Development of a PLC/IoT Control System with Real-Time Concentration Monitoring for the Osmotic Dehydration of Fruits

Osmotic dehydration (OD) is an effective pre-treatment for fruit preservation, but conventional processes often lack precision due to manual control of critical variables. This work reports the design and validation of an automated OD system integrating a programmable logic controller (PLC), human–machine interface (HMI), and IoT-enabled sensors for real-time monitoring of syrup concentration and process temperature. Mango (Mangifera indica) cubes were treated under a 2³ factorial design with sucrose concentrations of 45 and 50 °Brix, immersion times of 120 and 180 min, and temperatures of 30 and 40 °C. Validation demonstrated that the IoT hydrometer achieved strong agreement with reference devices (R² = 0.985, RMSE = 0.36 °Brix), while the PLC-integrated tank sensor also demonstrate improved performance over existing calibrated thermometer (R² = 0.992, MAE = 0.20 °C). ANOVA indicated that concentration, temperature, and time significantly affected water loss and weight reduction (p < 0.01), with temperature being the dominant factor. Water loss ranged from 18.62% to 39.15% and weight reduction from 9.48% to 34.47%, while maximum solid gain reached 9.31% at 50 °Brix and 40 °C for 180 min, with stabilization consistent with case hardening. Drying kinetics were best described by the Page model (R² > 0.97). The findings highlight the effectiveness of the system for precise monitoring and optimization of OD processes.