[Interaction of fish collagen peptide with epigallocatechin gallate]

Fish collagen is known to have good moisturising property and antioxidant ability, which has been increasingly added into cosmetics, foods and drinks as thicker agent and to increase dietary supply of collagen. Fish collagen peptide (FCP) is a white or pale yellow powder, obtained by extracting collagen from sources including the scales and bones of fish such as bonito, halibut, tuna, and sea bream. It is identical to human collagen and 100% absorbable through the skin. (-)-Epigallocatechin-3-gallate (EGCG), the major constituent of green tea, has lots of beneficial biological and pharmacological effects, including antioxidant, antimutagenic, antiviral and antiinflammatory activities. Because proteins have the desirable formulation of EGCG-fortified food, the interaction between proteins and EGCG molecules has been widely studied. At the same time, the interaction of proteins and EGCG was known to affect the content of free EGCG, structure of proteins, antioxidant capacity of EGCG in foods. But, to our knowledge, the interaction between FCP and EGCG has not been characterised clearly, and little is known about their interaction mechanism. Therefore, a better understanding of the interaction between FCP and EGCG would help to control their functional properties in food products during processing, transportation and storage when we facilitate FCP as the vehicles for EGCG. In view of the above, we planned to study the interaction of FCP with EGCG by using different spectroscopic techniques, such as fluorescence spectroscopic, FTIR, CD and Raman. EGCG caused a concentration dependent quenching of the intrinsic fluorescence of tyrosine residue in the FCP, indicating the occurrence of interactions between FCP and EGCG. Excimer-like species and dityrosine were regularly formed with the addition of EGCG into the solution, and the interaction of FCP and EGCG partly disrupted the structure-of the protein. Synchronous fluorescence results indicate that the interaction caused decrease of the polarity around tyrosine residues resulting in FCP conformation alteration. FTIR showed that the frequency of 3 281 and 1 248 cm-1 declined, the absorption peaks at 3 076 and 1 547 cm-1 had a slight red-shift, the absorption peaks at 1 659 and 1 689 cm-1 had a slight blue-shift in the FCP-EGCG complexes. It is interesting to observe that the CD intensity of FCP around 198 nm decreased with high EGCG concentration, and the peak maximum shifted to a larger wavelength (red shift). Raman spectra showed that peaks at 863 and 932 cm-1 had a slight red-shift, and decreased intensities near 932 cm-1 suggested that more exposure of proline when FCP-EGCG complexes formed. This study provides a theoretical basis for fortifying FCP products with EGCG.