Application of quality index method for determination of shelf life of gutted greenback grey mullet (Chelon subviridis) stored at ice

The objective of this study was to evaluate the freshness of gutted greenback grey mullet Chelon subviridis stored on ice up to 18 days. Changes during storage were observed with sensory evaluation (Quality Index Methode QIM), pH, total volatile basic nitrogen (TVB-N), trimethylamine nitrogen (TMA-N), thiobarbitoric acid (TBA), free fatty acid (FFA), color and microbiological analyses (mesophilic, psychritrophic, Staphylococcus, Entrobacteriaces and H₂S- producing bacteria counts). The maximum shelf life of gutted greenback grey mullet stored in ice was determined with loss of freshness (sensorial, physico-chemical, color and microbiological evaluations). High correlation r²= 0.922 between Quality Index (QI) and storage time was verified. QI ranged from zero (maximum freshness) to 15 (total loss of freshness) and reached the acceptable limit for consumption (QI=12.66), which corresponds to a period of 12 days. QI showed a linear relationship to storage time (QIM= 8.00× storage time-9.733, R²= 0.990), and the remaining storage time could be estimated with an accuracy of ± 3 days. The microbiological results showed an increase of mesophilic, psychritrophic, Staphylococcus, Entrobacteriaces and H₂S- producing bacteria counts along the storage time. TVB-N ranged from  5.93 to 32.66 mg N/ 100g, TMA-N from 3.58 to 16.00 mg N/100g, pH from 6.87 to 7.26, TBA from 0.66 to 1.93 and FFA from 1.05 to 8.41 in the first and 16^th day of storage, respectively. It is suggested that gutted greenback grey mullet has to be fresh and acceptable for consumption by cooling up to 12 days.