Effect of various anti-browning agents on phenolic compounds profile of fresh lettuce (L. sativa)

High performance liquid chromatography (HPLC) was used to characterise phenolic profile and to select the most effective anti-browning compound(s) on fresh lettuce. Four anti-browning agents, ascorbic acid, cysteine, citric acid and oxalic acid were tested for their effectiveness on preventing loss of phenolic compounds in lettuce during processing and storage. Aliquots of the reaction mixture were withdrawn at different times varying from 0 to 24 h, and directly analysed by HPLC. Protocatechuic acid, chlorogenic acid, ferulic acid, caffeic acid, p-coumaric acid and phloridzin were identified in fresh lettuce. Degradation of phenolic compounds followed a first-order kinetic pattern. The effect of anti-browning agents on first-order degradation rates of phenolic compounds was determined. Lettuce treated with oxalic acid and ascorbic acid maintained a higher level of phenolic compounds than citric acid and cysteine. Interestingly, cysteine had no positive effect for the prevention of oxidation of phenolic compounds even though it prevented browning in lettuce.