Comparison of polyphenols in Goji (Lycium barbarum L.) leaves at different leaf positions under different extraction methods

Goji (Lycium barbarum L.) also known as wolfberry, is one of important medicinal plants in China that has been in use for its medicinal properties and as food supplement for centuries. The abundant bioactive compounds in its fruit, leaves, and root bark are considered beneficial to human health. Phenolic compounds were extracted from different locations of Goji leaves, including tip bud leaves (GBL), young leaves in the middle (GYL), and old leaves at the base (GOL). The phenolics from Goji leaves using ethanolic condensation backflow extraction (EE), ultrasonic extraction (UE), and enzymatic extraction (ME) were prepared, and their polyphenol concentration and antioxidant ability were analyzed. Polyphenol in Goji leaf varied with different positions and extraction techniques. Total 47 phenolic compounds were identified by HPLC-MS, including 43 in GBL, 38 in GYL, and 26 in GOL. Chlorogenic acid, hyperoside, and rutin were the main phenols in Goji leaves, and the highest content of chlorogenic acid in GBL-UE was 2105.05 ± 77.25 µg /g. All Goji leaves showed significant antioxidant effect and polyphenol content, especially GBL that having the highest phenolic level and the stronger antioxidant capacity. Different extraction methods for different leaf positions could improve the extraction efficiency, UE and ME were found suitable for extracting GBL and GOL samples; EE and UE were suitable for extracting GBL samples. GBL exhibited better phenolics and better antioxidant attributes, which are suitable for the development of nutraceuticals and skincare products.