Nitric oxide inhibits cut-surface browning in four lettuce types

Abstract

SummaryThe 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 5ºC 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, 2,2’-(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 l–1 resulted in a chemical-type injury, hence the optimum NO gas concentration was 100 µl l–1, which resulted in a 30% increase in post-harvest life. Dipping lettuce slices in 500 mg l–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.