| Summary: | 碩士 === 國立臺灣大學 === 園藝暨景觀學系 === 105 === Iceberg lettuce (Lactuca sativa L. var. capitata；Crisphead lettuce) belongs to the Asterraceae, is most yield and consumption for vegetable in the world. Harvesting lettuce causes wounding at the stem end which turned from white to reddish-brown. This phenomenon was called butt discoloration and was considered a defect in quality attributes of head lettuce. It was well known that wounding of plant tissues usually induces the activity of phenylalanine ammonia lyase (PAL) and results in the accumulation of phenolic compounds, which were then oxidized to quinones by polyphenol oxidase (PPO) and eventually condensed spontaneously to brown pigments. Several researches had indicated that acetic acid treatment or modified atmosphere packaging can prevent cut surface of lettuce from browning. The objective of this study was to use the edible vinegar instead acetic acid and investigate the influence of different treatment, packaging specification, packaging material and packaging treatment on surface browning and quality of wounded stem of head lettuce. Soaking lettuce stem discs in 2% and 3% acetic acid stored at 5℃ inhibiting of a* value , PAL activity and total phenolic content. 1.5% apple vinegar treatment compared to the same concentration of Kong yen rice vinegar, rice vinegar and premium rice vinegar were more effectively of inhibiting a* value. Using sponge soak in apple vinegar and moistening on the surface of lettuce stem for 5 seconds, a* value and b* value were been inhibited. This result is the same as soaking which used before, so we can substitute sponge moistening for soaking. The results of the cut lettuce stem replace stem discs show that the concentration of browning increased with the increase of the volume of the sample. The apple vinegar treatment with packaging can inhibit a*, b* value, reduce the degree of browning and maintain the quality of lettuce. The more sealing of package specifications the more inhibition of a * value and the degree of browning rise, presumably due to the reduction of oxygen concentration in the bag and carbon dioxide accumulation. Polyethylene material with apple vinegar solution can significantly inhibit the degree of browning, and low-density polyethylene material has better results. The apple vinegar using in surface of lettuce stem with passive modified atmosphere packaging using deoxidizer, active modified atmosphere packaging with 5% O2 and 0% CO2 and vacuum packaging, each treatment did not have obvious difference in a*, b* value, browning score. The carbon dioxide concentration did not reach the standard of injuring the leaf ball of lettuce, it maintain below 1%. This result suggested that using LDPE packaging film with the treatment of apple vinegar could effectively solve the problem of harvesting lettuce causes wounding at the stem end which turned from white to reddish-brown.
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