Microbial contamination in PUR- and PE- insulated fish tubs

Abstract

Fish tubs or fish totes are insulated plastic containers used for storing and transporting fresh fish from onboard fishing trawlers to fish markets and fish processing factories. These tubs are three-layered with a polyethylene (PE) shell on the inside and outside. The middle layer is the insulation and it is either made of polyurethane (PUR) or polyethylene (PE) foam. Along with fresh fish the tubs are typically filled with flake ice or slurry ice for preservation and to minimize microbial growth.The aim of this study was to assess insulated fish tubs currently in commission with regards to microbial contamination and food safety, through sampling, cultivation and microbial diversity analysis with 16S rRNA amplicon sequencing. A secondary objective was to compare the two different insulation materials (PUR and PE) if exposed by wall damage and explore whether the type of insulation had any significant effect on water content supporting microbial growth.Results from the cultivation revealed that rental fish tubs in commission had total viable counts (TVC) in the range of 10^5-10`7 cfu/ml, but after cleaning of those tubs the counts had dropped to the range of 10^3-10^5 cfu/ml. Analysis of the bacteria composition of the rental tubs revealed a high relative abundance of a few spoilage organisms, like Brochothrix thermosphacta, Pseudomonas, Psychrobacter and Carnobacterium but no pathogenic bacteria were identified. After cleaning of the tubs there was a decrease in Carnobacterium but the changes in relative abundance of other spoilage organisms varied between fish tubs.Additionally, the study showed that a recently decommissioned fish tub with PUR insulation had visible water travelling within the insulation and had a TVC of 10^5 cfu/ml while no water was detected in the PE insulated tubs. Presence of bacteria in the water within the damaged tubs might be a source of dissemination of undesirable microbes and therefore decrease food safety.