Streaks in Salmon
A complaint was made regarding a shipment of salmon fillets. Upon receipt at their destination, the salmon fillets were found to have white spots distributed over their surfaces. Microtrace was asked to analyze this material and determine its source.
When examined by stereomicroscopy the white spots were observed to be discrete crystalline clusters located beneath the surface of the fish tissue. Samples of the white material were excised and cleaned of fish oil and tissue. One relatively common crystal formation in seafood is struvite, a precipitate of magnesium ammonium phosphate; however, these crystals were not optically consistent with struvite and elemental analysis indicated they were entirely organic in composition. Further examination by light microscopy revealed that this material recrystallized into monoclinic prisms in water. Infrared spectrophotometric analysis of this recrystallized material identified the material as creatine.
Creatine is utilized in the production of energy and can be biosynthesized at low concentrations. Additionally, creatine is a common dietary supplement which is consumed to aid in muscle growth. The presence of precipitated creatine may suggest that it was used at a level higher than could be absorbed by the tissue of the fish, resulting in precipitation of the less aesthetically pleasing creatine crystals.