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.