Comparative study on chemical composition, thermal properties and microstructure between the muscle of hard shell and soft shell mud crabs

Chemical composition, thermal properties and microstructure of the muscle from hard shell and soft shell mud crabs were studied. Both lump and claw muscle of soft shell mud crabs contained a lower protein content but higher moisture and salt contents than those from hard shell mud crab (p < 0.05). Calcium and magnesium were the major minerals in the muscle of hard and soft shell mud crabs (240.5–699.2 ppm). Approximately one-third of calcium was observed in the muscle of soft shell mud crab, compared to that of hard shell mud crab. Copper, iron and zinc were the trace minerals with the amount less than 50 ppm. Hydroxyproline content ranged from 7.92 to 8.88 mg/g wet muscle in all samples, except claw muscle from soft shell mud crab, which contained considerably low hydroxyproline content (2.75 mg/g wet muscle). Sarcoplasmic and alkali-soluble proteins were the major constituents in all muscles, except claw muscle from soft shell mud crab, in which sarcoplasmic protein was the dominant component. Tmax from myosin of lump muscle were 47.58–48.08 °C with enthalpy of 0.20–0.21 J/g, whereas myosin from claw muscle had lower Tmax (45.00–47.48 °C) with lower enthalpy (0.17–0.18 J/g). Lump muscle bundles of hard and soft shell mud crabs aligned orderly, while claw muscles of both crabs had partial disintegrations and the porous structure was observed in that from soft shell crab.