A study on the visualization of ultrasound-assisted thawing process of frozen carrots using an in-situ schlieren imaging system

Abstract

Background

The thawing process is a crucial step before consuming frozen food. This study uses an in-situ schlieren imaging system to visualize fluid dynamics during the ultrasound-assisted thawing of frozen carrots.

Method

The schlieren images from three thawing stages are analyzed using the optical flow method to extract velocity vector fields at different thawing heights and power levels. The effects of ultrasound-assisted water thawing (UWT) on thawing time and quality attributes of carrot are compared with those of other thawing methods, including air thawing (AT), refrigerated thawing (RT), microwave thawing (MT), and water thawing (WT).

Results

The results indicate that in fluid dynamics visualization, turbulence velocity peaks during the preheating stage and gradually declines as thawing progresses. Increasing thawing height improves WT efficiency for frozen carrots but reduces UWT efficiency. Higher UWT power levels generally boost flow field velocity, enhancing thawing efficiency. Therefore, 10 cm is considered the optimal thawing height for UWT, and 180 W is identified as the optimal power in this study. UWT significantly shortens thawing time compared to other methods (P < 0.05), with the highest retention of color and vitamin C, and minimal microstructural damage.

Conclusion

UWT can serve as an effective method to accelerate the thawing process of frozen carrots, and schlieren imaging can be instrumental in aiding the exploration of its fluid dynamics and heat transfer mechanisms in water.