1. What would be the ideal control for these assays like DPPH and ABTS?

while go through various literature, i noticed some authors use growth medium (MRS broth) as a control, others use water as a blank, and some even use the water as a control. This has left me a bit uncertain because i tried using both water and MRS broth, and my results varied significantly, with the percentage ranging from low to high depending on the control choice.

I'd be grateful for your suggestions.

Thank you in advance!