Cavitation-enhanced aroma and browning: A multiscale study of star anise (Illicium verum Hook. f.) pretreated by ultrasound and electrolyzed water

Conventional pretreatments of star anise (Illicium verum Hook. f.) often result in uneven color development, long drying duration and substantial aroma losses, hence limiting final product quality and market value. To address these issues, the present study hypothesized that ultrasound-assisted electrolyzed water thawing (UEWT) as pretreatment prior to drying could accelerate drying and enrich flavor of star anise by inducing appropriate structural and biochemical changes. The effects of UEWT were compared with those of deionized water thawing (DWT), electrolyzed water thawing (EWT), ultrasound-assisted deionized water thawing (UDWT), and hot water blanching (HWB), with a focus on drying kinetics, microstructure, relevant enzyme activities, antioxidant activities and volatiles composition of star anise were evaluated. UEWT reduced drying time to 8 h, with the highest drying rate (0.75 kg/(kg·h)), free water content (48 %) and oil-associated NMR signal (23 %). Enhanced cell disruption enhanced moisture migration and volatiles release, while elevated PPO and POD activities intensified desirable coloration (a* = 27.3; ΔE = 26.8); antioxidants retention was nevertheless compromised (phenolics 45.94 mg GAE/g; flavonoids 2.35 mg GAE/g). UEWT also resulted in the highest content of trans-anethole (1100.40 μg/kg) and formation of α-terpineol, both of which are key contributor to characteristic aroma of star anise. These findings demonstrate that UEWT effectively balances drying rate, color formation, and aroma retention, offering a practical pretreatment for quality-oriented drying of spice fruits. Future studies should optimize ultrasonic parameters and evaluate industrial-scale integration for continuous spice processing.