Effects of tri-frequency ultrasonic vacuum-assisted ethanol pretreatment on infrared drying efficiency, qualities and microbial safety of scallion stalk slices

This paper aims to evaluate the impact of simultaneous tri-frequency ultrasound (20 + 40 + 60 kHz) combined vacuum (0.6 bar) assisted ethanol (75%) pretreatment on the infrared drying process, qualities (rehydration, flavor, surface color), and microbial safety of scallion stalk slices. The slices were pretreated with different methods, using ethanol, vacuum (Water + VC), vacuum-assisted ethanol (Ethanol + VC), ultrasound (Water + US), ultrasound-assisted ethanol (Ethanol + US), ultrasonic vacuum (Water + USVC), and ultrasonic vacuum-assisted ethanol (Ethanol + USVC). It was found that Ethanol + USVC pretreatment significantly reduced the drying time and showed better flavor retention and antibacterial effect, and the slices produced showed moderate rehydration ratio (7.83) and surface color change (8.94).

Automated summary

This study evaluated the impact of simultaneous tri-frequency ultrasound combined vacuum assisted ethanol pretreatment on the drying process, qualities, and microbial safety of scallion stalk slices. The Ethanol + USVC pretreatment significantly reduced drying time, retained flavor, and exhibited antibacterial effects, resulting in slices with moderate rehydration ratio and surface color change.