Effect of Heated Solutions on Decay Control and Residues of Imazalil in Lemons Mario Schirra,* ,† Paolo Cabras, ‡ Alberto Angioni, ‡ Guy D’hallewin, † Roberto Ruggiu, † and Elizabeth V. Minelli § CNR Istituto per la Fisiologia della Maturazione e della Conservazione del Frutto delle Specie Arboree Mediterranee, Localita ` Palloni, 09170 Oristano, Italy, Dipartimento di Tossicologia, Universita ` di Cagliari, viale Diaz 182, 09126 Cagliari, Italy, and Departamento de Quı ´mica Orga ˆ nica, Instituto de Quı ´micasUNESP, Araraquara, SP, Brazil Freshly harvested lemons [(Citrus limon (L.) Burm)] were dipped 3 min in water with and without imazalil (IMZ) at 50, 100, and 200 ppm at 50 °C and at 1000 ppm IMZ at 20 °C. Following treatments fruit were kept at 9 °C and 90%-95% relative humidity (RH) for 13 weeks and an additional week at 21 °C and ca. 75% RH, to simulate a marketing period (SMP). No decay control was observed with fruit dipped in water at 50 °C. In contrast, IMZ treatments provided 90%-96% control of Penicillium rots during cold storage and SMP. Fungi other than Penicillium spp. were also found in all samples as differences among treatments were negligible. IMZ treatment caused some external damage to the fruit (peel browning), and the percentage of damaged fruit was related to the amount of active ingredient (AI) present in it. Dipping in 200 or 1000 ppm IMZ promoted off-flavor development after 10 weeks of storage, and fruit were judged to be unacceptable for consumption after 13 weeks of cold storage. After 1000 ppm IMZ dipping at 20 °C, residue concentration in fruit was 8.20 ppm; this value doubled that found in a previous investigation on lemons treated with comparable IMZ levels. Residue concentrations in fruit after treatment at 50 °C was strictly related to the amount of fungicide employed. After 13 weeks AI residues in fruit decreased to average ca. 35% of the initial values. During the 1 week SMP, residue levels decreased by a further ca. 25%. It was concluded that it is possible to achieve significant control of decay in lemons during long- term storage by dipping fruit in 50 ppm IMZ mixtures at 50 °C. Such treatment should be advised to remarkably reduce potential pollution in the environment due to packinghouse wastewater disposal. Keywords: Citrus limon; postharvest; heat treatments; imazalil INTRODUCTION Over the last decade, the ever growing fear of risks coming from chemical residue contamination of horti- cultural crops and the public environmental concern on wastewater disposal after treatments have led to the implementation of studies and the improvement of postharvest technologies aimed at replacing or reducing the use of agrochemicals. Namely, postharvest heat treatments (high-temperature conditioning, hot water dipping) have been shown to reduce decay development, enhance fruit resistance to chilling injury, and greatly increase fungicide efficacy in various horticultural crops (Couey, 1989; Barkai-Golan and Phillips, 1991). The enhanced efficacy of fungicides against rots when applied in combination with hot water had been related to the effect exerted by heat in increasing coverage and penetration of the active ingredient (AI) into the fruit. It has been shown (Schirra et al., 1996) that dipping lemons in IMZ mixtures with concentrations ranging from 250 to 1000 ppm at 50 °C produced a 4.5-fold increase in fungicide residue levels in comparison with treatments performed at room temperature. A total control of decay was achieved by 1500 ppm IMZ treat- ment at room temperature, but when the fungicide was applied at 50 °C rot development was suppressed with 250 ppm of AI. Results reported herein provide additional informa- tion concerning IMZ potential to control storage decay in lemons, AI residue levels, and degradation patterns when very low rates of fungicide mixtures are applied at 50 °C in comparison to conventional treatments at room temperature. MATERIALS AND METHODS Plant Material. The experiment was carried out on Di Massa lemons [(Citrus limon (L.) Burm)] harvested at an advanced stage of maturity in the second week of June 1996 from a single lot of 12 trees growing in the National Research Council experimental orchard located at Oristano, Italy (cen- tral western Sardinia, 39° 55′ north latitude). Fruit Sampling. Fruits were delivered to the laboratory immediately after harvest, sorted to eliminate those with defects, selected for uniform size, placed in plastic boxes (48 boxes, 50 fruits per box), and grouped into eight treatment groups (six boxes per group, 2 boxes × 3 replicates), corre- sponding to the 3-min water dip treatments with and without imazalil (IMZ) at 50, 100, and 200 ppm IMZ at 50 °C and 1000 ppm IMZ at 20 °C and untreated fruit. IMZ mixtures in water were prepared with commercially available Fungazil 500 EC (44.66% AI, Janssen Pharmaceutica N.V. Belgium). Treatments and Storage Conditions. Fruit were dipped for 3 min in a bath fitted with 3.96 kW/h heating elements and an electronic recirculation pump (22 L/min water flow). Ambient temperature before treatment was 22 °C. Two hundred liters of water or fungicide mixtures were used for the treatments dipping one box of fruit per run. Bath temperature was constantly maintained within (0.5 °C of the required temperature by an electronic thermostat (OEM/HT, * Corresponding author. † CNR, Oristano, Italy. ‡ Universita ` di Cagliari, Italy. § UNESP, Brazil. 4127 J. Agric. Food Chem. 1997, 45, 4127-4130 S0021-8561(97)00207-0 CCC: $14.00 © 1997 American Chemical Society