Abstract: The traditional seafood soup ‘Fotiaoqiang’ was processed into broth powders by separately using ultrasonic spray-freeze drying (USFD), vacuum freeze drying (FD) and spray drying (SD), and we compared the physicochemical properties and microstructure of the 3 powders. The results showed that the USFD powder had low water content (4.79%), small bulk density (102 mg/mL), small particle size (23.11 μm in average), and good solubility. This powder existed mostly in the form of regular spherical particles with smooth surfaces, good uniformity, controllable size and high porosity, which facilitates the diffusion of moisture from the interior to the exterior of the particles. The FD powder presented various states, such as needle type and flat type. The SD powder particles mostly exhibited an oblate spherical shape. The USFD powder scored 8.8 points in sensory score for flavor, which was more in line with the flavor standard of undried traditional broth. Solid-phase microextraction coupled with gas chromatography-mass spectrometry (SPME-GC-MS) was used to investigate the retention of volatile compounds during the drying process. The results showed that 39 volatile compounds were detected in the USFD sample, including 7 alcohols, 7 aldehydes, 1 ketone, 4 esters, 8 heterocyclics and 12 alkanes. Therefore, USFD could better preserve the overall flavor of the soup.

Key words: ultrasonic spraying-freeze drying, spray drying, vacuum freeze drying, structural properties, volatile components