Low-temperature drying of salted cod (Gadus morhua) assisted by high power ultrasound: Kinetics and physical properties

• Power ultrasound (US) was used for improving low-temperature drying of salted cod.
• US quickened the drying kinetics, shortening the drying time by up to 50%.
• The increase in the effective diffusivity produced by US reached 110%.
• US promoted changes in dried-salted cod structure.
• US increased the lightness of dried-salted cod, which is a relevant quality trait.

Low-temperature convective drying could be considered an affordable alternative to conventional freeze-drying for foodstuffs. The process intensification should be based on non-thermal technologies, such as power ultrasound. Thereby, the aim of this work was to evaluate the air-borne application of power ultrasound on the low-temperature drying of salted cod. For that purpose, drying experiments were carried out at − 10, 0, 10 and 20 °C on salted cod slices at 2 m/s with (AIR + US, 20.5 kW/m3) and without ultrasonic application (AIR). In the dried-salted cod, its rehydration capacity was analyzed, as were the microstructural, textural and color changes. At every temperature tested, ultrasound application increased the drying rate; thus, an average increase of 74% was observed in the effective diffusivity. AIR + US dried samples were softer and exhibited a higher rehydration capacity than AIR ones, which was linked to the microstructural changes produced by ultrasound. In addition, color changes were induced by ultrasound application.Industrial relevanceNowadays, low-temperature convective drying represents a promising alternative for the production of high-quality dried products. However, this technology is mostly limited by the low drying rate, which retards the dehydration process and directly increases the processing costs. Power ultrasound, a non-thermal technology, represents an interesting alternative means of improving low-temperature convective drying due to the fact that acoustic (mechanical) waves may affect water removal during drying with a low heating capacity. Thereby, the ultrasonically enhanced low-temperature convective drying could constitute an affordable alternative to lyophilization (or freeze-drying), which is mainly restricted to high-quality food commodities.