Abstract: The nutrient compositions of the muscle and hepatopancreas of hard- and soft-shell crabs (Scylla paramamosain) were comparatively analyzed by nuclear magnetic resonance (NMR) based metabolomics. The results showed that when compared to hard-shell crabs, soft-shell crabs at 0 h postmolt had significantly lower levels of lysine, arginine, lactate and trimethylamine-N-oxide (TMAO) in muscle. The decreased levels of lysine, arginine and lactate may have little impact on the nutritive value and taste of crab muscle, whereas the decreased level of TMAO may reduce the risk of illness in consumers. Furthermore, the significant fluctuations of four amino acids and betaine in the hepatopancreas of soft-shell crabs at 0 h postmolt likely affected the taste of hepatopancreas. The muscle and hepatopancreas of soft-shell crabs at 3 h postmolt showed more significant changes in nutrient composition. Especially, there was a significant decline in 5’-adenosine monophosphate (AMP) in muscle, presumably affecting the umami taste. Moreover, the levels of histidine, tyrosine and glucose in hepatopancreas were significantly decreased from 3 h postmolt, likely reducing the nutritional value of this tissue. Therefore, newly molted soft-shell crabs might have nutritional value similar to that of hard-shell crabs in terms of the composition of low molecular mass nutrients, being a healthier aquatic product. However, delayed harvest may affect the quality and taste of soft-shell mud crabs.

Key words: Scylla paramamosain, soft-shell crab, nutrients, nuclear magnetic resonance (NMR), metabolomics