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

Abstract

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).

Keywords:

• Ultrasonic vacuum
• scallion stalk
• infrared drying
• ethanol pretreatment
• microbial safety

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors are appreciated to the financial support offered by the National Key Research and Development Program of China (NOs. 2017YFD0400903 (01), 2016YFD0400705 (04)), National Nature Science Foundation of China (NO: 31801599), Science and Technology Major Project of Anhui (NO. 18030701152), the Key Research and Development Program of Jiangsu (NO. BE2019366) and 333 high level talents of Jiangsu (NO. 2018-26).