Submitted to: HortScience
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/4/2012
Publication Date: 8/1/2012
Citation: Fan, X., Sokorai, K.J., Niemira, B.A., Mills, R.S., Zhen, M.Y. 2012. Quality of gamma ray-irradiated iceberg lettuce and treatments to minimize irradiation-induced disorders. HortScience. 47:1108-1112. Interpretive Summary: Ionizing irradiation is allowed to be used on Iceberg lettuce to enhance microbial safety. However, information is needed regarding quality changes of whole head lettuce after irradiation. This study was conducted to investigate effects of irradiation on the quality of head Iceberg lettuce and explore means to reduce irradiation-induced injury. Results showed that irradiation induced discolorations of lettuce and low oxygen packaging eliminated the injury caused by irradiation. The results may be used by the produce industry to employ the technology to minimize the risk of foodborne diseases.
Technical Abstract: Irradiation of Iceberg lettuce was recently approved by the FDA to enhance microbial safety and to extend shelf-life at doses up to 4 kGy. However, the radiation tolerance of whole head lettuce is unclear. The present study was conducted to investigate the effects of irradiation on the quality of head Iceberg lettuce and explore means to reduce irradiation-induced injury. In the first experiment, head lettuce was irradiated at 0, 0.5 and 1.0 kGy and stored at 4 C for 14 days. In subsequent experiments, the following treatments were used to reduce irradiation-induced injury: pretreatment with 1-methylcyclopropene (1 MCP) before irradiation, modified atmosphere packaging during and after irradiation, and oxygen exclusion during irradiation. Irradiation-induced symptoms similar to russet spotting and other discolorations (pink ribs, rusty brown and vein brown) both in external leaves and internal leaves were observed on day 7 and 14 after irradiatio at 4C. Irradiation at 0.5 and 1.0 kGy had no consistent effect on butt discoloration, decay or softening of lettuce. Pretreatment with 1-MCP and irradiation in the absence of oxygen had little effect on the irradiation-induced tissue discoloration. However, modified atmosphere packaging almost eliminated the injury caused by irradiation. Our results suggest that modified atmosphere packaging could be used to negate irradiation-induced injury in head lettuce.