LIPID AND PROTEIN THERMOTROPIC TRANSITION OF PORCINE STRATUM-CORNEUM BY MICROSCOPIC CALORIMETRY AND INFRARED-SPECTROSCOPY

Microscopic differential scanning calorimetry and Fourier transform infrared spectrometry (DSC-FTIR) were combined to investigate the thermal response and IR spectra of lipid and protein in the process of a phase transition in porcine stratum corneum (SC) by KBr disc method. The alterations of bands associated with the CH, stretching vibrations near 2850 and 2920 cm-1 were used to determine the phase transformation of lipid with temperature. The peaks of amide I and II of protein were used to investigate the thermal conversion of protein. A reheating process was performed. The results indicate that the bands of lipid near 2900 cm-1 shifted to greater wavenumber with increased temperature, but reversibly. The band due to deformation mode of the lipid altered from shoulder to smooth with increased temperature. During heating, alpha-keratin of the protein transformed gradually to beta-keratin, but irreversibly. Thermal transitions that occurred near 78-degrees-C and 115-degrees-C for the sample on first heating were associated with phase transition of the lipid-protein complex and the protein in porcine SC, respectively. After reheating, this phase transitional temperature of the lipid-protein complex in porcine SC decreased froin 78 to 68-degrees-C, and the transition of protein near 115-degrees-C almost disappeared. This behaviour indicates that porcine SC after heating might alter its structure. The thermally altered proportion of lipid was 43.98% and the thermally induced proportion of protein was 41.48% during the first beating process, but the restoration of lipid during the cycle of heating, cooling and reheating was 37.64%. The variation is attributed to the denaturation of protein to alter the structure of lipid-protein complex after first heating. This technique was simple, precise and reproducible for simple determination of stratum corneum or biological samples in a brief period.