| Lotus seed is an important economic crop in Jiangxi Province. The cooking properties and taste value of lotus seeds will deteriorate significantly during storage. The aged seeds show significantly different from fresh seeds, the hardness increase, the viscosity decrease, which indicates that texture, components or other changes have taken place. Lotus seeds aging phenomenon seriously affected the economic industrial development. To understand the causes of the change, lotus seeds of different years from Guangchang were used as material to investigate the changes in quality and starch, lipid and protein.DSC and other means were used to measure the taste evaluation, pasting properties and functional properties. They are indicators of quality evaluations. There were significant differences among lotus seeds of different years. The taste value of the score went down, DSC curves of the Tp, Tc, and AH increased. The capacity, including water absorption, oil absorption, emulsion activity, foaming capacity and gelation properties of aging lotus seeds decreased remarkably compared with fresh seeds. The results showed that with prolonged of the storage time, aging did occure in lotus seeds, and affected the quality significantly.Amylose and amylopectin contents were determined by dual wavelength, the relative crystallinity of starch determined by x-diffraction. With storage time, the amylase increased significant, but the amylopectin decreased significantly, amylose /amylopectin ratio increased significantly, the crystallinity of starch decreased. The higher amylose contented, the lower of the relative crystallinity of starch. Aging may cause seeds amylose content changes, and then affected the crystal structure of starch granules and starch pasting properties, which reflect changes in quality seeds.The values of crude fat content and fatty acid in different were measured, the fatty acid composition of fat and the relative percentage changes determined by GC-MS. Crude fat content of seeds decreased, while the fatty acid value increased significantly. A downward trend of fatty acids could be detected. Linoleic acid, oleic acid, linolenic acid and other unsaturated fatty acids decreased significantly, saturated fatty acid content increased. In the one hand, free fatty acids combined with amylose, increased the difficulty of starch granules gelatinizing. On the other hand, a large proportion of unsaturated fatty acid oxidized, formed small molecule, such as aldehydes, ketones and other volatile compounds.Total protein, thiol and disulfide content, different rates of change in soluble protein extraction were investigated, soluble protein molecular weight changes were determined by SDS-PAGE. With the extension of storage time, lotus seeds had little change in the total protein content, and thiol content significantly reduced, while the disulfide content increased significant. A variety of soluble protein decreased the extraction rate dropped significantly. Numbers of the bands of soluble protein patterns in SDS-PAGE didn't changed, but the protein content of each band were reduced, and the low molecular weight and high molecular weight protein content decreased significantly. It can be inferred from the results, thiol oxidized disulfide bonds of protein, making the formation of small molecules crosslinked protein molecules, then increasing the intensity of the protein, reducing its binding capacity, and forming complexes with starch. All these reasons changed the quality of lotus seeds.All the results showed that the change of starch, lipid and protein content and structural, leading the quality change of lotus seeds. The main reason may involve in the change of amylase and amylopectin content, starch granules, lipid oxidation hydrolysis, protein thiol cross-linking disulfide, resulting in a decline in cooking quality of lotus seeds. This research could provide further direction and reference of aging mechanism for lotus seeds; provide a theoretical basis for the storage and preservation. |
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