A novel method to extract juglone from Juglans mandshurica waste branches using a water-in-oil microemulsion

Pruning of Juglans mandshurica produces a lot of waste branches which are potentially rich source of juglone. However, they are usually discarded as waste. Given that, the water-in-oil microemulsion was proposed, aiming at developing a novel and efficient microemulsion-based microwave-assisted extraction（MBMAE）method. By which juglone in the Juglans mandshurica waste branches could be obtained. In our experiment, the waste branches powder was added to the MBMAE system. Under the best microemulsion system: (tween 80: n-propanol : n-hexane : water＝27% : 13.5% : 4.5% : 55%), the PH of the microemulsion solution of 5.6, microemulsion - Juglans mandshurica branches powder of 20:1 (mL/g), operating temperature of 40°C and operating time of 63 s, operating power of 400 W, the juglone yield was 4.58 mg/g. The results were that the extraction yield applying the MBMAE method were 1.86-fold and 6.65-fold that of microwave-assisted extraction applying ethanol (Ethanol-MAE) and heat reflux extraction by ethanol (Ethanol-HRE), respectively. Obviously, the MBMAE method could be used as an alternative to traditional extraction methods to extract juglone.Statement of Novelty A large number of waste branches from Juglans mandshurica pruning are often discarded as waste. Based on the concept of green development, this work proposes for the first time the extraction and utilization of juglone from the waste branches of Juglans mandshurica. However, a certain problem such as low efficiency, high cost, and complicated operation is existing in traditional extraction method for juglone. Consequently, a special microemulsion system for juglone was established for the first time, and on this basis, the application of MBMAE method to the extraction of juglone was also proposed for the first time. It provides data support for the extraction of juglone from other materials or plants.