Analysis of the Effects of pH and Salt on the Conformation of the Sericin Particles by DLS and TEM Measurements
WU Li-ping1, LENG Xiao-jing1, SUN Yan1, REN Fa-zheng1*，Nakai Shuryo2
1. CAU&ACC Joint-Laboratory of Space Food, Key Laboratory of Functional Dairy Science of Beijing and Ministry of Education, College of Food Science & Nutritional Engineering, China Agricultural University, Beijing 100083, China 2. Department of Food, Nutrition &Health，University of British Columbia, Vancouver, V6T 1Z4, Canada
Abstract：The particles conformation of the sericin protein extracted from silkworm Bombyx mori was studied under the conditions of different pH and salt concentrations by infrared spectroscopy (IR), dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements. The IR spectrum of sericin protein arises predominantly from CO stretching vibration around the amide I region of 1 700-1 600 cm-1. A strong trend of aggregation of the protein could be observed under specified experimental conditions. The apparent isoelectric point of the sericin protein was about 3.7. The DLS method was used to investigate the effects of pH and NaCl on the size distribution, where a large polydispersity of the system could be observed. Compared to pH 4 or high NaCl concentration, at pH 3, 8 or low NaCl concentration the sericin aggregation shows a relatively smaller size but larger polydispersity. TEM was used to investigate the microstructure of the aggregated sericin protein, where a loose and pine-like branched form could be observed at pH 3 or 8; however, a relatively compact structure was observed near pH 4 or at high salt concentration. At pH 4 the spherical monomer size can be calculated at around (60±6) nm (n=10) by TEM measurement. These phenomena could be explained by the effects of the electrostatic repulsion, hydrogen bonding and Van der Waals attractive force, which provide a basic theory for the application of sericin as biomaterial.
Key words：Sericin;Aggregation;Microstructure;DLS;TEM;IR;Hydrogen bonding;Van der Waals force
吴丽萍1，冷小京1，孙 雁1，任发政1*，Nakai Shuryo2 . 动态光散射和透射电镜法研究pH和NaCl对 丝胶蛋白微观结构的影响[J]. 光谱学与光谱分析, 2010, 30(05): 1391-1395.
WU Li-ping1, LENG Xiao-jing1, SUN Yan1, REN Fa-zheng1*，Nakai Shuryo2 . Analysis of the Effects of pH and Salt on the Conformation of the Sericin Particles by DLS and TEM Measurements . SPECTROSCOPY AND SPECTRAL ANALYSIS, 2010, 30(05): 1391-1395.
