Abstract
Microbial (colony counts, 16S rRNA gene amplification), chemical (pH, 1H NMR spectroscopy) and sensory changes in raw Atlantic Salmon (Salmo salar) and tuna (Thunnus albacares) fillets stored under vacuum at 3 °C were evaluated over a period of 12 days. Both species of fish are globally important and among the ten most consumed fishes in the world. Although the sensory analyses showed a decrease in the quality of both fish species, only the salmon fillets were considered spoiled at the end of the storage period. In salmon, trimethylamine was the main spoilage product and bacterial colony counts reached an average of 7.3 log10 cfu/g. The concentration of glucose decreased and the concentration of organic acids increased during storage revealing glucose fermentation. Photobacterium was the dominating genus in the salmon studied. In the tuna studied, the bacterial colony counts reached only an average of 4.6 log10 cfu/g. The dominating bacteria in tuna were Pseudomonas spp. Glucose levels did not decrease, suggesting that amino acids and lactate most likely acted as carbon sources for bacteria in tuna. In conclusion, the study revealed that salmon was clearly a more perishable fish than tuna.
Highlights
Fish are among the healthiest foods and provide us with valuable unsaturated and omega-3 fatty acids
Microbiological analysis, pH and amplicon sequencing On the day of arrival, total psychrotolerant bacterial counts were between log 3 and log 4, indicating good microbial quality of the fish (Fig. 1)
The bacterial counts of vacuum packaging (VP) tuna reached their maximum level on day 9, but only a 0.5 log increase was observed
Summary
Fish are among the healthiest foods and provide us with valuable unsaturated and omega-3 fatty acids. They are one of the most perishable food items. It is estimated that 30% of fish landed/caught is lost through microbial activity alone (Amos, 2007). Microbial spoilage proceeds fast because of the presence of large amounts of low-molecular-weight compounds, high water activity and high post-mortem pH (>6) in fish muscles. Refrigeration is necessary to extend the shelf-life of fish and is often combined with vacuum packaging (VP) to restrict the growth of aerobic spoilers (Dalgaard et al, 1993; Goulas and Konominas, 2007; Silbande et al, 2016)
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