Sodium carboxymethyl cellulose coating pretreatment combined with multi-frequency ultrasound assisted vacuum far-infrared drying: An emerging approach to enhance drying characteristics, physicochemical properties, and sensory attributes of Cornus off

To enhance the drying efficiency and improve the sensory quality of Cornus officinalis, this study investigated the effects of sodium carboxymethyl cellulose (CMC-Na) coating combined with multi-frequency ultrasound assisted vacuum far-infrared (MFUS-VFIR) drying on its drying characteristics, physicochemical properties, and sensory attributes. Application of multi-frequency ultrasound (MFUS) during VFIR dehydration shortened the drying time by 12.12-39.39 % and increased the average drying rate by 15.38-69.23 % compared with VFIR alone. Physicochemical analyses revealed that the (MFUS-VFIR)-20/28/40 kHz treatment yielded dried products with higher retention of total phenolics, natural bioactive compounds, organic acids, total carotenoids, ascorbic acid, soluble solids, and total flavonoids, along with superior color quality. Under these conditions, antioxidant capacity increased by 10.89-23.68 %, 14.41-25.91 %, and 7.10-58.32 %, respectively, relative to dual-frequency ultrasound treatments. Scanning electron microscopy showed that MFUS treatment produced distinct honeycomb-like pores with larger apertures compared with SFUS, indicating reduced surface cracking and expanded micro-channels for mass transfer, thereby lowering mass transfer resistance. The overall sensory acceptability of (MFUS-VFIR)-20/28/40 kHz dried products reached 8.50, representing a 41.67 % and 13.33-30.77 % improvement over VFIR and SFUS-VFIR samples (P < 0.05), with lower bitterness and off-flavor scores. Principal component analysis (PCA), hierarchical cluster analysis (HCA), and correlation network heat mapping revealed that MFUS-treated samples clustered closely in multidimensional quality space and exhibited significant positive correlations with antioxidant activity, physicochemical quality, and flavor retention. Notably, the energy consumption of (MFUS-VFIR)-20/28/40 kHz treatment was 88.68 kW·h·kg^-1, slightly higher than that of the control and SFUS-VFIR treatments. These findings provide a scientific basis and technical reference for quality optimization, energy-efficient drying, and high-value utilization of Cornus officinalis.