Impact of superchilling technique on the microbiological quality of fresh salmon
Résumé
Superchilling is an innovative method for food preservation at temperature between refrigeration and freezing. It addresses the challenges of maintaining food safety while improving process sustainability. Refrigeration increases the shelf life by slowing down or even stopping the growth of spoilage microorganisms. However, it can allow the growth of psychrotrophic bacteria such as the foodborne pathogen Listeria monocytogenes. Freezing stops bacterial growth, but it affects the food organoleptic qualities (texture, water loss, colour). Moreover, long-term storage at negative temperature requires high energy inputs.
The aim of superchilling is to combine the advantages of the two techniques: a longer shelf life compared to refrigerated products, a better preservation of organoleptic qualities and a lower energy consumption compared to freezing.
Superchilling is a two-step technique: an initial pre-freezing phase, and a storage phase at 1 to 2 °C below the initial freezing temperature. The objective of this study is to understand the impact of different conditions of superchilling on the growth of salmon microbiota compared to refrigeration.
Salmon samples were chilled at various temperatures: (i) 2°C, the standard refrigeration temperature used in fish preservation, (ii) -0.8°C, the salmon initial freezing temperature; (iii) −1.8 °C and −2.8 °C, two superchilling temperatures to respectively obtain 30% and 40% ice content. Only the samples stored at the two latter temperatures were subjected to initial pre-frozen step at −23 °C during 13 min. The growth of natural salmon microbiota was followed by plating during 13 days. In parallel, genomic DNA extractions were performed over time to evaluate the evolution of microbiota diversity by 16S rRNA metabarcoding.
The bacterial population of salmon samples increased over time when stored at 2 °C and -0.8 °C. Bacterial diversity decreased over time, probably due to the specific growth ability of psychotropic bacteria. Growth under superchilling conditions at −1.8 °C and −2.8 °C was significantly reduced. This work provides promising results to understand the impact of superchilling on the evolution of salmon microbiota and thus to optimise the management of food quality and safety