Application of Two Different MAP Systems in Order to Prolong the Shelf Life of Romaine Lettuce During Marine Shipment

Romaine lettuce has been reported to be one of the most sensitive products during marine shipping of fresh fruits and vegetables for supplying U.S. military bases in the Pacific region. We hypothesized that the quality loss observed at the specified 0.5 °C shipping temperature is likely due to dehydration of leaves or from cross-contamination by ethylene in mixed load containers. Two modified atmosphere packaging (MAP) systems were tested with Romaine lettuce: 1) Breatheway® Membrane Technology from Apio Inc. (California, USA) and 2) Xtend MAP from StePac L.A. Ltd (Israel). Romaine lettuce was obtained from South Bay, FL in waxed cartons. The product was transferred in an air-conditioned vehicle to the Postharvest Horticulture Laboratory of UF in Gainesville, FL and stored overnight at 0.5 °C. Lettuce was repacked into the two MAP systems and stored for 22 days at 0.5 °C plus 1 and 2 days at 20 °C. Romaine lettuce in the commercial packaging (without MAP) was the control. During the storage period, measurements of the atmospheres in the MAP systems were taken every other day. Neither of the two MAP systems proved to be beneficial for the products in delaying senescence. The Apio MAP system equilibrated at 14% O₂ plus 4% CO₂ during the storage at 0.5 °C and at 9% O₂ plus 4% CO₂ after two days of shelf life which resulted in CO₂ injury of the lettuce (brown stain). StePac bags equilibrated at an atmosphere of 19% O₂ plus 2% CO₂ during storage at 0.5 °C, which is not near to what is usually recommended as optimal for Romaine lettuce (i.e., a low O₂ atmosphere of 1-3%). When the lettuce was transferred to 20 °C, StePac bags established an atmosphere of 17% O₂ plus 4% CO₂, which resulted in CO₂ injury after 2 days at 20 °C but not after 1 day. Leaf wilting was a significant problem during 0.5 °C storage only for the control treatment and worsened after transfer of the control to 20 °C. We also tested the ethylene permeability of the two MAP systems at 20 °C and found the ethylene permeability rates to be extremely low. This suggests that cross-contamination by ethylene within mixed container loads of produce may not be a serious problem when the ethylene-sensitive products are in MAP.