Research And Inhibitory Techniques Of Starch Retrogradation

Starch retrogradation is an unavoidable phenomenon that the gelatinized starch changes from an amorphous state to a crystalline one. There are several problems existing in this field of China, such as less retrogradation mechanism studied, unscientific measurements of retrogradation and single control technique for retrogradation in our food industries. In order to better deal with these issues, the major aim of this study was to explore the basic properties of the retrograded starch, the new determination methods and the novel inhibitory techniques for starch retrogradation.The ordering configuration of the retrograded starch was investigated using atomic force microscopy (AFM), molecular simulation (MS) and size-exclusion high performance liquid chromatography (SE-HPLC). The present data showed that the size of the short-term retrograded starch was significantly decreased with the increase of storage time. This decrease in size indicated that a disordered conformation of the starch fraction was transformed to an ordered one by the increase in Van der Waals (Vdw), hydrogen and electrostatic forces Furthermore, the change in molecular size was directly correlated to the retention time of amylose fraction. Mainly based on this correlation, a novel SE-HPLC method was developed to estimate the short-term retrogradation of rice starch. Compared to other well-established methods, the developed method was able to provide accurate short-term retrogradation data.The distribution of the“second”water molecules in the B-type retrograded starch was studied by solid-state NMR and molecular simulation. The results showed that the distribution direction of the“second”water molecules was opposite to the origin and the water molecules were circled with the radius of 0.39 nm. It was also found that the bound water content (Mb) of retrograded starch samples was significantly increased with the storage time. Based on the positive relationship between the bound water and the retrogradation, degree of starch retrogradation was determined by thermogravimetric analysis (TGA), and it was consistent with the data obtained from the DSC method. These findings suggest that the TGA as well as the DSC is able to provide potential data for evaluating the whole retrogradation of rice starch.The recrystallization kinetics and thermodynamic properties of retrograded rice starch were evaluated by a serial of thermal analysis techniques, including TGA, DTA and DSC. The results obtained from the first decomposition stage (30~190°C) indicated that the T5%, Td1 and Ea1 were significantly reduced for the retrograded samples (P≤0.05). Nevertheless, the storage of the gelatinized starches did not affect the Td2,ΔT2 and Ea2 during the second decomposition stage. In addition, the differential temperature (ΔT1) was significantly increased with the storage time (P≤0.05). Based on the measurement of theΔT1, retrogradation degree (DR) of rice starch was measured, and it was compared with the data collected from the DSC. The results indicated that there was no significant difference in DR values obtained from the two analytical methods. These findings suggest that the DTA technique is better suited for the measurement of the whole starch retrogradation than the DSC method. The distribution of iodine chains in the retrograded starch was investigated using solid-state NMR and molecular simulation. The present data showed that the resistance effect obviously occurred during the interaction of retrograded starch and iodine ions. The resistance resulted from the competition with the iodine chains of the starch helix and the hydrophobic core formed among the starch fractions. Furthermore, the extent of the resistance was selected as a parameter to explore the kinetics of starch recrystallization, indicating that the recrystallization data obtained were suitable for the Avrami equation (all correlation coefficients R > 0.99). These results suggest that the resistance extent is able to provide preliminary data for measuring the degree of starch retrogradation.The effect ofβ-cyclodextrin (β-CD) on short-term retrogradation of rice starch was investigated by DSC, molecular simulation, AFM and X-ray diffraction. Retrogradation of normal rice starch was reduced more by hydroxypropyl-β-CD andβ-CD than by glycerol monostearate (GMS). Differential scanning calorimetry (DSC) detected a potential amylose-β-CD non-inclusion complex formation. DSC data were analyzed using Avrami equation. The results also showed thatβ-CD significantly reduced the crystallizing rate (k) and increased the Avrami exponent (n) of amylose recrystallization (P<0.05). The molecular dynamics (MD) simulation indicated that the stability of the non-inclusion complex was primarily due to the non-bonded interactions, such as Van der Waals (Vdw), electrostatic force, and hydrogen bond formed in the presence ofβ-CD. Furthermore, the results demonstrated thatβ-CD competed with amylose to disrupt the formation of amylose-lipid complex and a potential amylose-β-CD-lipid complex was formed in the retrograded starch. The complex formation obviously generated the association of starch chains due to the short and fat aggregates observed using atomic force microscopy (AFM). These findings suggest that the formed amylose-β-CD-lipid complex was responsible for the inhibitory effect ofβ-CD on starch retrogradation.Retrogradation process of pressure-gelatinized rice starches was investigated and compared with the heat-gelatinized ones in this study. Our results showed that the retrogradation rate of normal rice starch gelatinized by high hydrostatic pressure (HHP) was slower than that by heat. Nevertheless, there was no difference in retrogradation rate for waxy rice starch gelatinized by the two treatments (P>0.05). The DSC data were further analyzed using the Avrami equation. The present results indicated that the pressure-gelatinized normal rice starch had a lower recrystallization rate (k) and a higher Avrami exponent (n) than the heat-gelatinized one, but the two treatments did not affect the k and n for waxy rice starch. In addition, the higher freezable water, the lower amylose leaching and the intact starch granules were observed only in the pressure-gelatinized normal rice starch. These findings suggest that the inhibitory mechanism of the HHP treatment on starch retrogradation is probably attributed to less broken granules and lower leached amylose.