those for the controls ( 6.23 J/g and 3.44 J/g). The n values of amylose and amylopectin (0.452 and 0.584) were different from those of the treated (1.755 and 0.498). A higher degree of change in the nucleation mode was observed for the treated amylose than that for the treated amylopectin. The k values of amylose and amylopectin were 0.826d-n and 0.852d-n respectively, and decreased to 0.206d-n and 0.423d-n after the complex formation. Overall, the order of retrogradation rates was as follows, amylose>amylose>amylopectin>amylose-lauryl alcohol complex>amylopectin-lauryl alcohol complex.
Based on the standard chemical shift of 1H in D2O, the peaks in 1H NMR spectrum were observed at 3.6, 4.6 and 5.1 ppm for both of the retrograded TNuS19 and its corresponding complexes. The peak at 4.7 ppm was formed and increased as the retrogradation proceeded. The peak at 4.6 ppm was due to the strong hydrogen bounding existed between the free HOD and the hydroxyl groups on C2, C3, C6 of glucose in the gelatinized starch. They belong to the category of the bound water or the entrapped water. As the starch retrogradation proceeded, part of the above bound water was gradually released and more inter- or intra-starch hydrogen bondings were formed. Thus the hydration state of the starch was gradually changed during the recrystallization process. In another words, HOD nearby starch molecules will change from its initial immobilized phase (bound water) to a mobile phase (free water) during retrogradation. Threrfore, the peak at 4.7 ppm was observed during retrogradation. Experimental data also implied that the contribution of the peak at 4.7ppm was mostly from the recrystallized amylose, but not from the retrograded amylopectin. A lower increase rate in peak area at 4.7 ppm was found in the treated TNuS19. This is inferred that the changes in hydration states of TNuS 19 before and after retrogradation was different from those with lauryl alcohol added Based on the Avrami equation, n values of the control and the treated sample were 0.542 and 0.726 respectively, the retrogradation ate constant of TNuS19 was reduced from 0.1329d-n to 0.0516d-n when adding lauryl alcohol. When n=1, the retrogradation rate constant of the treated TNuS19 (0.0226d-n) was smaller than that of the control (0.514d-n). 1H NMR spectroscopy can be used to evaluate the change in hydration phenomena, and the retardation effect of lauryl alcohol on the retrogradation of TNuS19.
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