## 2 Materials and Methods
### Cell Culture  
HT29 cells were cultivated in DMEM supplemented with 10% FCS and 1% penicillin/streptomycin at 37 \({}^{\circ}\)C and 5% CO\({}_{2}\). Cells with passage numbers from five to twenty-five were used for cell culture experiments, to make sure that cells have adapted to culture conditions and receive a higher guarantee of comparability in the experiments. OPCs were dissolved in DMSO, which also served as a negative control (DMSO 1%) for the experiments. Each experiment was performed in three different cell passages, so that the results summarized three biological replicates.  
Assessment of the Antioxidant Potential Using a Modified Dichlorofluorescein Diacetate (DCFH2-DA) Assay  
The modified version of the DCFH\({}_{2}\)-DA assay was performed according to the protocol of [PERSON] et al. [24]. In a black 96-well cell culture microplate (Greiner Bio-One GmbH, Frickenhausen, Germany), 12,000 HT29 cells/well were seeded in 200 \(\mu\)L medium and cultivated for 72 h. Outer columns and rows were only filled with medium to ensure comparable conditions across the entire plate. Cells were washed with 200 \(\mu\)L/well PBS and pre-incubated with the test-substances in six different concentrations for 1 h under cell culture conditions. The medium was removed after 1 h and cells were washed with 200 \(\mu\)L/well PBS. From this point onwards, work was carried out in the absence of light. For the following incubation, 200 \(\mu\)L of 50 mM DCFH\({}_{2}\)-DA solution in PBS was added per well, and the cells were cultured under cell culture conditions for 30 min. The solution was removed, and the cells were washed with PBS as previously described. In the last incubation step, 200 \(\mu\)L/well serum- and supplement-free DMEM without phenol red were added to the cells of the negative control. All other cells were treated with 200 \(\mu\)L/well250 uM TBH solution in serum- and supplement-free DMEM without phenol red. Cells that had not been pre-incubated, yet had received TBH treatment, served as a positive control. The cell culture microplate was placed directly in a microplate reader (Infinite 200 pro, Tecan Austria GmbH, Grodig, Austria) which was pre-heated at 37 \({}^{\circ}\)C. The plate was shaken before every measurement, and the fluorescence intensity at \(\lambda_{\text{ex}}\) = 485 nm and \(\lambda_{\text{em}}\) = 535 nm was measured every 10 min for the total of 2 h. To determine the redox status of the cells of each well, the difference in the fluorescence between t\({}_{0}\) (starting fluorescence) and after 10 min, 30 min, 60 min, 90 min and 120 min was divided by the t\({}_{0}\). Thereafter, the calculated relative fluorescence intensity increase is related to the untreated negative control. In order to evaluate the antioxidant effects of the test-substances, a comparison was made with the positive control, which was exclusively incubated with TBH. Each experiment was implemented in biological triplicates with four technical repetitions. In order to obtain intrinsic fluorescence of the four tested analytes, a preliminary test was carried out. These were measured in the same concentrations and for the same lengths of time in medium without phenol red and afterwards corrected by means of a blank value (medium without phenol red). None of the four analytes exhibited intrinsic fluorescence.