To confirm browning did indeed result from a time-dependent reaction and was not solely due to catechol's intrinsic colour, spectral scans were performed at t = 0 (immediately after addition of catechol to DMEM) and after 96 h of incubation at 37 °C (Fig. ). After 96 h of incubation with 15.6 mM catechol, the solution darkened visibly, with pronounced shifts in the UV-visible spectrum of DMEM (300-500 nm), requiring sample dilution to one-third of original concentration to remain within the instrument's quantifiable range.