Comparative Responses of Preharvest GA-treated Grapefruit to Vapor Heat and Hot Water Treatment

Abstract

`Marsh' grapefruit (Citrus paradisi Macf.) produced in Florida must be certified for security against unwanted pests before entry into some domestic and export markets. Application of heat by hot water (HW) has been shown to cause severe injury to grapefruit; however, direct comparisons between forced vapor heat (VH) and HW have been lacking. Grapefruit preharvest-treated with gibberellic acid (GA) or not treated, were postharvest-treated with VH or HW such that the surfaces of fruit were exposed to the same rate of temperature increases and treatment durations. Condition and quality attributes were then compared with ambient air (AA) and ambient water (AW) controls after storage. After 4 weeks' storage at 10 °C plus 1 week at 20 °C, scald affected 5% of HW and 20% of VH-treated fruit. No scald developed on control fruit. At the end of storage, mass loss for HW and VH fruit was ≈5%. HW-treated fruit had a 5-fold higher incidence of aging than VH fruit; however, control fruit showed significantly more aging than all heat-treated fruit. Gibberellic acid (GA) and the heat treatments reduced decay relative to the control. GA-treated fruit remained greener during storage than control fruit. These findings indicate that VH and HW treatments at the temperatures and durations to control the Caribbean fruit fly (Anastrepha suspensa, Loew) will likely cause peel injury to `Marsh' grapefruit produced in Florida, regardless of treatment with GA.