Nitric oxide prevents wound-induced browning and delays senescence through inhibition of hydrogen peroxide accumulation in fresh-cut lettuce

• Published in: Innovative food science & emerging technologies 2015-08, Vol.30, p.157-169
• Main Authors: Iakimova, Elena T., Woltering, Ernst J.
• Format: Article
• Language: English
• Subjects: ammonia-lyase activity; Browning; Cell death; disease resistance response; Fresh-cut lettuce; Hydrogen peroxide; iceberg lettuce; lactuca-sativa l; Nitric oxide; phenolic metabolism; postharvest senescence; processed romaine lettuce; programmed cell-death; shelf-life; short-term exposure; Wounding
• ISSN: 1466-8564; 1878-5522
• DOI: 10.1016/j.ifset.2015.06.001

As a source of bioactive ingredients, lettuce is a preferable component of a healthy diet. In recent years the production of fresh-cut produce has become a fast growing business. However, the shreds are highly sensitive to wound-induced browning and premature senescence that substantially reduces the visual and sensory qualities and shortens the shelf life. To improve the fresh-cut quality, in this work, short pre-storage exposure of shreds from butterhead and iceberg lettuce to nitric oxide (NO) gas was applied. It was found that fumigation with 100 and 200ppm NO for 1 or 2h remarkably inhibited the browning of the cut surface and of other injured leaf areas; NO treatment delayed the senescence and substantially prolonged the shelf life upon storage at 4°C and 12°C. To obtain information on the physiological processes involved in the wound response, the generation of hydrogen peroxide (H2O2) and the occurrence of cell death were analyzed. The results revealed that the wounding stimulated the accumulation of H2O2 thus generating oxidative stress leading to cell death. A correlation between elevated H2O2 levels, cut surface browning, senescence and storability of the fresh-cuts was established. In comparison to mature leaves, younger leaves expressed a lesser susceptibility to wound-induced browning and the associated oxidative stress. Applied NO strongly inhibited the H2O2 accumulation which may explain its beneficial effects. We demonstrate that short treatments with NO gas substantially inhibit wound-induced browning and largely improve the storability of fresh-cut lettuce. This offers an option for adopting NO treatments for optimization of the post-processing conditions. Implementation of reported findings into practice will offer innovative technological solutions for improvement of the post-harvest quality of fresh-cut lettuce applicable for the industry, distributors and retailers. Moreover, our findings indicate that the browning disorder is to a large extent dependent on the severity of the wound-induced oxidative stress and cell death occurrence. This discovery opens a possibility for the development of metabolic and morphological markers appropriate for the prediction of the quality and shelf life of fresh-cut lettuce with perspective for expanding the research and introducing the tests toward other perishable leafy vegetables. •The wound response of fresh-cut lettuce involves H2O2 generation and cell death.•Browning of wounded leaf tissue is as