IMPACT OF TEMPERATURE ON THE STABILITY OF SILKWORM COCOON FIBERS

In this study raw and processed silkworm (Bombyx mori) cocoons were investigated using confocal Raman spectroscopy in conjunction with differential scanning calorimetry (DSC) in order to examine the effect of temperature on the molecular conformation of silk fiber structures. Using DSC, a broad endothermic curve was observed at moderate temperatures, shedding light on the vaporization of both raw and processed cocoons, a phenomenon that could also indicate a strong interaction between silk fibroin and water molecules. Over the temperature range set for this study, Raman spectra of raw and processed cocoons were compared at different excitation radiations after drying both kinds of cocoon in an oven at 80 and 125 ºC for 60 minutes. By correlating the intensity ratios of the deconvoluted Raman bands using the broad bands characteristic of amide I and III, it was possible to evaluate the conformational changes in both materials. At excitation radiation of 532 nm, the deconvoluted Raman spectra for the amide III band indicated that, for both samples, there was a reduction in β-sheet conformation compared to α-helix conformation, and this structural disruption was driven by increased temperature. At radiation of 785 nm, the bands attributed to amino acid residues in the side chains increased in intensity, and by deconvoluting the amide I band, increased temperature was found to induce a transition from β-sheets to β-turns in both materials.