The effect of different blanching treatments on the quality of hot-air drying apple slices was investigated in this research. The fresh-cut apple slices were treated by hot water blanching, steam blanching and microwave blanching respectively. After blanching and hot-air drying, the color, polyphenol content, composition and antioxidant activity of apple slices were evaluated. The results showed that the drying time of apple slices blanched in hot water was the shortest, which was 270 min. The browning characteristics of apple slices were significantly affected by different blanching methods (P<0.05). The color change of apple slices treated by hot water blanching was the least, while that of apple slices treated by microwave blanching was the highest. Compared with fresh samples, blanching methods had little effect on reducing the sugar content of apple slices. While, the content of 5-hydroxymethylfurfural produced in apple slices treated by microwave blanching was the highest, followed by steam blanching and hot water blanching. The loss of vitamin C in apple slices after hot water blanching and drying were 34% and 52%, respectively. The content of total phenol was the highest in apple chips treated by hot water blanching, which reached 11.82 mg GAE/g DW. There were no significant changes in the content of free polyphenols and bound polyphenols in apple slices after blanching treatment (P>0.05). However, the content of bound polyphenols in all samples was significantly increased (P<0.05) after hot air drying, while the content of free polyphenols was not significantly changed (P>0.05) which indicating that the three blanching treatments were beneficial to the retention of polyphenols. The antioxidant capacity test of polyphenols showed that the antioxidant activity of the bound polyphenols changed significantly in apple slices after blanching and drying, and the bound polyphenols of apple slices were treated by hot water blanching had the highest antioxidant activity. In conclusion, hot water blanching is more beneficial to reduce browning and improve the antioxidant activity of apple slices, while steam blanching and microwave blanching are more beneficial to retain nutritional components.
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