Dietary Calcium from Pearl Oyster (Pinctada maxima) Shell Powder as Affected by Thermal Treatment : Characterization and Its Application in Surimi Gel

Chemical composition of pearl oyster ( Pinctada maxima ) shell as affected by thermal treatment at 900 °C for 5 hours was investigated. The shell powder (SP) without thermal treatment and its calcine powder (CP) were characterized. Both samples contained the high ash content of 95.74-99.37%, which found as a major component. Calcium contents were presented at 41.17-62.04%, while protein moisture and lipid content were found 3.12%, 0.38-0.68% and 0.10%, respectively. Moreover, thermal treatment also affected the color as evidenced by higher whiteness and L* (Lightness) values with concomitant decreases in a* (Redness) and b* (Yellowness) values of CP. When SP and CP at various levels (0.025-0.5%) were incorporated in mixed fish surimi, their gelling properties were investigated, which comparatively studied with the gel containing calcium chloride (CaCl 2 ). With the addition of calcium level (0.025-0.075%), the increases in breaking force and gel strength of all gels were observed (P 0.05). In addition, the increase in gel forming ability was associated with the decreased expressible moisture contents as well as the increased in whiteness. The addition of calcium powders from pearl oyster shell at 0.075% was an appropriate level for gel improvement from mixed fish surimi. The higher gel forming ability induced by SP was found than did CP, similarly to gel added with CaCl 2 . The result indicated that calcium compound, an endogenous transglutaminess (TGase) activator, plays an important role for gel improvement. Thus, pearl oyster shell powder could be an alternative source of natural calcium for gel enhancement and color improvement for low graded surimi from mixed fish. Keywords : calcium ; pearl oyster shell powder ; chemical composition ; gelling properties ; surimi