Light and temperature affect postharvest colour development in 'Cripps' Pink' apples

Since postharvest irradiation can enhance blush development in apples this system was used to understand the interactions between light and temperature on anthocyanin synthesis. 'Cripps' Pink' apples harvested from two growing regions, Grabouw and Ceres, were subjected to 120 h of irradiation at 6 degreesC or 20 degreesC following 0, 2 or 5 days at -0.5 degreesC. Fruit harvested from Grabouw were consistently redder when irradiated at 6 degreesC than 20 degreesC, although there was slight improvement in colour after storage at -0.5 degreesC for 5 days prior to irradiation. Fruit harvested from Ceres and irradiated immediately showed increased anthocyanin synthesis at 6 degreesC compared to 20 degreesC. The difference between the temperatures was no longer significant after fruit had been stored for 5 days prior to irradiation. In a second experiment, fruit were stored for 20 days at -0.5 degreesC prior to irradiation at either 6 degreesC or 20 degrees /6 degreesC (day/night). The fluctuating temperature resulted in better colour and higher anthocyanin concentrations for fruit from both areas. The hue angle of well-coloured 'Cripps' Pink' apples irradiated at 37 degreesC increased from 29 degrees to 48 degrees and the anthocyanin concentration decreased from 740 ug(.)g(-1) to 284 ug(.)g(-1) after 144 h of irradiation. Fruit held at 37 degreesC in the dark did not show any loss of red colour or anthocyanin degradation.