Ultrasound-assisted supercritical carbon dioxide drying of cod fish (Gadus morhua)

Supercritical CO2 (scCO2) drying has emerged as a promising alternative to reduce water content at low temperatures and simultaneously inactivate microorganisms, thus increasing product safety while preserving product quality. In this study, scCO2 drying was applied to cod fish samples at 40°C and 10 MPa for 360 min alone and in combination with high power ultrasound (HPU). Results were compared with traditional air drying at 40 and 60°C. The drying rate for the scCO2 was similar to that of air drying at 40°C while adding HPU induced a higher water loss comparable to air drying at 60°C, reaching a final water activity of 0.565 ± 0.051. The inactivation of E. coli and L. innocua was possible for both scCO2 treatments, achieving a complete inactivation (> 5-log reduction) after 60 min of treatment. No significant inactivation was achieved with air drying, even at 60°C. ScCO2 and scCO₂ + HPU-dried samples exhibited higher specific volume, lightness, porosity, wettability, rehydration capacity, and improved texture compared to air-dried samples. Overall, these findings demonstrate the feasibility of using scCO2 to produce a microbiological safer dried fish product with higher quality compared with traditional air drying and that the combination with HPU can accelerate the process without side effects on the product. Future work shall focus on the evaluation of sensory quality, consumer acceptance, and the preservation of key nutritional attributes during storage to further support industrial applications.