FT-IR and Raman spectroscopies determine structural changes of tilapia fish protein isolate and surimi under different comminution conditions

•The FT-IR spectra showed fewer bands in FPI samples than surimi samples.•The degree of unfolding in protein structure of FPI and surimi paste changed by comminution conditions.•FPI and surimi gels chopped at 25°C for 18min showed higher chemical bonds than those at 5°C for 6min. Tilapia proteins refined by pH shift and water washing were chopped under various comminution conditions and their structural changes were investigated using Fourier transform infrared (FT-IR) and Raman spectroscopies. Both techniques revealed the degree of unfolding in protein structure increased when fish protein isolate (FPI) and surimi were chopped at 25°C for 18min compared to samples chopped at 5°C for 6min. Results indicated both hydrophobic interactions and disulfide bonds were significantly enhanced during gelation. FPI and surimi gels prepared at 25°C for 18min exhibited higher β-sheet contents and more chemical bonds such as hydrophobic interactions and disulfide bonds than those at 5°C for 6min. Results suggested that controlling comminution is important to improve gel qualities in FPI and surimi from tropical fish like tilapia. Moreover, FT-IR and Raman spectroscopies are useful complementary tools for elucidating the change in the structure of protein during comminution and gelation.