Thermal insulation box design for maintaining cool temperature and the postharvest quality of okra

Abstract

Postharvest loss of okra is caused by its high respiration rate and temperature fluctuations in the supply chain. To address this, five thermal insulation boxes were designed, combining different materials, and evaluated for okra quality during simulated transportation and storage. The treatments included the standard foam box, metalized foam sheet (two layers consisting of aluminum foil and expanded polyethylene), prototype-A (three layers consisting of dual layer of aluminum foil and expanded polyethylene), prototype-B (four layers consisting of aluminum foil, nonwoven, expanded polyethylene, and aluminum foil), and standard regular slotted container. Material tests revealed that aluminum foil and expanded polyethylene had the lowest thermal heat energy. The composite sandwich box design, prototype-A, demonstrated the highest maximum insulation time of 28 h and thermal resistance of 0.332 m2°C/W. Prototype-A and prototype-B effectively maintained low temperature fluctuation, minimized air and okra temperature changes, and maintained 6.19 to 8.25 % CO2, which was within an acceptable range of 4–10 % for okra. Both prototypes exhibited reduced percentage mass loss in okra below 5 %. Importantly, both prototypes demonstrated the lowest incidence of okra pod surface browning and maintained the quality for 6 d, surpassing metalized foam sheet and standard regular slotted container. These findings offer sandwich design with 3 or 4 layers as promising alternatives for thermal insulation boxes in cold chain management, enhancing the transport packaging of okra under ambient environments compared to the standard foam box.