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Abstract
High-voltage electrostatic field assisted freezing (HVEF) and freeze-thaw (H-FT) pretreatment were conducted before the microwave freeze drying to improve the quality of freeze-dried hawthorn. The hawthorn samples were frozen at electric field intensities of 0, 1, 3, and 5 kV/cm (C, HVEF1, HVEF3, and HVEF5, respectively), and freeze-thawed in one to three cycles (H-FT1, H-FT2, and H-FT3, respectively) under the selected electric field intensity of 3 kV/cm. The control group was freeze-thawed in two cycles and without electric field treatment (CFT2). The results showed that the drying time of HVEF- and H-FT-treated hawthorn was reduced by 8–25% compared with that of the untreated hawthorn. The HVEF and H-FT pretreatments also affected the quality of hawthorn. Among the samples treated with HVEF, the total phenolic content of HVEF3 samples was the highest (46.31 mg GAE/g), followed by that of HVEF5 (41.87 mg GAE/g) and HVEF1 (37.25 mg GAE/g) samples. Similarly, among the samples treated with H-FT, the total anthocyanin content of H-FT2 samples was the highest (1.50 mg C-3-G eqiv/g), followed by that of H-FT1 (1.34 mg C-3-G eqiv/g) and H-FT3 (0.87 mg C-3-G eqiv/g) samples. Additionally, the H-FT2 treatment led to higher hardness (16.60 N), rehydration capacity (3.47 g/g), and total phenolic content (38.19 mg GAE/g) than the CFT2 treatment. In conclusion, H-FT2 improved the quality of hawthorn. This study lays a foundation for producing high-quality dried hawthorn using H-FT pretreatment, reducing the drying time and thereby improving drying efficiency.
Disclosure statement
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.