Fig. 4. Total phenolic changes in untreated control (- C) and ethanol treated ( E) lettuce stem discs on day 1e6. (A) Total phenols in absorbance at 320 nm; (B) Total quinones in absorbance at 437 nm. Data presented are the means of six replicates. Different letters indicate significant differences among mean values (P < 0.05; t-test).