Antagonistic mechanism and antioxidant of crude extract of Aspergillus niger xj

The aim of this experiment was to investigate the antioxidant activity and antagonistic mechanism of crude extract SE of Aspergillus niger xj against Sclerotium rolfsii R-67 in Amorphophallus konjac K. Koch. The inhibition of SE on R-67 was studied by the growth rate method. Then the bacteriostatic mechanism of SE was studied by measuring the conductivity, nucleic acid and protein leakage, the specific activity of tricarboxylic acid cycle key enzymes (succinate dehydrogenase (SDH) and malate dehydrogenation (MDH)), the level of intracellular reactive oxygen species (ROS) and nucleic acid content. The antioxidant activity was determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) methods. By gas chromatography-mass spectrometry (GC-MS) method, a total of 12 compounds were detected from the crude extract SE, of which the main component was 5-hydroxymethylfurfural (mass fraction 97.96%).   Biological test results showed that SE could inhibit the growth of R-67, and the IC₅₀ value was 0.46 mg/mL. SE could increase the conductivity and nucleic acid protein content of R-67, inhibit the specific activity of key enzymes in the tricarboxylic acid cycle SDH to MDH, increase the intracellular ROS content, and weaken the fluorescence intensity of (4′,6-diamidine-2-phenylindole) DAPI staining. Furthermore, it was preliminarily speculated that the mechanism of action included the inhibition of the cell membrane integrity of R-67, the damage of the cell structure, and the inhibition of the tricarboxylic acid cycle. The results demonstrated that the crude extraction of A. niger xj had a good application prospect in the biological control of A. konjac K. Koch during storage. And SE had a moderate ability to remove DPPH and ABTS free radicals, which was promising to be used in antioxidant functional products.