Postharvest storage of looseleaf lettuce (Lactuca sativa L.); the role of light, nutrients, bioactive levels and potential health benefits

Kerr CB and Burritt DJ

Department of Botany, University of Otago, 464 Great King St, North Dunedin, Dunedin 9016.

Up to one third of food grown for human consumption is lost or wasted. By improving post harvest storage techniques food waste may therefore be reduced. Once harvested, vegetables continue to sense and respond to environmental stimuli, the potential for photosynthesis is generally retained and secondary metabolites can still be produced. Leafy lettuce (Lactuca sativa) is a popular vegetable worldwide with many health promoting compounds, but it is also highly perishable. Lettuce is generally stored in the dark and this can potentially influence the levels of health promoting compounds present at the time of harvest. We are investigating whether storage of leafy lettuce cultivars in the light influences senescence, nutritional value and in particular the levels of health promoting compounds. Newly developed broad spectrum light emitting diodes (LED’s) that have a spectrum that more closely matches natural day light are being used. These have a low heat output, a long shelf life, low cost and are more environmentally friendly than traditional light sources. Two cultivars of leafy lettuce have been investigated so far. Data on bioactive metabolite levels, plant physiological responses, nutritional contents, and the ability if simulated human digests to protect human cells (Caco-2) from oxidative damage has been gathered. Storage duration and seasonal variations have also been investigated. It was found that lettuce digests stored under an appropriate lighting regime had a higher capacity to protect Caco-2 cells from hydrogen peroxide induced oxidative damage than digests from lettuce stored in the dark.