Effect of ultrasound irradiation on some freezing parameters of ultrasound-assisted immersion freezing of strawberries

• Ultrasound irradiation applied at any temperature was able to induce nucleation at lower degree of supercooling.
• The supercooling degrees in ultrasound irradiated samples were linearly related to the ultrasound irradiation temperatures.
• Ultrasound irradiation at −1.6 °C significantly lowered the characteristic freezing time of strawberries.
• Ultrasound intensity when applied at higher magnitude was very effective in shortening the characteristic freezing time.

In this study, the effect of ultrasound irradiation temperature and ultrasound intensity on the freezing and nucleation in strawberry samples was studied. The application of ultrasound irradiation at different temperatures was able to induce nucleation at lower degree of supercooling compared to the control samples. The achieved degree of supercooling in the ultrasound irradiated strawberries was linearly correlated to the ultrasound irradiation temperature. At the ultrasound irradiation temperature of −1.6 °C, the characteristic freezing time (CFT) was significantly shorter than that in the control sample (p < 0.05). The application of ultrasound at higher intensities was found to effectively shorten the CFT. The degree of supercooling in ultrasound irradiated samples was not linearly correlated to ultrasound intensity. In conclusion, the combination of ultrasound irradiation temperature and intensity can be effective in controlling nucleation and freezing processes of perishable fruits such as strawberry.