The fluorescence spectra were recorded using a spectrofluorimeter FluroMax-2 (Spex-Jobin Yves, Longjumeau, France). The emission spectra were collected in the range of 305–400 nm, 340–540 nm and 410–700 nm after fixing the excitation wavelength at 290, 322 and 382 nm, respectively. No sample preparation was used in this study for the collection of spectra. The spectra of muscle samples (2 cm × 1 cm × 0.5 cm), mounted between two quartz slides were recorded directly on the surface of the meat sample. The measurements were repeated twice on different test specimens for each muscle sample.