Nucleotides and derived compounds of undigested muscle and
TRMHs were determined by HPLC and shown in Table 2. IMP is the
major compound in the undigested muscle (31.02 μmol/g). IMP was
also reported to be the major nucleotide compound in white muscle
of milkfish (Chanos chanos) [36]. Hypoxanthine is the major compound
in all the hydrolysates (from25.84 to 58.68 μmol/g), while ATP and uric
acid were undetectable. AMP was not detected in TRMH-A26, TRMHAlcalase
and TRMH-Crude; IMP and inosine were also not detected in
TRMH-Crude. After death, ATP is rapidly split into ADP and subsequently
into AMP and IMP. IMP is then degraded to inosine and hypoxanthine
which in turn can be oxidized to uric acid [37]. So, the accumulation of
hypoxanthine in the fish muscle hydrolysate can reflect the occurring
of enzymatic breakdown. Nucleotides and especially IMP and GMP,
which are abundant in seafood, are responsible for theumami taste sensation
[38]. The presence of these nucleotides in TRMHs and especially
in the undigested muscle, contributes to the umami sensor. However,
it has been noted that the combination of nucleotides with umami
amino acids (aspartic and glutamic acids)would increase synergistically
the umami response.Many researcheswere focused on the umami taste
of seafood to reduce the need for added salt, as well as providing components
possessing bioactivities such as antioxidant activity from
brown seaweeds [39] or ACE inhibitory activity fromshrimp processing
by-product hydrolysates