Effect of multi-mode dual-frequency ultrasound pretreatment on the vacuum freeze-drying process and quality attributes of the strawberry slices

• Main Authors: Baoguo Xu, Jianan Chen, Essodézam Sylvain Tiliwa, Weiqiang Yan, S.M. Roknul Azam, Jun Yuan, Benxi Wei, Cunshan Zhou, Haile Ma
• Format: Article
• Language: English
• Published: Elsevier 2021-10-01
• Series: Ultrasonics Sonochemistry
• Subjects: Ultrasonic; Strawberry; Vacuum freeze-drying; Water migration
• Online Access: http://www.sciencedirect.com/science/article/pii/S135041772100256X

The effects of osmotic pretreatment assisted by ultrasound in different frequency modes before vacuum freeze-drying (VFD) on moisture migration and quality characteristics of strawberry slices were investigated. The frequency modes are single-frequency modes under 20, 40 kHz (SM-20, SM-40), and dual-frequency under 20/40 kHz including sequential mode (SeDM) and simultaneous mode (SiDM). The quality characteristics of dried strawberry products including rehydration, hardness, color, flavor, total anthocyanins, total phenols, vitamin C content, and active antioxidant components (DPPH and –OH) were determined. Results showed that drying time of the strawberry slices irradiated by ultrasound was reduced by 15.25%–50.00%, compared to the control samples. Besides, dual-frequency ultrasound shortened the drying time more than single-frequency ultrasound. The drying time of SeDM was the shortest. In addition to vitamin C content, the quality characteristics including rehydration, hardness, color, flavor, total anthocyanins, total phenols, and antioxidant activity of dried strawberry products pretreated by SeDM were significantly (p < 0.05) better than those of control and other pretreated samples. It can be concluded that the SeDM was an effective pretreatment method to produce high-quality vacuum freeze-dried strawberry products.