The amino acid compositions of the different samples revealed that
they are rich in Gly, Pro and Leu. It is known that Gly, Hyp and Pro are
abundantly present in connective tissues containing collagens [44],
thus the high content of glycine and proline present in the undigested
thornback raymuscle indicated that a highamount of connective tissues
was present in the raw material. The sum of Gly, Hyp and Pro was between
22.04% for TRMH-Alcalase and 26.82% for the undigested protein.
This amount was higher than that of salmon (20.37%) and cod (7.15%)
protein hydrolysates