INFLUENCE OF 1-MCP ON RUSSET SPOTTING IN LETTUCE MIDRIBS

Consumer demand for lightly-processed fruits and vegetables has consistently increased over the past few years. Of the fresh-cut industry, lightly processed lettuce is becoming a major fresh market product. However, midrib browning and russet spotting (RS) are problems that continue to challenge the product quality during storage and handling. Midrib browning results from the enzymatic and non-enzymatic oxidation of colorless phenolic compounds, which produce brown-colored pigment complexes, through a number of subsequent reactions. On the other hand, RS is a postharvest physiological disorder, induced in lettuce by exposure to ppm (µL L^-1.) levels of ethylene at ~5°C (Rood, 1956). RS is characterized by the appearance of numerous small brown spots along both sides of the midrib, which may spread over the leaf blade in severe cases. A number of treatments such as Ca, auxins and low-O₂ have been developed that reduce RS in lettuce. The suppression in RS due to low-O₂ has been related to the suppression of C₂H₄ action (Saltveit, 1999). The growth regulator, 1-MCP is a vapor under physiological conditions and acts by inhibiting the binding of the hormone C₂H₄ to its binding site, and a single exposure can temporarily render plant material insensitive to C₂H₄, when applied at the parts-per-billion level. In this investigation we evaluated the effect of 1-MCP on midrib browning and RS of lettuce stored at 5 and 20°C.