CO05 | HISTAMINE ACCUMULATION IN READY-TO-EAT SALMON PRODUCTS SUPPLEMENTED WITH ANTI-LISTERIAL LACTIC ACID BACTERIA: AN OVERLOOKED FOOD SAFETY RISK?

Luca Nalbone¹, Salvatore Pennisi¹, Federica Spinola², Graziella Ziino^1|2, Alessandro Giuffrida^1|2 | ¹Dip. Scienze Veterinarie, Uni. Messina, Messina, Italy; ²Riconnexia srls, Dip. Scienze Veterinarie, Uni. Messina, Italy.

Aim. Salmon (Salmonidae) does not belong to the fish families with naturally high free histidine content for which European legislation sets a histamine limit and is therefore not regarded as a histamine-risk product. Nonetheless, histamine accumulation has been reported in some salmon products, and it has been hypothesised that the lactic acid bacteria (LAB) cultures intentionally added to such products to control Listeria monocytogenes growth could contribute to its formation. This study assessed whether adding LAB cultures favours hazardous histamine accumulation in ready-to-eat (RTE) salmon products during commercial shelf life.

Methods. Six commercial RTE salmon products (smoked salmon, carpaccio, tartare) were studied: three supplemented with LAB cultures and three comparable products without added cultures. Samples were stored at 7 °C to mimic domestic temperature abuse and analysed at fixed times throughout shelf life for spoilage and hygiene microbiota (mesophilic LAB, Enterobacteriaceae, Pseudomonas spp., yeasts, moulds), sensory quality, histamine quantification, pH and water activity (aw). Microbiological, sensory and physico-chemical analyses were performed according to ISO standards; histamine was quantified by high-performance liquid chromatography (HPLC).

Results. Small amounts of histamine formed in all products, but hazardous levels were reached only in the three supplemented with LAB cultures. In smoked salmon, histamine rose from undetectable to 91 mg/kg by day 8 and 322 mg/kg by day 23, reaching 716 mg/kg at the end of shelf life (day 45), when the product was still organoleptically acceptable. Carpaccio and tartare exceeded 400 mg/kg by day 23, with sensory changes only beginning to appear. In these products mesophilic LAB reached 8.10-8.72 log CFU/g, while Enterobacteriaceae remained 2-3 log CFU/g (peak 3.45 CFU/g) and Pseudomonas spp. did not exceed 3.9 log CFU/g. The products without added cultures kept histamine below 15 mg/kg, with native LAB up to 8.1 log CFU/g, Enterobacteriaceae undetectable and Pseudomonas spp. up to 4.3 log CFU/g. Moulds were undetectable in all products throughout shelf life. Yeasts stayed below 3.1 log CFU/g in the LAB-supplemented products but reached higher counts in the controls, up to 5.9 log CFU/g in one carpaccio. Mean pH and aw were 5.95/0.961 for smoked salmon, 5.86/0.960 for carpaccio and 5.81/0.968 for tartare.

Conclusions. Hazardous histamine concentrations developed in salmon products, a foodstuff neither legally subject to histamine limits nor routinely tested for it, and only where anti-listerial LAB cultures had been added. Interestingly, peak histamine coincided with low levels of the classic histamine-forming flora (especially Enterobacteriaceae) and with still-acceptable organoleptic quality. The underlying mechanism remains to be clarified: the added culture may be proteolytic and decarboxylase-positive, releasing histidine and itself converting it into histamine; alternatively, proteolytic LAB may liberate histidine that low-level decarboxylating bacteria then convert into histamine. Either way, these findings reveal a potentially underestimated food safety risk not covered by specific regulatory limits; it may be speculated that bioprotective cultures should be screened for histidine-decarboxylase and proteolytic activity, and histamine monitored, in this product category.