The Dwarf Brazilian banana (Musa sp., group AAB) is grown and marketed widely in the Hawaiian islands, where it is known as the “apple” banana (Simmonds, 1954). These specialty bananas contain three times more vitamin C and 1.5 times more provitamin A than Cavendish-type bananas (Wall, 2006). Dwarf Brazilian bananas are limited in mainland U.S. and international markets because of quarantine restrictions. The fruit can be exported at the mature green stage under a nonhost quarantine status for Mediterranean [Ceratitis capitata (Wiedemann)], melon [Bactrocera cucurbitae (Coquillet)], and oriental fruit flies [Bactrocera dorsalis (Hendel)] (Armstrong, 1983, 2001). However, quarantine inspections for the presence of regulated insects [such as the green scale (Coccus viridis), coconut scale (Aspidiotus destructor), and banana moth (Opogona sacchari)] can delay or impede the shipment of bananas and lead to postharvest losses. The possible rejection of a shipment as a result of the presence of one or more insects poses a high financial risk for growers. The use of a quarantine treatment to control insects would reduce the need for inspections and improve market opportunities.
The island of Hawaii has a commercial electron beam facility that is used for quarantine treatment of tropical fruits. The facility offers a centralized location where growers can deliver fruit for quarantine treatment; therefore, small growers can participate in export markets. The USDA's Animal Plant Health Inspection Service (APHIS) issued a final rule to allow export of bananas from Hawaii after irradiation with a 400-Gy dose and inspection for the presence of banana moth, or after irradiation with a 150-Gy dose and inspection for banana moth and green scale (Federal Register, 2006). The 150-Gy dose provides quarantine security against coconut scale (Follett, 2006). The 400-Gy treatment is practical because inspections for banana moth are considerably easier than for green scale. However, banana fruit injury must be absent or minimal before the 400-Gy treatment can be used commercially. Local growers are interested in exporting irradiated bananas from Hawaii, but quality analyses are needed before markets can be developed and large shipments can be risked.
Most banana irradiation research has been done with Cavendish fruit (Musa spp., group AAA) with uncertain dosimetry. Phytotoxic symptoms generally occurred at target doses >500 Gy for preclimacteric fruit (Maxie et al., 1968; Thomas et al., 1971), but some authors report damage at doses as low as 400 Gy (Strydom and Whitehead, 1990). Irradiation injury appears as skin browning and has been attributed to an increase in polyphenol oxidase activity in the peel (Thomas and Nair, 1971). The maximum tolerable dose varied according to cultivar, physiological stage, storage conditions, degree of mechanical damage, and the time interval between harvest and irradiation treatment (Aina et al., 1999; Eric et al., 1970; Thomas et al., 1971). Bananas irradiated with doses up to 600 Gy tasted similar to control fruit (Strydom and Whitehead, 1990; Thomas et al., 1971). Higher doses (600 to 1000 Gy) may inhibit ethylene production and ripening (Strydom and Whitehead, 1990). During commercial treatment in Hawaii, the dose uniformity ratio for irradiated bananas is ≈1.5; therefore, some fruit may be exposed to >600 Gy when trying to achieve a minimum absorbed dose of 400 Gy. No information is available on the ripening behavior and quality of preclimacteric Dwarf Brazilian bananas after low doses (<1000 Gy) of irradiation. Also, the variability in maturity among hands within a bunch may impact banana radiotolerance and was not considered in previous studies.
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