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Antioxidant and antiaflatoxigenic activity of quercetin

Antioxidant and antiaflatoxigenic effects of quercetin (QC) were investigated using Aspergillus flavus NRRL 3251 grown on glucose minimum salts (GMS) microbiological medium. This naturally occurring flavonoid induces oxidative stress in cells which in turn respond by increased synthesis of protective proteins resulting in overall antioxidant effects in the cell. Oxidative stress is one of the prerequisites for aflatoxin biosynthesis, so antioxidants like QC should inhibit aflatoxin production. To test its antiaflatoxigenic activity, QC quantities spanning four orders of magnitude were added to GMS medium: 10, 1, 0.1 and 0.01 ppm. Inoculated media were incubated for 48, 96 and 144 hours, and the grown mycelia were filtered and weighed. Aflatoxins (B1, B2, G1, and G2) were determined in the medium using immunoaffinity cleanup followed by LC-MS/MS analysis. Mycelium was disrupted using ultrasonic probe and activity of selected antioxidant enzymes was determined (catalase (CAT), glutation reductase (GR), glutation S-transferase (GST)) in supernatants while reactive oxygen species (ROS) were determined in undisrupted mycelia. QC showed strong antiaflatoxigenic effect during the incubation period reducing total aflatoxin levels from 362.14 ppb to 0.24 ppb at the 0.1 ppm QC concentration. The added QC also increased ROS levels compared to control, as well as GST, GR, and CAT activity. Induction of the enzymes was an expected result in the context of enhanced cellular oxidative stress. Presumably, the enzymes successfully contained the ROS levels thereby reducing aflatoxin production by the fungus.

Aspergillus flavus; quercetin; reactive oxygen species; antioxidant enzymes; antiaflatoxigenic effect

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