Study On The Relationship Between Structural Changes And Surface-activity Of Silk Protein

Silk fibroin composed of hydrophobic and hydrophilic amino acids linked together by peptide bonds, should have good surface-activity. However, due to specific structure of silk fibroin or coiling fold of polypeptide chains, the presence of crystalline region and the amorphous region and spatial structure forces such as disulfide bonds, hydrogen bonds, most of silk fibroin couldn’t demonstrate their surface-activity as the hydrophobic groups of silk fibroin wrapped inside the compact and stable protein molecules. Therefore, in order to explore the relationship between the structure and surface active properties of silk fibroin, great deals of research works have been done in this thesis.1. This paper focused on the influence of w(Ca Cl2), liquid-solid ratio, dissolving time and dialysis time on yield of silk fibroin, content of soluble protein, emulsion capacity, foaming capacity, emulsion stability and foaming stability. Then the structural periodic variation characteristics of silk fibroin dissolved in Ca Cl2 were studied by spectroscopic techniques(e. g. static fluorescence spectroscopy, UV-vis absorption spectroscopy and Raman spectroscopy).The results showed that the optimum preparation conditions for soluble silk fibroin were determined as w(Ca Cl2) of 38%, liquid-solid ratio of 1:12, dissolution time of 15 min and dialysis time of 20 h. Yield of silk fibroin, content of soluble protein, emulsion capacity, emulsion stability, foaming capacity and foaming stability could separately reach 47.82%, 46.53 mg/m L, 95.16%, 92.47%, 221.56% and 88.29%. In addition, molecular conformation mainly shifted from β-sheet to α-helix or random coil, and Trp and Tyr buried in the area of noncrystalline also were gradually exposed with the extension of dissolution time from 0 min to 30 min. At the same time, the circumstances of chromophoric groups changed from nonpolarity to polarity. Therefore, the surface-activity of water-soluble silk fibroin increased gradually.2. The structural characteristics, solubility and surface-activity changes of silk fibroin at assistance of microwave were analyzed. And the structural changes of silk fibroin before and after microwave assisted were characterized by Fourier transform infrared and scanning electron microscopy.The results indicated that the best conditions of preparation soluble silk fibroin by microwave-assisted were w(Ca Cl2) of 38%, solid-liquid ratio of 1:11, assisted dissolution time of 3 min, dialysis time of 25 h and microwave power of 236 W, in which yield of silk fibroin, content of soluble protein, emulsion capacity, emulsion stability, foaming capacity and foam stability could separately reach 62.37%, 47.28 mg/m L, 95.83%, 93.57%, 232.50% and 92.78%. Moreover, silk fibroin solution prepared by microwave assisted formed more intermolecular hydrogen bonds, enhancing the solubility of silk fibroin, thereby improving the performance of water-soluble silk fibroin.3. The structural characteristics, solubility and surface-activity changes of silk fibroin in the presence of ethanol were analyzed. The results indicated that adding ethanol coule improve solubility. Meanwhile, with the addition of ethanol, the hydrophobic region of the silk fibroin gradually destroyed, so that hydrophobic groups were gradually exposed in solution. As a result, it reached much lower surface tension and critical micelle concentration, and improving the emulsion capacity, emulsion stability, foaming ability, foaming stability and decontamination.