Modified Atmospheric Drying of Fruits and Vegetables: Equipment, Kinetics, and Feasibility

Abstract

Fruits and vegetables, with high moisture levels of 85%–95% and 75%–96%, respectively, are susceptible to enzymatic activity and external factors, leading to rapid degradation through oxidative reactions, microbial proliferation, and respiration mechanisms such as ethylene emission. Drying, a critical preservation method, relies on heat and mass transfer driven by temperature and vapor pressure gradients. However, excessive thermal exposure and oxygen interaction often deteriorate bioactive compounds. Removing oxygen during drying offers a promising strategy to mitigate degradation and enhance product stability. Modified atmospheric drying (MAD) is an advanced technique that replaces atmospheric oxygen with alternative gases such as CO₂, N₂, or H₂ to improve drying efficiency and product quality. This review represents the first comprehensive effort to systematically consolidate recent developments in MAD, providing insights into operational mechanisms, equipment design, drying kinetics, quality preservation, and industrial feasibility, with emphasis on potential to reduce oxidation, retain nutrients, and preserve structural integrity. Compared to traditional drying, MAD achieves up to 18% improvement in effective moisture diffusivity, a 17%–29% reduction in drying time, and up to 6% increase in rehydration potential. It also enhances retention of nutritional and bioactive compounds, with total phenolic content maintained at 15%–25% higher levels, ascorbic acid degradation reduced by up to 15%, and improved color stability reflected in a decrease in total color difference (ΔE) of up to 11%. CO₂ inhibits enzymes in aqueous and fatty matrices, whereas N₂ reduces oxidative and microbial deterioration. Overall, MAD improves product quality, shelf life, and energy efficiency, lowering production costs.