Evaluation of the effects of vacuum packaging on the shelf life of ready-tocook (RTC) marine fish sausages at frozen storage conditions

Vacuum packaging combined with low storage temperatures is an effective technique for extending the shelf life of fishery products. Ready-to-cook (RTC) fish sausages from marine fish (tuna, mackerel, and croaker) were produced by optimizing ingredients and processing conditions. Shelf life was assessed by analysing moisture, pH, free fatty acid (FFA), thiobarbituric acid reactive substances (TBARS), and aerobic plate count (APC) at monthly intervals during frozen storage under packaging in a multilayer plastic pouch. The protein content of fish sausages was 10.92-13.44%, with the highest protein found in tuna sausage and the lowest in mackerel sausage. Croaker sausage was the lightest in comparison to the tuna and the mackerel sausages. The hardness value of mackerel sausage was higher than that of tuna and croaker sausages. The moisture content ranged from 57.23-58.99%, where with the highest value found in a croaker sausage and the lowest in a tuna sausage. Significantly (p<0.05) lower moisture content was observed in the vacuum pack sample, particularly in the mackerel, compared to the control sample during the storage period. During the frozen storage period, almost all samples showed a decreasing trend in pH and an increasing trend in moisture, FFA, TBARS, and APC levels. No significant differences (p>0.05) were observed in FFA values between the air-packed and vacuum-packed samples during the frozen storage period. However, moisture, pH, FFA, and TBARS values were within the acceptable limits during the frozen storage period. The APC exceeded the acceptable limit (7 log CFU/g), at approximately 6 months for air-packed and 7 months for vacuum-packed tuna sausage; 5 months for air-packed and 7 months for vacuum-packed mackerel sausage, and 4 months for air-packed and 6 months for vacuum-packed croaker sausage. Vacuum packaging showed slightly better results compared to air packaging in extending shelf life, which could be utilised by small-scale entrepreneurs for fish sausage production.