Endogenous Trypsin Triggers Free Fluoride Release from Antarctic Krill (Euphausia superba) Cuticle

During postmortem storage, fluoride in Antarctic krill can be enriched in the muscle. Trypsin, as the most important digestive enzyme in Antarctic krill with a high activity in low temperature, plays a potential role in this process. In this study, endogenous trypsin was purified and its properties were investigated. The involvement of trypsin in the generation of free fluoride from Antarctic krill cuticle was explored. Cuticle microstructure before and after hydrolysis was compared with scanning electron microscopy, and the ash samples of the hydrolyzed Antarctic krill cuticle were analyzed with X-ray diffraction, Fourier transform infrared spectroscopy, and electron dispersive spectroscopy, respectively. Mass spectrometry analysis and inhibition tests confirmed that the purified enzyme was endogenous trypsin. Results of the present study indicated that trypsin digestion caused the increases of the concentrations of both fluoride ions and free amino N simultaneously, while the protein coated on the cuticle surface was dissolved too. However, no compositional change was detected in the cuticle inorganic salts. These findings suggest that trypsin triggered free fluoride release from Antarctic krill cuticle. In addition, the kinetics of free fluoride release could be described by the equation CW = (1−0.97−0006t −0.03e0.0558t)×337.53+10.50. The present study improved the understanding of the role of trypsin in free fluoride release from Antarctic krill cuticle, facilitating future studies aimed at reducing the fluoride content in krill protein during Antarctic krill processing.