Effect of increasing 4-coumaric acid concentrations on E. coli growth. E. coli was grown in modified M9 medium containing glycerol with increasing concentrations of 4-coumaric acid to determine growth inhibition. Concentrations of added 4-coumaric acid were as follows: (●) 0 mM, (■) 2 mM, (▲) 6 mM, (▼) 12 mM and (◆) 20 mM. Growth was determined by OD measurement at 600 nm. Cultures were supplemented with varying concentrations of 4-coumaric acid once the starter culture reached an OD of 0.1. Data points represent the means of three independent measurements.