Development of a freeze-drying prototype with embedded technology to enhance value and extend the shelf life of asparagus for agricultural communities

Abstract

This study aims to develop and evaluate a freeze-dryer prototype to enhance the value and extend the shelf life of asparagus for agricultural communities. The research focuses on optimizing drying efficiency, energy consumption, and economic feasibility. The prototype was designed with a PLC-based control system featuring PID temperature regulation and real-time data transmission. The drying process was analyzed in terms of moisture reduction, drying rate, energy consumption, and operational stability. Experiments were conducted to assess performance across different production capacities. The freeze-dryer effectively reduces asparagus moisture content by 91.9 ± 0.3%, achieving a final moisture level of 8.1 ± 0.3%, which complies with dried food standards. The average drying rate is 0.00275 ± 0.00001 kg/hour. The system maintains an ice condenser temperature of -40 °C (±0.4 °C) and drying pressures between 0.90 and 0.95 mbar. Energy consumption analysis indicates that 51.9% of total energy is used during the primary drying stage. Increasing production capacity from 150 to 2000 grams significantly lowers energy consumption per unit, from 4,575 to 390 kWh/kg. Stability tests confirm continuous operation for 50 hours with an average power factor of 0.84 and voltage stability (%CV = 0.23). The developed prototype demonstrates high efficiency, operational stability, and cost-effectiveness. Economic analysis reveals economies of scale, with processing costs decreasing to 1,740 baht/kg at a 2000-gram capacity, though electricity remains a significant cost factor. This freeze-drying technology provides an effective solution for asparagus preservation, offering a viable approach for agricultural communities to enhance product value, reduce post-harvest losses, and improve economic returns.