Effects of ultrasonic and high-pressure processing pretreatment on drying characteristics and quality attributes of Angelica keiskei slices prepared by vacuum-freeze drying

To maximally maintain Angelica keiskei Koidzumi (A. keiskei) quality and reduce drying energy consumption, this study examined the impact of ultrasound (US), high-pressure processing (HPP), and their combination (US-HPP) as pre-treatment on the performance of vacuum freeze drying (FD) A. keiskei slices. During the vacuum FD process, the drying time, moisture content, and water activity of US and US-HPP samples were markedly reduced, while the drying time of HPP samples was increased. In addition, the content of active substances (total flavonoid content, total phenolic content, chalcone content) and antioxidant activity (DPPH, -OH and ABTS radical scavenging activity) of each group of samples were compared. US pretreatment can effectively improve the FD rate; and US-HPP significantly preserves the active substances and antioxidant activity of the sample. Therefore, both ultrasound and the ultrasound-high-pressure processing combination emerge as promising techniques for enhancing the vacuum freeze-drying process of A. keiskei products.