I bought a big bag of trimethylglycine (TMG - betaine) from a reputable source and noted that it smelled faintly of rotting fish. Apparently, TMG degrades into trimethylamine (TMA), which oxides into TMAO, which is associated with bad health outcomes.
Is Betaine HCl more stable against such degradation? I'd prefer not to eat straight up TMAO when it can be avoided (yes, I know it is found in fish).