Fig. 6. A variety of o-diphenol compounds can function with PPO to inhibit proteolysis. Control- (gray bars) or PPO-containing (black bars, 4.17 nkat mL^–1) alfalfa extracts (2 mg mL^–1 protein) were incubated with various o-diphenols (3 mM final concentration) and proteolysis, as amino acid release after 4 h, was measured. The tested o-diphenols were caffeic acid (CA), hydrocaffeic acid (HCA), chlorogenic acid (CGA), catechol (CAT), and (–)-epicatechin (EPI). Addition of ethanol (the solvent used for the o-diphenol stock solutions) served as a negative control (NONE). Results are the average ± SEM of three experiments using independently prepared extracts.