Optimum cooling and transport temperatures for plums from areas situated far from cooling facilities/depots

Temperature profiles of uncooled plums and force-air cooled (FAC) plums on site (at the farm) and transported in refrigerated trucks, from Ladismith to Paarl were recorded in two separate consignments. These temperature profiles were simulated under laboratory conditions and a field-heat removal (FHR) treatment was added. The objective was to obtain typical temperature profiles for different cooling and transport methods and to quantify the effect of these temperature profiles, as well as FHR on plum quality.

The temperature profile of uncooled plums transported in refrigerated trucks, to the cooling/ loading facilities (Paarl area), as well as FAC plums in the production area (Ladismith) were determined by data collection with loggers, from packing until the end of forced-air cooling. Fruit pulp and air temperature were recorded in three commercial pallets during each transport leg. These temperature profiles were simulated under laboratory conditions and a field heat removal (FHR) treatment was added, to ascertain the effect on plum quality

Pulp temperatures of uncooled plums, in standard 5 kg boxes, loaded at 24.4 °C to 17.9 °C were not reduced during transport at 2 °C. The exception was plums packed in punnets, where pulp temperatures were reduced by 5.5 °C. In FAC plums, pulp temperatures were maintained. In 2016, flesh firmness and shrivel was similar in FAC and FHR plums. Uncooled plums were significantly softer and more shrivel occurred. In 2017 the trend was similar.

Fruit quality data suggest that FAC on site, as well as field heat removal to 10 °C, may be beneficial in terms of flesh firmness retention, moisture loss and shrivel control, compared to uncooled plums transported in refrigerated trucks. In some instances these results were significant.