What question did this study set out to answer?

To evaluate the effects of different drying methods and pretreatments on onion quality and drying efficiency.

February 2, 2026

Drying of Onion and Onion Slices: Comparative Methods and Their Impact on Kinetics, Quality, Nutritional Properties, Modelling, Drying Efficiency, and Energy Consumption: A Review

Key Points

To evaluate the effects of different drying methods and pretreatments on onion quality and drying efficiency.
Reviewed various pretreatments including brining, blanching, and ultrasound.
Compared conventional drying methods (sun, hot-air) with advanced techniques (vacuum, freeze drying).
Analyzed energy consumption and cost economics for each technique.
Utilized mathematical models like thin-layer (Page, Logarithmic) for predicting drying behavior.
Blanching and ultrasound improved drying efficiency and quality.
Conventional methods often led to nutrient loss and color changes.
Hybrid drying systems achieved better product quality with reduced energy use.
Lower temperatures preserved phenolics and vitamin C more effectively.

Abstract

ABSTRACT Onion drying is an essential post‐harvest process that extends shelf life and preserves the nutritional, functional, and sensory qualities of onions. This review evaluates the influence of various pretreatments (brining, thermal, non‐thermal, and potassium metabisulfite) and drying methods (open sun, solar, convective, microwave, and freeze drying) on drying kinetics, quality characteristics, energy efficiency, and cost economics. Among pretreatments, blanching and ultrasound notably improved drying efficiency by enhancing moisture diffusion, reducing drying time, and maintaining product quality. Conventional drying methods, such as sun and hot‐air drying, are simple and low‐cost but often lead to nutrient degradation, color changes, and reduced sensory appeal. In contrast, advanced and hybrid drying technologies (vacuum, freeze, and low‐pressure superheated steam drying) ensure better retention of bioactive compounds, thiosulphinates, and aroma while improving rehydration capacity. However, these techniques are often limited by high energy requirements and scalability issues. Hybrid drying systems provide the most effective compromise between product quality and energy efficiency, achieving higher moisture removal with reduced specific energy consumption. Mathematical models, particularly thin‐layer (Page, Logarithmic) are used for predicting drying behavior and optimizing parameters. High‐temperature drying can cause color darkening and volatile losses, whereas low‐temperature or vacuum‐based drying better preserves phenolics, vitamin C, and aroma. Overall, integrating optimized pre‐treatments with hybrid or energy‐efficient drying technologies can produce superior‐quality dried onion products while minimizing energy use and processing costs, supporting sustainable and scalable industrial drying operations.

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