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Abstract
This study investigated the application of low-cost smartphone-based infrared (SBIR) cameras and computer simulations (CS) to improve the precooling operations of lettuce and cantaloupe. The performance of several SBIR cameras (FLIR and Seek) and two handheld thermal cameras was compared against traditional temperature acquisition devices under simulated conditions of harvesting, packing, hydrocooling, and cold storage. The FLIR SBIR cameras demonstrated superior efficacy in capturing thermal images of the fresh produce across all evaluated conditions compared to the Seek SBIR cameras. Thermal images facilitated quicker decision-making for correcting process deviations compared to conventional temperature measurements. Then, a laboratory vacuum cooling (VC) system was designed and compared with simulated immersion hydrocooling (IH) to evaluate their cooling performance on iceberg lettuces and cantaloupes. Both precooling methods effectively reduced the temperature of iceberg lettuces, with VC providing a greater cooling homogeneity than IH. Next, a three-dimensional (3D) computational fluid dynamics (CFD) model based on finite volume method was developed to study heat transfer phenomena during the VC of iceberg lettuce. The predicted CFD outcomes were validated against experimental results, demonstrating strong agreement with R2 = 0.9988 and RMSE = 0.44 ℃ for surface temperature R2 = 0.9915, and RMSE =1.46 ℃ for internal temperature. Then, a further investigation assessed the effect of VC and storage arrangements (two or three shelving units) within the walk-in cooler on quality attributes of lettuce during cold storage. Vacuum-cooled lettuces showed better quality than non-vacuum-cooled lettuces by reducing moisture loss, delaying yellowing, slowing the degradation of chlorophyll and ascorbic acid, and preserving phenolic content and antioxidant activities during twelve days of refrigerated storage. The addition of one extra shelving unit did not compromise lettuce quality. CFD models of storage arrangements during cold storage of lettuces were developed to investigate the airflow and temperature distribution inside the walk-in cooler over 24 h. The developed CFD models were accurate for predicting temperature evolution with R2 value ranged from 0.9571 to 0.9787, and RMSE value ranged from 0.4978 ℃ to 0.7861 ℃. The study demonstrated that current precooling of fresh produce can be effectively studied and optimized using SBIR cameras and CS.