A Novel Method to Extract Juglone from Juglans mandshurica Waste Branches Using a Water-in-Oil Microemulsion

Pruning of Juglans mandshurica produces many branches, which are potentially a rich source of juglone although they are usually discarded as waste. Herein, we describe a water-in-oil microemulsion-based microwave-assisted extraction (MBMAE) method to isolate the juglone found in waste branches from J. mandshurica . In our experiment, J. mandshurica waste branch powder was added to the MBMAE system. Using the optimized microemulsion system comprising Tween 80: n -propanol: n -hexane:water at 27:13.5:4.5:55 (w/w/w/w), and a pH of 5.6, at an operating temperature of 40 °C, operating time of 63 s, and operating power of 400 W, the juglone yield was 4.58 mg/g from a ratio of microemulsion to branch power of 20:1 (mL/g). The juglone extraction yield using the MBMAE method was 1.86- and 6.65-fold better than that obtained from microwave-assisted extraction by ethanol (Ethanol-MAE) and heat reflux extraction by ethanol (Ethanol-HRE), respectively. The MBMAE method may be useful as an alternative to traditional extraction methods to isolate juglone. Graphic Abstract