Photodynamic inactivation as a novel approach for seabass decontamination: effectiveness of TMPyP and methylene blue treatments

Fish is a highly nutritious but perishable food, prone to rapid spoilage due to microbial proliferation and biochemical degradation during handling and storage. Moreover, certain microorganisms can be pathogenic to humans, leading to foodborne diseases. This study presents, for the first time, the efficacy of photodynamic inactivation (PDI) mediated by 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin (TMPyP) and methylene blue (MB) for decontaminating seabass (Dicentrarchus labrax) fillets. The potential of potassium iodide (KI) as an adjuvant to PDI was also investigated. The efficiency of these treatments was assessed in terms of: i) effectiveness against pathogenic bacteria (Escherichia coli and Vibrio parahaemolyticus), ii) reduction of natural microbiota, and iii) ability to extend the shelf life of fish fillets under refrigeration (4 °C). Results show that both TMPyP- and MB-mediated PDI significantly (p < 0.05) decontaminated seabass fillets. MB was the most effective compound, causing approximately 3.0 log CFU.g⁻¹ reductions of E. coli, V. parahaemolyticus, and the natural microbiota. However, the application of KI did not improve the treatments’ effectiveness. MB-mediated PDI also extended the microbiological shelf life of seabass fillets by keeping microbial and trimethylamine-nitrogen (TMA-N) levels within acceptable limits for up to 6 days under refrigeration. On the other hand, untreated samples remained acceptable for only 2 days. Furthermore, the PDI treatment did not affect the lipid content or fillets quality. In conclusion, this study highlights MB-mediated PDI as a promising strategy for the decontamination and microbiological shelf-life extension of fish fillets, providing a potential approach to enhance food safety.