2.3. Phenolic Extraction

Sorghum flour from each accession at 0.2–0.5 g was extracted in 10 mL of 70% aqueous acetone (v/v) for 2 h while shaking at low speed using a 211DS shaking incubator (Labnet International Inc., Edison, NJ 08817, USA) at room temperature, followed by storage at −20 °C in the dark overnight allowing the phenolics to be completely diffused from the cellular matrix into the solvent. The extract was then equilibrated at room temperature and centrifuged at 2970× g for 10 min. The residue was rinsed with an additional 10 mL of solvents with 5 min of shaking and centrifuged at 2970× g for another 10 min. Both supernatants were combined, and two aliquots were used for either total phenolic content determination or cell culture treatment. The aliquot for cell culture treatment was dried under a stream of nitrogen, and then dissolved in dimethyl sulfoxide (DMSO) to make a stock solution at −20 °C. Before its use for cell culture treatment, the stock solution was diluted with a fresh medium to achieve the desired concentration at 0–200 μM GAE. The final DMSO concentration in each treatment was kept at 0.1% v/v, which did not alter cell growth or cell cycle measurements significantly when compared with the DMSO-free medium. All extractions and treatments were conducted in triplicate.