Optimization of extraction conditions for residual proteins in aged silk fabrics

Abstract This study employs response surface methodology to optimize the extraction parameters of a CaCl₂/ethanol/H₂O solvent system for isolating residual proteins from simulated silk fabric samples. A Box-Behnken design was used to evaluate the effects of CaCl₂-to-H₂O molar ratio (0.005–0.045), ethanol-to-H₂O molar ratio (0.25–0.45), temperature (80–100 °C), and extraction time (120–320 min) on protein extraction efficiency. Multivariate regression analysis was applied to fit the data to a quadratic polynomial equation, validated statistically. The optimal extraction conditions were CaCl₂-to-H₂O molar ratio 0.032, ethanol-to-H₂O molar ratio 0.354, temperature 86 °C, and extraction time 248 min, achieving an efficiency of 45.733%, closely matching the theoretical prediction (46.523%). The effects of extraction on protein structure were assessed using sodium dodecyl sulfate - polyacrylamide gel electrophoresis, ultraviolet-visible spectroscopy, and circular dichroism spectroscopy, revealing that optimized conditions improved efficiency while better preserving molecular weight and secondary structure.