Cured or fresh? Between fish maturation trends in restaurants and food safety: The case of dry-aged rainbow trout

Abstract

The application of dry aging on fish is increasing in restaurants worldwide. This process determines fluid loss, changes in muscle texture, and the development of a more concentrated flavour appreciated by consumers. Despite the growing popularity in the foodservice industry, there is a lack of data on potential risks and quality conditions of dry-aged fish. This study was aimed at assessing the safety for consumption of whole rainbow trout subjected to dry aging in a local restaurant (Turin, Italy). Quantitative microbiological analyses and detection of foodborne pathogens were performed on dorsal, ventral muscles, and skin samples at day 0, 3, 6, 10, and 14 of dry aging. Changes in water activity (aw), pH, colour, and biogenic amines in muscle were checked at each sampling point. Almost all the microbiological indicators were below the quantification limits in muscle until day 6 of dry aging, while higher but still acceptable loads were observed at day 10. At day 14, yeasts and moulds exceeded the acceptable level in one case (3.3 ± 0.4 log10 CFU/g) in ventral muscle and counts of Pseudomonas spp. (from 6.1 ± 0.8 to 6.4 ± 0.5 log10 CFU/g), total mesophilic (from 4.4 ± 0.3 to 5.3 ± 0.7 log10 CFU/g), and psychrophilic (from 5.4 ± 0.1 to 5.8 ± 0.3 log10 CFU/g) bacteria indicated the approaching of spoilage. Detection of Listeria monocytogenes and Staphylococcus aureus was always negative during the trials. Minimal changes of pH and colour were observed, while aw values followed a decreasing trend during dry aging. Putrescine was the only detectable amine, with a maximum concentration of 2.05 ± 0.02 mg/kg at day 14. In this study, dry-aged rainbow trout was safe for consumption and 10 days was the most appropriate curing time with 3 °C and 78% of relative humidity. Further studies at different environmental conditions and on other fish species are needed for a comprehensive risk assessment of this fast-growing practice in the restaurant sector.