Study On The Mechanism Of Retrogradation And Lipids Inhibit Retrogradation Of Lotus Seed Starch

The seeds of lotus, which contain rich nutrition and have significant physiological activities, are widely used as food and traditional medicine. Therefore, it is an important link for industrial development by processing to improve its added value. Starch is the main component of lotus seed, high amylose content makes it easier to retrograde for lotus seed products. It seriously affect the qualities of lotus seed products after processing, when the hardness, texture, transparency, viscoelastic properties are changed significantly. The retrogradation of starch was gelatinized starch molecules from disorderly to orderly. When the temperature is dropped to a certain degree, because of the shortage of molecular thermal energy, the system of entirely gelatinized starch at a state of non-equilibrium thermodynamics, molecular chains are attracted and arranged by hydrogen bond, which reduces the enthalpy of the system, and,finally, the crystallization is formed.The aim of this research is to extract and purify the starch from Guangchang white lotus seed, then evaluate the quality characteristics of lotus seed starch. We study the crystallization and thermodynamic properties of the aging starch, and the effect of different water contents on retrogradation through XRD, DSC, MD simulation It could explain the mechanism of retrogradation of starch at microcosmic level. This study compared the effect of six lipids with different configurations(chain length, saturation, position of unsaturated bonds) on retrogradation of lotus seed starch, and discussed the effect of lipids on the crystallization and thermodynamic properties of retrograded starch. It could be shown the determinants to maintain the stability of starch-lipid complex and the mechanism that lipids could inhibit the retrogradation of starch at microcosmic level. Main results are shown as follows:1. To research the quality of Guangchang white lotus seed starch, we found that lotus seed starch granule was mostly elliptic spherical, particle size was smaller, and the crystal type is C-type with the crystallinity of 37.2%. The amylose content was 39.22%. The temperature of gelatinization was from 61.4℃ to 69.7℃ with the enthalpy of 6.6 J/g. The lotus seed starch had weak stabilities of swelling and freeze-thaw, but the settling capacity was starong, and it’s easy to retrograde.2. The crystal type of retrograded starch was B-type. The melting peak temperature(Tp) and conclusion temperature(Tc) of crystalline were decreased with the increase of water content. Water content is a significant factor to affect the retrogradation of starch, the aging of starch will be inhibited when the water content is too high or too low. It was the most easily recrystallized of lotus seed starch with a water content of 70%, and the degree of retrogradation was the highest. The changes of parameters of the molecular conformation, water diffusion coefficient, non-bonded interaction of aging models with different water contents were analyzed using molecular dynamic(MD) simulation method. It was shown that molecular structure of amylose with water content of 70% tended to be more orderly, and had strongest non-bonded interaction at microcosmic level.3. Lipid could maintain the spatial reticulated structure and water-holding capacity of starch gel, reduce the crystallinity of aging starch. When the adding lipid exceeded to a certain amount, it would weaken the effect of inhibitting retrogradation. The values of onset temperature, peak temperature, conclusion temperature, and enthalpy were decreased when added lipid into the gelatinized starch.When adding the same number of moles of lipid, the effect of GML on inhibiting retrogradation was the best.4. The hydrophobic ‘tail’ of a lipid molecule could enter into the internal helical space of a single amylose helix, and form the complex with amylose. The complex was shown V-type crystallinity. The results of MD simulation suggested that the stability of the complex depended on the non-bonded interaction between amylose and lipid. The stability of the complex was higher when the length of lipid chain was longer, the unsaturation was lower, and position of unsaturated bond was farther with the polar head. As a result, amylose-GMS complex had the highest stability.