Effects of different drying processes on the flavonoids characteristics of Guanxi honey pomelo (Citrus grandis (L.) Osbeck) peel by HPLC-Q-TOF-MS analysis

Citrus peels are rich in flavonoids, and some valuable flavonoids with health benefits, such as polymethoxyflavones (PMFs), are found almost exclusively in citrus peels. While the peels usually regarded as by-product, leading to source waste. As a traditional method, drying is helpful to increase added-value of peels which can be used as medicine. However, the variations in variety and quantity of flavonoids during drying processes of citrus peel remain unknown. In this study, Guanxi honey pomelo peel investigated the effect of different drying methods on flavonoids content in citrus peels. Five drying techniques, namely, freeze-drying (FD) and hot air drying (HAD) at 30 °C, 50 °C, 70 °C and 90 °C were used employed for drying the pomelo peels and HPLC-Q-TOF-MS analysis identified 39 flavonoids changes in flavonoids across samples. FD proved to better preserve most glycosidic flavonoids. Flavonoid aglycones could be better preserved in samples of HAD at 30 ℃, 50 ℃ HAD and 90 ℃ HAD. Specifically, HAD at 30 ℃ and 50 ℃ HAD is beneficial for obtaining more valued polymethoxyflavones such as 5-hydroxy-6,7,4′-trimethoxyflavone, 5,7,8,4′-tetramethoxyflavone and 3,5,6,7,8,3′,4′-heptamethoxyflavone. The 90℃ HAD resulted in the highest content of naringenin and 5,7,8,4′-tetramethoxyflavanone. This study demonstrated the transformation characteristics of flavonoids in pomelo peel under varying drying conditions, providing benefits for comprehensive utilization of pomelo peel in extracting valued-added flavonoids.

Graphical abstract