The United States produced 407,000 t of ‘Bartlett’ pears (Pyrus communis L.) in 2012 [U.S. Department of Agriculture (USDA), 2013]. California produces ≈32% of all pears in the nation and exports between 20% and 30% of the fresh crop each year to Canada, Mexico, Costa Rica, Honduras, Guatemala, Brazil, and eastern Russia (California Pear Advisory Board, Pear Pest Management Research Fund, California Specialty Crops Council, University of California Cooperative Extension, 2011; California Foundation for Agriculture in the Classroom, 2011).
A consequence of globalized trade is the risk of introducing or spreading insect pests; therefore, phytosanitary measures are required to disinfest fresh produce leaving a quarantine area (Hallman, 2011). Common pests that affect pears include the codling moth (Cydia pmonella), pear psylla (Cacopsylla pyricola), eriophyid mites (Acarina: Eriophyidae), and oriental fruit moth (Grapholita molesta) (California Pear Advisory Board, Pear Pest Management Research Fund, California Specialty Crops Council, University of California Cooperative Extension, 2011).
Methyl bromide (MB) is a common fumigant for quarantine treatment in the United States (Drake et al., 2003; Environmental Protection Agency, 2014; Methyl Bromide Technical Options Committee, 2011). However, MB has been identified as a controlled ozone-depleting chemical by the Montreal Protocol since 1992. Although the use of postharvest fumigation is not scheduled for a phaseout, the use of MB will continue to decrease; thus, alternative phytosanitary measures to MB are needed.
Ionizing irradiation disrupts the deoxyribonucleic acid , which leads to the inability of the cell to replicate and cell death. Insects are highly vulnerable to irradiation and a dose of 0.05 to 0.15 kiloGray (kGy) is sufficient to sterilize most insects of concern (Miller, 2005). The USDA-APHIS has set an irradiation phytosanitary dose target of 0.15 kGy for the tephritid fruit fly and 0.4 kGy for other insects that do not include the pupa and adult stages of Lepidoptera [USDA–Animal and Plant Health Inspection Service–Plant Protection and Quarantine (USDA APHIS PPQ), 2013]. The U.S. Food and Drug Administration (FDA) allows a maximum of 1.0-kGy irradiation dose on fresh produce (FDA, 2011); thus, 0.40 to 1.0 kGy is within the permissible dose range for fresh fruit.
Previous studies indicate that irradiation affects the enzymes involved in ripening of pears (Maxie et al., 1966; Wani et al., 2008). ‘Anjou’ and ‘Bosc’ pears ripened at a slower rate after irradiation exposure and allowed for one additional day of shelf life (Drake et al., 1999). Abolhassani et al. (2013) also reported that ‘Bartlett’ pears experienced a delay in ripening of 1 to 2 d when subjected to a minimum dose of 0.4 kGy.
Pears are susceptible to postharvest bruising and become more vulnerable after the mature-green stage when the fruit begin to soften during ripening (Abolhassani et al., 2013; Mitcham et al., 1996). An additional step in the supply chain such as irradiation and the associated handling could potentially elicit a wound response or increase the susceptibility to bruising. The target dose for phytosanitary treatment is 0.4 kGy; however, during commercial treatment, some portions of the fruit can be exposed to dose levels twice as high, depending on the size of the cartons, density of the fruit, packing density, and irradiation modality. Abolhassani et al. (2013) observed increased bruising in early-harvest pears irradiated at a minimum dose of 0.80 kGy. Signs of bruising are manifested as the fruit ripens and handling as would occur in a grocery situation can exacerbate bruising symptoms. The objective of this study was to determine the effect of phytosanitary irradiation on the ripening quality of California-grown ‘Bartlett’ pears under simulated commercial conditions of treatment and retail display where they would be exposed to handling typical in grocery stores. After exposure to irradiation treatment, the pears were evaluated daily during ripening for changes in respiration rate, ethylene production, and quality attributes followed by sensory testing at peak ripeness.
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