Effect of some pre- and postharvest treatments on browning inhibition in fresh cut lettuce during cold storage

Abstract

An experiment was carried out at the Agricultural Experiments and Researches Station, Faculty of Agriculture, Cairo University during the winter season of 2008/2009 and 2009/2010 seasons, to study the influence of foliar spray of citric acid at 1.0 and 2.0 g/L (0.1 and 0.2%), in addition to potassium sulfate at 2.5 g/L (0.25%) [pre-harvest treatment] and evaluate the effect of dipping the lettuce cut stem of all the previous field experiment with dipping in citric acid at 5 g/ 0.1 L (5%) or coated by sugar syrup at 100% (post harvest treatment) and determine those which the prevention of butt discoloration (browning of the cut stem lettuce) and maintained quality during storage at 0°C and 95 % relative humidity (RH) for 12 days. Results indicated that spraying the lettuce plants with 2 g/L of citric acid + 2.5 gm/L of potassium sulfate reduced the weight loss percentage, total phenolic contents and inhibited polyphenol oxidase (PPO) activity and gave good appearance in their heads when compared with the control. Treating cut stem lettuce with citric acid at 5% or sugar syrup as postharvest treatments is the most effective for controlling the enzymatic of browning reaction and protected phenolic compounds from oxidation during storage. The best and beneficial results were obtained when spraying lettuce plants in the field with 2 g/L citric acid + 2.5 g/L potassium sulfate, in addition to, dipping their cut stem lettuce in sugar syrup 100% solution before storage. This completely inhibited browning on lettuce stem cutting (indicating by lower chroma value and higher hue angle), maintained quality and gave lettuce heads with good appearance for 12 days at 0°C and 95% RH.