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Peter D. Petracek and D. Frank Kelsey

High-pressure washing (>689 to 3446 kPa or 100 to 500 psi at the spray nozzle) has been used recently in citrus packinghouses to improve the action of surfactant solution and brushing on the removal of dirt and superficial molds. Although high-pressure washing has no obvious detrimental effect on citrus fruit (e.g., no cellular breakage), its effects on physiology have not been fully examined. In this study gas samples were taken from the fruit core of `Orlando' tangelos, `Hamlin' oranges, and `Ruby Red' and white `Marsh' grapefruit prior to and following washing. An apparent wound ethylene response was measured for all varieties and was a function of prolonged exposure (>20 s) and excessive pressure (>2067 kPa). For the responding fruit, internal ethylene was initially detected about 3 h after washing, reached a maximum around 24 h (range: 0.1 to 0.6 ppm), and diminished to near background levels (0.0 ppm) after 48 h. No wound ethylene was observed when fruit were washed for the recommended exposure time (10 s) and pressure (1379 kPa). Concurrent decreases in internal O2 and increases in CO2 were observed for white and red grapefruit. High-pressure washing (1379 or 2757 kPa) did not affect water loss and water, O2, and CO2 exchange. The effects of subsequent waxing of the fruit (increased internal ethylene and CO2 levels and reduced of internal O2 levels) were amplified by washing at the higher pressure (2757 kPa).

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Peter D. Petracek, D. Frank Kelsey, and Craig Davis

The effect of high-pressure washing (HPW) on the surface morphology and physiology of citrus fruit was examined. Mature white (Citrus paradisi Macf. `Marsh') and red (Citrus paradisi Macf. `Ruby Red') grapefruit, oranges (Citrus sinensis L. `Hamlin'), and tangelos (Citrus reticulata Blanco × Citrus paradisi Macf. `Orlando') were washed on a roller brush bed and under a water spraying system for which water pressure was varied. Washing white grapefruit and oranges for 10 seconds under conventional low water pressure (345 kPa at cone nozzle) had little effect on peel wax fine structure. Washing fruit for 10 seconds under high water pressure (1380 or 2760 kPa at veejet nozzle) removed most epicuticular wax platelets from the surface as well as other surface debris such as sand grains. Despite the removal of epicuticular wax, HPW did not affect whole fruit mass loss or exchange of water, O2, or CO2 at the midsection of the fruit. Analysis of the effect of nozzle pressure (345, 1380, or 2760 kPa), period of exposure (10 or 60 seconds), and wax application on internal gas concentrations 18 hours after washing showed that increasing nozzle pressure increased internal CO2 concentrations while waxing increased internal ethylene and CO2 concentrations and decreased O2 concentrations. An apparent wound ethylene response was often elicited from fruit washed under high pressures (≥2070 kPa) or for long exposure times (≥30 seconds).

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Mark A. Ritenour, Teofilo Ng-Sanchez, and D. Frank Kelsey

Quaternary ammonia (QA) has been used on equipment and fruit bins in Florida to reduce the risk of spreading citrus canker. This study was initiated to understand the cause of a previously unknown peel injury believed to be associated with QA residues. Symptoms of QA injury on `Marsh' grapefruit (Citrus paradisi) usually developed within 24 to 36 h of contact with QA and ranged in severity from very slight discoloration to severe, dark brown, necrotic peel tissue that collapsed to form large sunken areas. Placing fruit in 10 mL (0.34 floz) of ≥100 mg·L-1 (ppm) fresh QA solution caused moderate to severe peel injury. Drying the QA solutions on polystyrene petri dishes and then redissolving the residue with 10 mL deionized water before fruit contact resulted in essentially the same degree of peel injury as contact with fresh QA solutions. Peel injury on early (November) or late-season (April) grapefruit also occurred when fruit were placed on a thin film of QA solution left on polystyrene petri dishes after dipping the dishes in ≥300 mg·L-1 QA solutions or if fruit themselves were dipped in QA solutions ≥500 mg·L-1. No significant peel injury occurred when dipping solutions contained only water with 200 mg·L-1 chlorine, 0.025% (v/v) Triton N-101, or a combination of both.