A COMPARATIVE STUDY OF THREE DRYING TECHNIQUES FOR APPLE POMACE VALORIZATION BASED ON KEY PERFORMANCE INDICATORS

Abstract

This study presents a comprehensive evaluation of three drying techniques (freeze drying, hot air drying, and electrohydrodynamic drying) for the valorization of apple pomace. The drying kinetics of each method were experimentally investigated, followed by an assessment of key performance indicators, including energy efficiency, environmental impact, economic feasibility using scaled-up 50-kilogram capacity dryers, and product quality attributes such as phenolic content, color, texture, and microbial stability. Electrohydrodynamic drying demonstrated superior energy performance, with the lowest specific energy consumption (0.34 kilowatt-hour per kilogram of water removed) and minimal carbon footprint (0.16 kilograms of carbon dioxide equivalent per kilogram of water removed). Freeze drying outperformed the other methods in quality-related parameters, including the highest phenolic content, and superior color and texture scores. However, it incurred higher energy costs and carbon emissions. Hot air drying showed the least favorable performance across most indicators, particularly in energy use and product quality. A multi-criteria decision analysis using a weighted sum model was employed to integrate all key performance indicators, resulting in FD ranking highest (aggregated score: 0.68), followed by EHD (0.65), and HAD (0.22). Additionally, an economic analysis revealed that EHD achieved the lowest annualized drying cost (approximately $32,415/year), reinforcing its economic competitiveness. These findings support EHD drying as a promising low-temperature and scalable alternative for sustainable apple pomace valorization, particularly where energy efficiency and cost-effectiveness are prioritized, while FD remains the preferred method when product quality is the primary goal.