Thanks Al, I would have thought that with the mussels being precooked and my blanching I would have exceeded that requirement. My observations are purely empirical but nonetheless the difference between when I was feeding mussels and after I stopped was quite obvious. Some thiaminase isoenzymes are more heat resistant than others, the extreme being that found in Anaphe venata (wild African silkworm) that requires 15 minutes at 100C.
I personally have come to the conclusion that mussels meat is to much trouble to be used safely as a main ingredient.