Effects of power ultrasound on immersion freezing parameters of potatoes

Ultrasound has attracted great interest in recent years and its application in food freezing has shown promising advantages. In the present study the application of ultrasound during immersion freezing of potato cubes was studied and particular attention was given to the effects on supercooling process. Ultrasound, produced through a 35 kHz sonotrode, was applied when the temperature in the geometrical center of potato sample was in the range from − 0.1 to − 3.0 °C. Several freezing parameters, as nucleation temperature and time, supercooling, initial freezing temperature, transition phase and global freezing duration, were evaluated and discussed.A significant anticipation of nucleation was detected when the ultrasound application temperature was lower than − 0.1 °C; moreover it was found a linear correlation between ultrasound irradiation temperature and supercooling reached in potato samples; finally a reduction in freezing time was recorded when ultrasound was applied at − 2.0 °C.Industrial relevanceUltrasound has acquired relevance in several industrial sectors, including food science and technology. In the present investigation power ultrasound has been studied in assisting and accelerating immersion freezing of potato cubes, obtaining promising results. In fact it was found that ultrasound was able to induce nucleation in the centre of potato cubes, interrupting the supercooling process. Moreover, under particular operative conditions, the freezing time of ultrasound-assisted potato cubes was significantly reduced with respect to non–irradiated samples. The results achieved demonstrate that the application of power ultrasound during immersion freezing has a great potential in the control of the freezing process. In particular the possibility of reduction of the freezing time and costs, as well as the influence of ultrasound on quality, stability and sensory properties of frozen food have a crucial importance to food industry and have to be widely investigated.

► The effect of ultrasound on immersion freezing of potato cubes was studied.
► Ultrasound was applied above and below the freezing point of potatoes.
► Power ultrasound was able to anticipate the beginning of nucleation.
► Supercooling degree was linearly related to ultrasound irradiation temperature.
► When ultrasound was applied at − 2 °C the shortest freezing time was achieved.