Preparation And Application Of Soluble Silk Fibroin

Silk protein, a bioactive protein, has been considered as a new protein source. It has been used as functional ingredient in both foods and medicine. The objective of this thesis is mainly to study preparation and application of soluble silk fibroin (SF) from waste silk.A suitable process for the preparation of soluble SF powder was developed. Based on the understanding that desalting was the most difficult step to get soluble SF powder, several desalting methods were investigated. The results indicated that ultrafiltration with organic and inorganic ceramic membrane was somewhat effective in desalting, but NSI of the resulted product was low because of the denaturation of protein during ultrafiltration. Dialysis was effective in desalting and the resulted product had a high NSI of 99.8%, but the treating time was intolerable long because of the low desalting efficiency of dialysis the solution with low salt concentration. Dialysis-ion exchange desalting process was developed. The solution was desalted by dialysis at SF concentration of crude material 9%(w/v) and a flow rate of 40L/hr. The transition from dialysis to ion exchange resin was conducted when the electrical conductivity of solution reduced to 14000μs/cm. After spray drying, a product with a protein content of 95.25%,NSI of 98.6%,ash content of 0.78%,moisture content of 3.77% was obtained. .Amino acid analysis showed that glycine, alanine, serine and tyrosine residues were the main amino acid residues of SF, and the total amount of these four animo acid residues was near 84%. Sephacryl S-200 gel filtration chromatography revealed that the average molecular weight of the components of SF was 70,000Da.Functional properties of SF were measured. SF could decrease surface tension because of its surface activity. Surface hydrophobicity of SF was increased significantly after high-speed shearing. In the pH range of 3 to 10, Emulsion Capacity (EC) and Emulsion Stability (ES) of SF were good, and they all improved greatly with the increase of concentration of SF. NaCl had slight effect on the EC and ES of SF. Foaming Capacity (FC) and Foaming Stability (FS) of silk fibroin were also improved with the increase of concentration of silk fibroin and NaCl. SF had the highest FC and FS at pH 5. Gelation of SF solution became more quickly and the formed gels became stronger with the increase of the concentration of SF. Gelation had the highest speed at pH3~4. Surface tension decreased significantly with the increase of the concentration of SF, but increased with the increase of concentration of NaCl. SF was applied in the production of noodle and cake. With the addition of SF, the texture of noodles degenerated slightly. Noodle fortified with SF had a lower hardness, breaking force, and chewness than the control. The texture of the noodle fortified with SF was improved with the addition of guar gum. The volume-weight ratio and springiness decreased with the increase of concentration of SF. SF was helpful in keeping moisture and could prevent cake from staling. The quality of the cake was not acceptable at higher concentration than 0.5%(w/w).