Extraction of insoluble fibrous collagen for characterization and crosslinking with phenolic compounds from pomegranate byproducts for leather tanning applications

An environmental approach for leather manufacturing is primordial to provide a global strategy towards more sustainable biomaterials and greener tanning processing methods. The ability of collagen as a principal component of skin to combine natural phenolic compounds, especially vegetable tannins, has been proven to be eco-friendly and manageable, while making good improvement to leather properties in the tanning process. In this study, we have used pomegranate phenolic compounds and insoluble collagen as a model system to examine the effects of tanning steps on the conformation of collagen. In detail, efficient modified extraction of pure insoluble collagen (IC) was presented. The IC was successfully identified using XRD, FTIR, SEM-EDS and TGA-DSC to verify the triple helix structure, morphology and thermal properties. As a result, the as-extracted collagen exhibits a high purity, preserving the triple helix collagen structure. Besides, the IC was modified using extracted pomegranate phenolic compounds, resulting in Crosslinked Insoluble Collagen (CIC). Characterization techniques were also performed to confirm the crosslinking process. Indeed, by comparing the FTIR vibrational spectra of IC and CIC, slight shifts of amide groups were observed, indicating the presence of inter and intramolecular interaction between IC functional groups and pomegranate phenolic compounds. Moreover, the morphology of CIC was changed. XRD analysis confirms collagen conformational integrity. Finally, thermal properties were improved. The temperature at 50% weight loss (T°(50)) increases from 344.54 °C to 375.53 °C. CIC multifunctionality allowed utilizing pomegranate phenolic compound extracts as a tanning agent in leather processing.