Effects of Heat-Tunnel Temperatures on the Quality of Shrink-Film-Wrapped Lettuce

Excerpts from the report: Prepackaging of lettuce in heat-shrinkable films at shipping points has recently created considerable interest among lettuce shippers and marketing agencies. To date, only a small number of shippers are marketing prepackaged lettuce, almost all of it in heat-shrinkable film. Some shippers are skeptical of this practice. Others are reluctant to invest in the packaging machinery and equipment required for a large-volume operation. In recent months, shrink-film-wrapped lettuce with discoloration of leaf margins, that resembled tipburn, has been observed occasionally in New York City retail stores. Federal and private produce inspectors have found similar leaf damage in a few New York deliveries of prepackaged lettuce during the past year. Wilting and discoloration of the outer leaves in shrink-film-wrapped lettuce have been reported in a survey of several terminal markets. The possibility of heat damage was mentioned in that report, but it was apparently discounted. Because high temperatures are required to shrink the film overwrap now used commercially, tests were conducted to determine if heat-tunnel temperatures affected lettuce quality. The study on which this report is based was undertaken as part of the Agricultural Marketing Service's research program to maintain the quality of farm products in marketing channels.