Steam blanching and ethanol pretreatment enhance drying rates and improve the quality attributes of apple slices via microstructure modification

The effect of steam blanching (SB) and ethanol pretreatment (EP) (75-95% [v/v], 10-25 min) on the drying characteristics and quality attributes of apple slices with hot air drying (HD) (60 degrees C, 1.5 m/s) was evaluated. The drying time was reduced by 10.71% and 19.64-47.32% with SB and various EPs compared with fresh; the drying rate and effective moisture diffusion coefficient significantly accelerated. EP resulted in a higher water loss and solid loss of the apple samples. Furthermore, EP greatly affected the rehydration rate and microstructure of dried apple slices. In addition, SB and EP played a positive role in improving the quality of dried apple slices, particularly a higher phytochemical concentration, and antioxidant activities compared with fresh, and EP groups exhibited higher retention of phenolic compounds. Besides, all the dried apple slices with SB and EPs showed a brighter color than the fresh. Therefore, SB and EP can be used as appropriate pretreatment methods for the HD of apples. This combination of the two pretreatment methods provides a theoretical basis for the pretreatment technology before drying of apple and broadens the train of thought in the selection of osmotic media. Novelty impact statement Steam blanching and ethanol pretreatments contribute to the drying rate and quality of apple slices. The pretreatments of E85T25 and E95T25 significantly shorten the drying time, E95T25 shows the highest retention of phenolic compounds, and E85T25 shows the highest phytochemical concentration. E85T25 and E95T25 are suitable pretreatment methods for the HD of apple slices.