Study On Formation Mechanism And Physicochemical Characteristics Of A, B Type Starch Granules In Wheat Endosperm

Wheat is one of most important food crops in the world, yield and quality of which are suggested to have a role in international food supplies security and regional condition tranquilization. In China, wheat is the second large food crop just less than rice. With ever increasing standard of living of pepole and development of food industry, the quality requirement level for production of wheat is more and more strict. However, more scholars mainly concentrated on the research of wheat protein and amino acid in past a long period, and finally ignored the study of wheat starch. Starch accounted for 65%-70% weight in dry wheat grain, thus it was the main composition of wheat grain and was a more important quality character. Therefor, four wheat cultivars with different starch content were chosen for this research work and a series of modem detecting techniques were used to systemicly study the formation mechanism and physico-chemical characteristics of A, B type starch granules in wheat endosperm. These techniques included Sodium Dodecyl Sulphate Polyacrylamide Gel Electrophoresis (SDS-PAGE), Two-dimensional Gel Electrophoresis (2-DE), and Matrix-assisted Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI-TOF-MS) for the research of formation mechanism, whereas Scanning Electronic Microscope (SEM), Viscosity Amylograph (Brabender, Germany), Differential Scanning Calorimeter (DSC), Laser Particle Analyzer and X-ray Diffractometer (X-RD) etc for the research of physico-chemical characteristics to A, B type starch granules in wheat endosperm respectively. The major contents and results of this paper were as follows:1. Starch granule were isolated and purified from four wheat cultivars grain using macromethod and micromethod, and were tested by SEM. The results showed that the purity of A type starch granules ranged from 79.46% to 85.23%, which of B type starch granules ranged from 90.27% to 96.43% by using macromethod; if using micromethod, the purity of A type starch granules ranged from 92.68% to 96.70%, which of B type starch granules ranged from 96.48% to 99.00%.The effects of isolation and purification for A, B-type starch granule indicated significant level in macromethod, and distinct significant level in micromethod. In other words, the purity of A, B type starch granules with micromethod was higher than that of macromethod, but the ratio of A, B type starch granules with micromethod was more less than that of macromethod.2. The developing condition of starch granules in wheat endosperm were continuously observed with Scanning Electronic Microscope (SEM), and found that amyloplast and A type starch granules emerged at approximately 3 day post anthesis (DPA) and B type starch granules emerged at approximately 15 DPA. The amyloplast began to disappear from 9 DPA, but A and B type starch granules continuously grew till.wheat grain matured. Starch granule band protein (SGP) of wheat A, B type starch granules were separated and identified by Sodium Dodecyl Sulphate Polyacrylamide Gel Electrophoresis (SDS-PAGE), Two-dimensional Gel Electrophoresis (2-DE), and Matrix-assisted Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI-TOF-MS). The results showed that the reason why A type starch granules formation was that it had 3 sort of SGPs (SGP-145, SGP-150 and SGP-152), which could promote the biosynthesis of amylopectin, especially the degree of polymerization of chain length of amylopectin> 40(DP>40), and finally caused the formation of A type starch granules. The diameter of B type starch granules was less than 10μm, due to they lacked of such 3 SGPs.3. The natural ruptured side of kernel of different deveoping periods and the separated & purified A, B type starch granules of wheat endosperm in wheat were observed by Scanning Electron Micrograph (SEM). The results showed that wheat starch granules could be divided into A and B type by its diameter of 10μm, and could be divided into normal and abnormal by its shape. The shape of separated & purified A type starch granules was shell structure but the shape of most B type starch granules indicated spherical structure. The contents of amylose and amylopectin in A, B type starch granules of wheat endosperm of different developing periods were determined by AMYLOSE/AMYLOPECTIN ASSAY PROCEDURE, and the results indicated that the formation of amylose in starch granule of wheat endosperm was earlier than that of amylopectin, while the final content of amylopectin was much higher than that of amylose, and the amylopectin contents in A, B type starch granules had a positive correlation trend to total starch content.4. The swellings power of A, B type starch granules in matured wheat endosperm were measured according to method of McCormick, and the results showed that the swelling power of B-type starch granule was higher than that of A-type starch granule. Viscosity and thermal characteristics of A, B type starch granules of wheat were determined by Viscosity Amylograph (Brabender, Germany) and Differential Scanning Calorimeter (DSC). The results showed that the color of A, B type starch granules after cataplasm were sky blue, both the peak value of paste (PV) and the value of enthalpy change (△H) of B-type starch granule were higher than that of A-type starch granule.5. The size distribution of starch granules were determined using Laser Particle Analyzer and the crystalline properties of A, B type starch granules were determined by X-ray Diffractometer (X-RD) The results of size distribution showed that the volume and surface area in wheat endosperm displayed a bimodal distribution by its diameter of 10μm, while the number displayed a single peak. The results of crystalline properties showed that the crystalline structure of A, B type starch granules were typical "A" type and the crystalline value of A type starch granule is totally notable larger than that of B type, the same trends as the value of four shape peaks.The analysis of correlation relationship study between size distribution and crystalline properties showed that the crystallinity of A type starch granules have extremely positive significant associated with the volume of A type, but have negative or extremely negative significant with surface area and number distribution of B type starch granule, thus the crystallinity of B type starch granules have extremely negative significant with the volume of A type, whereas have positive significant or extremely significant with surface area and number distribution of B type starch granule in wheat.