The Application Of Raman Spectroscopy In Structure Analysis Of Starch

In this paper, acid hydrolyzed starch, B-type microcrystalline starch, amorphous starch and V-type starch were prepared from natural corn starch. X-ray diffraction(XRD) and Raman spectroscopy were used to analyze the structure of these four types of starches. It has built the foundation for the application of Raman spectrometer on the research of starch structure.(1) The application of Raman spectroscopy in structure analysis of corn starch. We prepared acid hydrolyzed starch, B-type microcrystalline starch and amorphous starch from natural corn starch. The X-ray diffraction and Raman spectroscopy were used to analysis the structure of above five types of starch. The results show that natural corn starch and acid hydrolyzed starch are A-type, microcrystalline is B-type. The height of baseline in Raman spectra of the four samples means the content of fluorescent composition. The results show that the height of baseline in Raman spectra of natural corn starch is the highest and which of B-type is the lowest. The Raman spectra of amorphous starch did not have intense Raman peak. The intensity of each Raman peak is related to the size of the crystalline region. Because that natural corn starch and acid hydrolyzed starch are A-type, the position and intensity of Raman peak is basically consistent.However, in the Raman spectrum of B-type starch, part of the scattering peak vibration wave reduces because of the changes of crystal type.(2) The application of Raman spectroscopy incrystallinity calculation of corn starch. By taking the scattering peak area in Raman spectrum as the crystalline region and the total area under the scattering curve minus the fluorescent area as the sum of the amorphous and crystalline regions, we have established a method for calculating the crystallinity of starch samples by Raman spectra. The crystallinity of starch samples was as follows(the former was the crystallinity of XRD, and the latter was the crystallinity of Raman spectra): natural corn starch was 29.8% and 24.6%, acid hydrolyzed starch was 48.5% and 50.8%, B-type microcrystalline starch was 78.2% and 82.3%, amorphous starch was 4.4% and 6.9%. The comparison of results by this calculation method with those by X-ray diffraction(XRD) indicates that when the crystallinity of sample is low, the error of this method is slightly larger. When the sample has high crystallinity, the difference of the two is small.Therefore Raman spectroscopy can be used to set up a methodfor evaluation of relative crystallinity of starches.(3) The preparation of V-type amylose-lipid compounds and analyses of Raman spectroscopy. The ligands of V-type amylose-lipid compounds in this research were glycerin monostearate(GMS), stearic acid(SA) and sodium stearoyl lactate(SSL). The best compound conditionsof three different ligands compounds were as follows:The preparation of V-type amylose-GMS complexes: The mixture was stirred under the condition of 90℃ for 2h and then heated to 100℃ for 30 min and let it stand at 90℃ for 2h and cooled at room temperature for 2 days. The weight of ligand was 0.7g.The preparation of V-type amylose-SA complexes: The mixture was stirred under the condition of 90℃ for 30 min and then 60℃, let it stand at 60℃ for 90 min. The weight of ligand was 0.06 g.The preparation of V-type amylose-SSL complexes: The mixture was stirred under the condition of 90℃ for 2h and then heated to 100℃ for 30 min and let it stand at 90℃ for 2h and cooled at room temperature for 2 days. The weight of ligand was 0.75 g.From the XRD and Raman spectra of the three kinds of V-type amylose-lipid compounds, we can see that the crystallinity of V-type amylose-GMS complexes is the highest(74.4%) and the crystalline structure of it is the best.(4) The crystallization temperature of V-type amylose-GMS complexes. We prepared V-type amylose-GMS complexes through two ways. The best compound conditionsof the ways were as follows:Constant temperature: The mixture was stirred under the condition of 90℃ for 2h and then heated to 100℃ for 30 min and let it stand at 60℃ for 8h and cooled at room temperature for 2 days. The weight of ligand was 0.7g.Gradient cooling: The mixture was stirred under the condition of 90℃ for 2h and then heated to 100℃ for 30 min, then took the gradient cooling as 20℃/h and cooled at room temperature for 2 days. The weight of ligand was 0.7g.The result of XRD and IR showed that we can get the V-type starch by above methods, and the crystallinity was all above 60%, so the methods were feasible.