Objective  The solid shell of Quercus mongolica is rich in polyphenols, flavonoids and other active compounds with a variety of functions. In order to further develop Q. mongolica resources and obtain high antioxidant activity and efficient preparation methods, the active components and antioxidant activity of Q. mongolica shell extracts extracted by different methods were compared.

  Method  The contents of total phenols, total flavonoids, total triterpenoids and soluble sugar were determined by spectrophotometry. Fourier transform infrared spectroscopy (FTIR) was used to analyze the functional group changes of the extracts of Q. mongolica with 4 extraction methods.

  Result  There were significant differences in the effects of the four extraction methods on the extraction efficiency and antioxidant activity of Q. mongolica shell, among which enzymatic hydrolysis method had the best extraction effect on phenolic compounds from Q. mongolica shell, and the total phenolic content per 100 g was as high as (1.090 ± 0.570) g. FTIR showed that the absorption peak intensity was the highest at 3401 and 1 039 cm⁻¹, which were the stretching vibration of hydroxyl O−H and C−O−C of phenolic substances, respectively. In vitro antioxidant test results showed that the antioxidant activity of the extract was the strongest. When the concentration of the extract solution was 0.80 g/L, the scavenging rate of ·OH was 98.55%, which was higher than that of VC (82.03%). Correlation analysis showed that polyphenols played a major role in antioxidant activity.

  Conclusion  The active components and antioxidant capacity of extracts extracted by solvent extraction, high shear method, ultrasonic method and enzymatic hydrolysis method were compared. It is found that enzymatic hydrolysis method has the highest content of active substances and antioxidant activity. Therefore, the enzymatic hydrolysis method is an effective method to extract rich antioxidant active substances from Q. mongolica shell, and the enzymatic hydrolysis extraction is simple, low cost, which can be used for the preparation of active substances and natural antioxidant development of Q. mongolica shell. The results of this study provide theoretical basis for the selection of extraction technology of Q. mongolica shell extract and the development and utilization of antioxidants.