Freezing Efficiency and Quality Attributes as Affected by Voids in Plant Tissues During Ultrasound-Assisted Immersion Freezing

Abstract

Voids, filled with air, in plant tissues, can attenuate ultrasound, resulting in weakening the effectiveness of ultrasound during immersion freezing. The effect of voids on ultrasound-assisted immersion freezing (UF) in selected plant tissues, apple, radish, and potato was investigated in the present study. The freezing time and quality attributes of firmness, drip loss, total calcium content, and total phenolic content were investigated in apple, radish, and potato samples treated by normal immersion freezing (IF) and UF. The results showed that the more the percentage voids in the plant tissues, the lower the effectiveness of the ultrasound treatment. The total freezing time reduction (%) due to UF was a power function of the volume of voids (%): y = 0.018x−1.057 (R2 = 0.994). Ultrasound at 0.62 W/cm2 (28 kHz) resulted in the best firmness and lowest drip loss in potato, while no significant (p > 0.05) differences in quality attributes were observed between IF and UF in apple samples. These findings indicated that UF was more effective in freezing fruit or vegetables with a highly dense structure.