Effect of citric acid on collagen sheets processed by compression

In this work, bovine collagen was treated with different contents of citric acid and the functional properties of the sheets prepared by compression moulding were investigated. Fourier transform infrared (FTIR) spectroscopy and mechanical properties gave indirect evidence that citric acid-incorporated collagen sheets preserved the triple-helix structure of the native collagen. Although citric acid did not react with collagen through covalent linkages, collagen structure was stabilized by hydrogen bonding between citric acid and collagen, as shown by FTIR results. These interactions enhanced mechanical properties, both tensile strength and elongation at break. Moreover, swelling capacity increased with the addition of citric acid as a result of the formation of some microvoids in the internal structure of collagen, as observed by SEM analysis.