Objective  This project investigated the extraction process of Morus alba leaf flavonoids and their free radical scavenging ability, inhibition of α-glucosidase and α-amylase activity, aiming at obtaining a novel preparation method that fully maintained the activity of Morus alba leaf flavonoids, and providing a theoretical basis for the development and utilization of Morus alba leaf resources.

  Method  The ultrasonic-semi-bionic method was used to extract the flavonoids from the Morus alba leaves. We investigated the effects of four factors (liquid-to-material ratio, ultrasonic time, ultrasonic temperature, and ultrasonic power) on the yield of Morus alba leaf flavonoids and the average scavenging of DPPH· and OH· radicals. The extracting process was optimized using the response surface test to evaluate the inhibitory effects of Morus alba leaf flavonoids on α-glucosidase and α-amylase.

  Result  Optimal extraction conditions of Morus alba leaf flavonoids were as follows: ratio of liquid to solid was 30 mL/g, ultrasonic time was 97 min (the time ratio of the three stages was 1∶2∶2), ultrasonic temperature was 49 ℃, ultrasonic power was 400 W. Under conditions, the flavonoid yield up to (38.23 ± 0.42) mg/g was obtained with an average clearance rate of (57.04 ± 0.97) %. Under optimal conditions, the IC₅₀ value for α-glucosidase inhibition by Morus alba leaf flavonoids was (1.081 ± 0.130) g/L, and that for α-amylase inhibition was (1.204 ± 0.190) g/L. The free radical scavenging ability of Morus alba leaf flavonoids extracted by ultrasonic-semi-bionic method was stronger than that of the ultrasonic method, and the yield of Morus alba leaf flavonoids extracted by ultrasonic-semi-bionic method was higher than that of the semi-bionic method.

  Conclusion  Morus alba leaf flavonoids extracted by ultrasonic-semi-bionic method have good free radical scavenging ability and inhibitory effect on α-glucosidase and α-amylase. Compared with the single extraction method, the Morus alba leaf flavonoids extracted by ultrasonic-semi-bionic method have higher bioactivity and yield. Morus alba leaf flavonoids can be developed as blood glucose regulating products for people with high glucose levels, and the ultrasonic-semi-bionic method can provide a better technical reserve for the industrial preparation of Morus alba leaf flavonoids.