Evaluation of sensory and microbiological changes and identification of proteolytic bacteria during the iced storage of farmed turbot (Psetta maxima)

Sensory and quantitative microbiological analyses were performed in farmed turbot (Psetta maxima) during iced storage. Sensory analyses revealed a shelf life of 19 d for farmed turbot. The production of total volatile base nitrogen (TVB-N) and trimethylamine-nitrogen (TMA-N) was low and reached levels close to 40 mg TVB-N/ 100 g muscle and 3.5 mg /TMA-N/100 g muscle, even after 40 d of refrigerated storage. The pH value of turbot muscle increased from an initial value of 6.3 to close to 7.0 after 29 d of iced storage. Microbial growth was slow in iced turbot: total aerobic counts reached levels below 7 log colony forming units/g units even after 40 d of storage. Lactic acid bacteria-mainly Lactobacillus delbrueckii subsp. delbrueckii and Lactococcus lactis subsp. lactis strains-were predominant among the proteolytic strains isolated from iced turbot. Proteolytic strains of L. lactis subsp. lactis, Brochothrix thermosphacta, Plesiomonas shigelloides, Proteus vulgaris, and Pantoea species were also isolated from temperature-abused turbot, such proteolytic strains being predominant with respect to nonproteolytic microorganisms, suggesting a preferential role of such proteolytic bacteria in the spoilage of turbot. The slow bacterial growth, together with the relative predominance of lactic acid bacteria over Gram-negative microorganisms, may be related to the extraordinary maintenance of the quality and extended shelf life of farmed turbot.