Abstract: This study aimed to explore the effect of different drying methods: sun drying, hot air drying, short- and medium-wave infrared drying, freeze drying and pulsed vacuum drying on the drying characteristics, color, phenolic acid contents, and antioxidant activity in vitro of rape bee pollen. The relationship between microstructure and quality changes was investigated as well. The results showed that the fastest drying rate was observed with infrared radiation drying. Sun drying took the longest time, and resulted in the severest color deterioration. Among the five drying methods, rape bee pollen subjected to pulsed vacuum drying had the highest ferric ion reducing antioxidant power (FRAP) ((1 961.11 ± 4.42) mmol/g), which was 24.78% higher than that of fresh rape bee pollen, and it also had the lowest ΔE value (0.98 ± 0.04). Besides, FRAP and the contents of chlorogenic acid, vanillic acid and sinapic acid in rape bee pollen were significantly after drying (P < 0.05), while no significant change was observed in the content of p-coumalic acid. Correlation analysis showed that the content of p-coumalic acid was significantly negatively correlated with ΔE (P < 0.05) but positively correlated with L* value (P < 0.05). Clustering analysis showed that the similarity between sun drying and four other drying methods was 0. The similarity between hot air drying and infrared radiation drying was 84.11%. The differences between these five drying methods were clearly determined by clustering analysis (CA) and principal component analysis (PCA). Collectively, pulsed vacuum drying can protect the microstructure and color of rape bee pollen at low drying temperature (45 ℃) while significantly increasing the contents of chlorogenic acid, vanillic acid and sinapic acid and antioxidant activity (P < 0.05), suggesting its great potential in drying bee pollen.

Key words: drying methods; rape bee pollen; color; phenolic acids; antioxidant activity; microstructure