Title: Shelf life trials of fresh cod and haddock stored whole on ice, using microbiological, chemical and sensory methods

Chemical and microbiological methods were evaluated during a storage trial of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) stored aerobically on ice at around 0° C. Also, sensory methods were used to determine the shelf life of these two temperate marine species. The main emphasis was on the comparison of methods used for total viable bacterial counts (TVC), isolation and identification of the spoilage micro flora that had developed during aerobic storage and understanding the behaviour of these micro organisms.

Sensory evaluation using the Quality Index Method (QIM) on whole fish and the modified Torry scale on cooked fillets were used to determine the shelf life of these two fish species. These two methods have revealed that the shelf lives of the fish stored on ice around 0°C were in the range of 11 to 14 days for haddock and cod, respectively. The chemical indices, TMA and TVB-N, were not found to be proper indicators of shelf life as low production or formation occurred during sensory storage life under iced conditions. The TMA content for cod was 6.15 mg N/100 g and 1.24 mg N/100 g for haddock. Similarly, the TVB-N content for cod (26.7 mg N/100 g) increased to a higher level during ice storage than for haddock (18.7 mg N/100 g.).

Microbiological evaluation of the skin and flesh of the two fish species were carried out using various media (LH, 1% NaCl; IA 1% NaCl, and CFC). In general, total viable counts (TVC) were higher on spread-plated Long and Hammer´s (LH) medium for both cod and haddock. Spread-plating of iron agar (IAS) showed higher total counts and predominantly higher counts of H2S-producers than poured iron agar (IAP) with an overlay. At the end of the trial, 40% of the skin micro flora of haddock comprised Pseudomonas group I-II, 20% Shewanella putrefaciens, 15% Aeromonas-like spp. and 10% for Pseudomonas group III-IV spp. While on the flesh, 32% of the micro flora comprised Vibrio/ Photobacterium. The rest of the flesh micro flora was difficult to cultivate and was therefore lost.