Effect of storage temperature and time on quality of Thompson seedless table grapes from Greece : A simulation of Reefer transport from South Africa or South America to the Netherlands: GreenCHAINge WP1 - Table Grapes

Abstract

The goal of this study is:1. to investigate the effects of optimal and sub-optimal transport temperature, i.e. -0.5 °C vs. 3.5 °C during two and three weeks, on the quality of Thompson seedless grapes from Greece.2. to investigate the effect of a decreased transport temperature, i.e. -1.5 °C, during two and three weeks on the quality of Thompson seedless grapes from Greece.Table grapes produced in South Africa and South America are transported in Reefer containers to the Netherlands. This will take two to three weeks’ time, depending on the route and the transport company.The temperature setpoint of these containers is usually -0.5 to 0.5 °C. At the start of the season in January, when Brix values are under 14°, the transport temperature will be set to be around 1.5 °C, to prevent low temperature decay.However, the temperature will only reach this setpoint close to the cooling unit, at de rear end of the container. Moving towards the door of the container, at the front end, temperatures will be higher and hot spots can occur when loading of the container is sub optimal. Temperature deviations of 2 to 3 °C from the setpoint have been reported, which will also affect product temperature.A better temperature distribution throughout de load, that approaches the set point temperature, could lead to a more homogeneous product temperature. To see whether this results in a better and more homogeneous product quality during the retail phase, grapes were stored at either -0.5 or 3.5 °C for both two and three weeks. Furthermore, since Thompson seedless table grapes have relatively high Brix values, the question arose whether grapes with such high levels of soluble sugars can be transported at a lower temperature, i.e. -1.5 °C, without showing quality issues.Our results show that on average, the quality of Thompson seedless table grapes from Greece is better when stored for two and three weeks at -1.5 and -0.5 °C than stored for those periods at 3.5 °C. However, within each temperature treatment the quality differences between replicates were large, involving punnets of moderate to bad quality in each treatment.On average, the quality of the grapes is better when stored for two weeks than for three weeks.The biological variation of the starting material appeared to be high, complicating outcomes of this postharvest study. It is currently unclear what exactly causes this variation in this case.The Brix values in week 38 to 42 were on average 19°. At start of the experiment, the question was whether grapes with relatively high levels of soluble sugars could be transported at a lower temperature, i.e. -1.5 °C, without showing quality issues. These grapes, with an average Brix value of 19° performed the same at -0.5°C as at -1.5°C, without showing more disorders at -1.5°C.