Reduction of formaldehyde residues induced by the thermal decomposition of trimethylamine oxide during the processing and storage of jumbo squid (Dosidicus gigas)

Thermal decomposition of trimethylamine oxide (TMAO) during the processing and storage of jumbo squid was characterized to find an innovative approach to its safe consumption. A combination of Fe2+ with ascorbic acid (AA) promoted the almost complete degradation of TMAO from 438.89 mg/L to 0.23 mg/L, generating considerable equimolar amounts of dimethylamine (DMA) and formaldehyde (FA). Moreover, the role of “Fe2+ + AA” on the decomposition of TMAO could be significantly altered by varying the pH values. At pH 9, TMAO was degraded through two different pathways to give trimethylamine (TMA) with content of 148 mg/L and DMA of 57 mg/L, while at pH 3, TMAO was mainly transformed into TMA (210 mg/L) but a small amount of DMA (15 mg/L). Water activity (aw) and water mobility were also found to influence the formation of FA, as it obviously dropped from 136.6 μg/g to 100.6 μg/g when aw was reduced from 0.750 to 0.667 with less free water. Interestingly, during accelerated storage experiment, the quantity of FA increased prior to decreasing. This was attributed to its role in crosslinking the squid muscle fibers to give a stable network structure and significantly altering the microstructures observed by scanning electron microscopy.