Identifying cooling heterogeneity during precooling and refrigerated trailer transport for the citrus supply chain by extensive temperature monitoring within full-scale experiments

To prevent postharvest losses, optimal fruit temperatures should be maintained. However, non-uniform hygrothermal conditions and hotspots can develop due to the dense stacking of the fruit inside refrigerated trailers. The question remains when and where they arise. In commercial shipments, only the air temperature at the back of the trailer is typically monitored. However, it is still unknown how this temperature relates to fruit temperatures within the cargo. This study experimentally measured air and fruit temperatures for citrus fruit transported from Greece to Switzerland within a commercial supply chain. 108 sensors were placed inside one shipment to map air and fruit temperature gradients and identify hotspots during precooling and transport. Besides, air and fruit temperatures were measured at the back of the trailer within 30 additional shipments to analyze the variations between different transports. The results showed insufficient precooling (room precooling), as not all fruit reached the required setpoint temperature (4-6 °C) after 24 h of precooling. Although most of the field heat was removed during precooling, re-heating (>10 °C) of some fruit in the middle of the trailer was observed due to insufficient ventilation of the pallets. Finally, different shipments showed varying air temperatures (average interquartile range: 1.5 °C), where significant variations were observed between different shipments (up to 9 °C difference between the average temperatures) and where the measured air temperatures deviated from the setpoint. The results of this full-scale experiment indicate the importance of monitoring commercial supply chains to better understand transport processes within refrigerated trailers and prevent fruit losses.