S23 - Session P1 - Improving 'Honeycrisp' red skin coloration using postharvest ultraviolet irradiation treatments under different storage temperatures

Authors: Yixin Cai, Rohan Tikekar, Joseph Sullivan, Macarena Farcuh *

Poor red skin coloration at harvest is a major factor limiting production and marketability of the profitable apple cultivar 'Honeycrisp'. Light wavelength and intensity together with temperature affect red skin coloration during ripening on-the-tree and throughout storage. Our goal was to evaluate and compare the effect of different postharvest ultraviolet (UV) irradiation treatments, applied under different storage temperatures on 'Honeycrisp' skin red coloration, surface blush percentage, and ethylene production rate. 'Honeycrisp' fruit were harvested at optimal maturity, and submitted to postharvest UVA (600,800,1200,2400 kJ m -2 ) and UVB (200, 400, 600, 800 kJ m -2 ) irradiation treatments on the unblushed side during a seven-day conditioning period at either 5 ºC or 10 ºC, and transferred to cold storage at 3 ºC, along with dark and white light controls. Evaluations were conducted at the end of the conditioning period and biweekly during 3 ºC storage for up to eight weeks. Our results showed a dose-dependent, dramatic decrease in hue values of the skin, with 2400 kJ m -2 UVA and 800 kJ m -2 UVB displaying the lowest hue values. The dose dependent increase in red skin coloration observed for UVA and UVB correlated with a significantly higher skin red blush percentage area. These red skin coloration differences were higher in fruit treated at 10 ºC compared to those treated at 5 ºC. No differences were observed in ethylene production rates in fruit submitted to UV treatments, regardless of the wavelength, dose, or conditioning temperature, compared to control fruit. Overall, postharvest UV irradiation is a promising tool for promoting postharvest skin coloration in 'Honeycrisp' apples. Our results contribute to the identification of optimal dosage application treatments.