Colour response of 'Cripps' Pink' apples to postharvest irradiation is influenced by maturity and temperature
Preliminary experiments indicated that postharvest irradiation enhanced anthocyanin synthesis in 'Cripps' Pink' apples. Consequently this system was used to understand the effects of maturity and temperature on anthocyanin synthesis. Fruits harvested 5, 4, 3, 2 and 1 weeks prior to predicted commercial harvest did not develop a red blush in response to postharvest irradiation (72h with high-pressure sodium lights at 20°C). Fruits harvested at maturity rapidly developed a red blush in response to irradiation. Mature 'Cripps' Pink' apples harvested from two growing regions were subjected to 120h of irradiation at 6 or 20°C following 0, 2 or 5 days at -0.5°C. Fruits harvested from the cooler area (Ceres) and irradiated immediately showed greater red colouration at 6°C than at 20°C. The difference between the temperatures was no longer significant after fruits have been stored for 5 days at -0.5°C prior to irradiation. Fruits harvested from the warmer area (Grabouw) were consistently redder when irradiated at 6°C than 20°C. In a separate experiment, fruits were stored for 20 days at -0.5°C prior to irradiation at either 6°C or 20/6°C (day/night). The alternating temperature resulted in better colour of fruits from both areas. In a final experiment, well-coloured 'Cripps' Pink' apples were irradiated at 37°C to simulate periods of high temperature that occur in summer. The hue angle of the fruits increased from 29.3 to 48.3° after 144h of light indicating a loss of red colour. The anthocyanin concentration decreased over 50% during the same period. Fruits kept at 37°C in the dark did not lose red colour. © 2001 Elsevier Science B.V.