Nitric oxide inhibits cut-surface browning in four lettuce types

The ability of nitric oxide (NO) to inhibit the development of browning on the cut surfaces of four fresh-cut lettuce (Lactuca sativa L.) types (Green Oak, Green Coral, Baby Cos, and Butter) during storage at 5°C was examined. NO was applied to lettuce strips (i) by fumigation with NO gas for 2 h, (ii) by dipping in a solution of the NO-donor compound, 2,2³-(hydroxynitrosohydrazino)-bis-ethanamine (diethylene triamine-nitric oxide; DETANO) dissolved in 0.01 M phosphate buffer pH 6.5, or (iii) by dipping in an aqueous solution of the NO-donor compound, sodium nitroprusside (SNP).Treatment with NO gas, DETANO, or SNP inhibited the development of browning and extended the post-harvest life of all four lettuce types. The optimum treatments were dipping in 500 mg l^-1 DETANO or SNP, which resulted in an approx. 60% increase in post-harvest life over untreated lettuce slices. Fumigation with NO gas at 500 μl^-1resulted in a chemical-type injury, hence the optimum NO gas concentration was 100 μl^-1, which resulted in a 30% increase in post-harvest life. Dipping lettuce slices in 500 mgl^-1 SNP was considered to be the most feasible option for commercial processors due to the stability of SNP in unbuffered water, the universality of its effectiveness on a range of lettuce types, and the lack of any logistical difficulties in incorporating an additional water-dipping step into existing commercial line operations