Effects of Different Salt Concentrations on Several Freshness Indicators of North Pacific Squid (Ommastrephes sloani pacificus) during Storage at 4°C

The effects of salt treatment (2% [w/w] low salt and 6% [w/w] high salt) and storage time (0 to 12 days) on two biogenic amines (histamine and tyramine), total volatile base nitrogen (TVB-N), pH, and volatile compounds of the North Pacific squid during storage at 4°C were evaluated. The freshness of squid muscle was evaluated by monitoring the changes in these indicators during storage. Results showed that histamine and tyramine contents increased with storage time (4.29 to 22.47 mg/kg for histamine and 28.10 to 135.78 mg/kg for tyramine) and that, in samples treated with salt, formation of these amines can be effectively inhibited (P < 0.05) compared with untreated samples. The overall pH level initially decreased and then increased during storage (ranging from 6.49 to 7.13), and the pH level of the two salt treatment groups was a little lower than that of the control group. The TVB-N value increased with time and was effectively inhibited by salt (P < 0.05). The number and content of the volatile components in squid varied during the entire storage time. The main volatile components detected in North Pacific squid were aliphatic hydrocarbons, alcohols, aldehydes, ketones, acids, esters, aromatic hydrocarbons, phenols, nitrogenous compounds, sulfo compounds, and esters. Several compounds, such as trimethylamine, butyric acid, and sulfureted hydrogen, can be used to determine the quality of aquatic products, and salt treatment can inhibit their formation. The TVB-N value was significantly correlated with pH level and with the concentrations of histamine, tyramine, and several volatile compounds in all samples (P < 0.05). In summary, salt concentration had a positive effect on extending the shelf life of North Pacific squid, and multiple indicators should be used to determine the quality of squid.