Yellowing Mechanism Of Skin Collagen And Its Affecting Factors

Type I collagen, maintained a stable three-helical structure, was extracted through the acid solution-enzymatic method from raw rabbit-skin. The extracted collagen was experienced artificial UV yellowing and heat yellowing, respectively. The results showed that,ΔE*a,b of skin collagen films increased with the processing time of the heat treatment as well as UV treatment. After 24h treatment,ΔE*a,b with UV treatment was higher than that with heat treatment(80℃). Besides, there existed the logarithm of the correlation betweenΔE*a,b and the treatment time with coefficient was higher than 0.990. The results of the Infrared spectrum showed that skin collagen underwent a chemical reaction under UV and the heat, but their roles were different. The structure in the collagen molecular changed, and the helical structure turned to random coil transition. The UV spectra results showed that in the early exposure of the ultraviolet, there were new unsaturated conjugate groups formed. With the exposure time increased, a decreased absorbance was observed. SEM pictures showed after irradiation and heat treatment, the collagen structure was destroyed.In this paper, cross-linked collagen films with different amount of glutaraldehyde were prepared and characterized. When the amount of glutaraldehyde was 0.75% of collagen, the effect of cross-linking was the best. IR spectra indicated that collagen structure was more stable after the modification by glutaraldehyde. However, adding glutaraldehyde increased the yellowing degree of collagen, which can be attributed to its self-polymerization with glutaraldehyde.The impact of tanning agents on yellowing of the skin collagen was also studied. It was found that the yellowing resistance of aluminum sulfate tanned skin collagen was better than the synthetic tannin tanned skin collagen. Infrared analysis also confirmed that. Thermal analysis showed that after tanning the UV resistance of the skin collagen was improved, and thermal degradation activation energy presented the trend of first increases and then decreased after yellowing. The hydrothermal shrinkage temperatures (Ts) of the samples were significantly decreased after yellowing. Ts of the skin tanned by aluminum sulfate was decreased the most. The hydrothermal stability of aluminum sulfate tanned sample was poorer than that of tannin tanned.