*3.10. Cell Viability*

Cell viability was assessed by the 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium (MTT) assay after 24, 48 and 72 h of exposure of the cells and seeded in 96-well plates to the different concentrations of red onion samples. After the incubation, 150 μL DMEM and 15 μL of MTT (5 mg/mL) were added to each well. The plates were incubated for 3 h at 37 ◦C. The media was removed, and formazan crystals were dissolved in 150 μL of isopropanol with gentle shaking. The absorbance was measured at 570 nm by the Victor 2030 multilabel reader (PerkinElmer, Waltham, MA, USA).
