Abstract: 【Objective】This study was aimed to investigate the effects of four different drying processes, including hot air drying (HAD), vacuum heat drying (VHD), microwave drying (MD), and vacuum-freeze drying (VFD), on polyphenols content and antioxidant activities of blueberry leaves, which would provide scientific basis for the comprehensive utilization of blueberry leaves.【Method】The phenolic compounds were determined by Folin-Ciocalteu, NaNO₂-Al(NO₃)_3, and HPLC methods, respectively. Meanwhile, the DPPH radical scavenging capacity, FRAP (ferric reducing antioxidant power), and ABTS⁺· scavenging capacity of the extracts of dry blueberry leaves were determined. The relationship between phenolic compounds and antioxidant activity were also analyzed by correlation analysis. 【Result】The total phenol, chlorogenic acid, and rutin contents were varied significantly in blueberry leaves with different drying methods. The VFD blueberry leaves displayed the highest total phenols (55.7 mg GAE·g^-1 DW) and total flavonoids (104.8 mg RE·g^-1 DW) contents, which were 1.2 times higher than that in MD blueberry leaves, and 3 times higher than that in HAD or VHD blueberry leaves. Additionally, the chlorogenic acid (38.3 mg·g^-1) and rutin (10.2 mg·g^-1) in VFD blueberry leaves were also significantly higher than others, which were 1.5 times higher to MD and 2-6 times higher to HAD or VHD blueberry leaves. Moreover, VFD blueberry leaves showed the strongest antioxidant activity, with the median elimination concentration (EC₅₀) of DPPH and ABTS⁺ radical scavenging capacity at 54.8 µg·mL^-1 and 183.9 µg·mL^-1, respectively, and the FRAP value up to 6.0, the antioxidant activity of VFD blueberry leaves was little bit higher than the MD blueberry leaves (EC₅₀ of DPPH· and ABTS⁺· were 61.8 µg·mL^-1 and 225.7 µg·mL^-1, respectively), while the antioxidant activity of MD blueberry leaves was significantly higher than that of HAD (EC₅₀ of DPPH· and ABTS⁺·were 136.6 µg·mL^-1 and 575.1 µg·mL^-1, respectively, FRAP value 1.7) and VHD blueberry leaves (EC₅₀ of DPPH· and ABTS⁺· were 136.1 µg·mL^-1 and 471.3 µg·mL^-1, respectively, FRAP value 1.8) (P＜0.05). No significant difference were observed on the antioxidant activity between HAD and VHD blueberry leaves. In addition to the rutin, the content of other phenolic compounds was significantly correlated with the antioxidant activity (P＜0.01).【Conclusion】The blueberry leaves processed by VFD method retained the highest content of phenolic compounds, antioxidant activity, and reducing power. However, no significant difference was observed between the VFD and MD methods. Thus, our results suggested that one may choose either VFD or MD method to dry blueberry leaves according to the sample quantity and other specific situations.

Key words: blueberry leaf, drying method, phenolic compound, antioxidant activity