Peel injury on 'Marsh' grapefruit from Quaternary ammonia

Abstract

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 fl oz) 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.