Photocatalytic Processes in Aquaculture: Effects on Microbial Contamination and Shelf-life in Rainbow Trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) is a highly valued species in aquaculture, appreciated for its nutritional benefits, particularly omega-3 and omega-6 fatty acids. However, microbial contamination and spoilage significantly affect its shelf life and quality. This study investigates the effects of photocatalytic processes on microbial contamination and the shelf life of rainbow trout reared in an innovative aquaculture system. Trout samples were grown in tanks equipped with a photocatalytic system (treated) and standard tanks (control) at the Istituto Spallanzani in Milan, Italy. Fresh samples were analyzed to determine the initial contamination, while frozen–thawed samples were assessed for shelf life over a period of 16 days, evaluating microbiological and sensory characteristics. Microbiological analysis included the use of several agar media, such as PCA, CFC, BPA, Iron agar, and VRBG, to isolate and quantify bacterial species like Pseudomonas, Staphylococcus, Listeria, and Enterobacteriaceae. DNA sequencing, particularly targeting the 16S rRNA gene, was employed to characterize and identify the isolates. Results revealed that treated and control samples showed similar microbial loads, with very low initial contamination as described by total microbial counts (TMC) and total psychrotrophic counts (TPC). The shelf life determined by specific spoilage microorganisms and the sensory analysis of frozen–thawed samples showed odor, texture, and color stability similar between treated and control samples and consistent with literature data. These findings demonstrate that photocatalytic processes did not alter the quality and safety aspects of the final products, offering promising applications for sustainable aquaculture by reducing the risk of pathogens in fish and maintaining the same characteristics in the final products.