Elemental and structural changes associated with white spot formation in sun-dried Pacific white shrimp shells

Structural and elemental properties of dried Pacific white shrimp (WSS) (Litopenaeus vannamei) shell having the white spots were compared with non-white spot shrimp (NWSS) shell. Based on X-ray diffraction (XRD) analysis, both samples showed two characteristic peaks representing chitin. However, WSS sample had two additional major peaks at 2θ of 26.65 and 29.53º, which were related to quartz and calcite, respectively. Scanning electron microscope coupled with energy-dispersive X-ray spectrophotometer (SEM-EDX) mapping showed the movement of various elements towards the exo- and endocuticle. The Raman spectroscopic study confirmed the formation of calcite crystals in the white spots. The looser chitin matrix was obtained for WSS as compared to that of NWSS as depicted in SEM micrographs. Therefore, the white spots developed in the shell were caused by the formation of calcite, which exhibited different structural arrangements and elemental positioning as compared to shrimp shell without white spots.