Controlled Solar Drying Systems for Valorizing Neglected and Underutilized Vegetables in Arid Ecosystems: Performance, Quality, and Sustainability Perspectives

Abstract

Arid regions face severe food insecurity due to harsh climatic conditions, limited water resources, and fragile agricultural systems. Neglected and underutilised vegetables (NUVs) cultivated in arid ecosystems are climate-resilient, highly nutritious, and possess immense potential to combat malnutrition and hidden hunger. However, NUVs poses short shelf life, and the absence of suitable post-harvest management and storage systems leads to 20–40% losses, exacerbating the food crisis. Conventional drying methods rely on fossil fuels or grid-dependent energy, which are scarce and unaffordable in remote arid areas, resulting in continued reliance on open-sun drying (OSD), which is associated with prolonged drying periods, uncontrolled thermal exposure, fluctuating humidity, contamination risks, and significant nutrient degradation. This review critically evaluates controlled solar drying systems capable of regulating key parameters to enhance drying kinetics and process stability. Under arid conditions, these systems typically maintain drying air temperatures of 45–75 °C and achieve effective moisture diffusivity in the range of 10⁻⁹–10⁻⁷ m²/s, reducing drying time by 30–60% compared to open-sun drying while improving moisture uniformity, nutrient retention, and microbial safety. Beyond technical performance, controlled solar drying contributes to shelf-life extension, value addition, rural income generation, and low-carbon food processing. Unlike existing solar drying system reviews that primarily focus on commercially cultivated crops, this review uniquely synthesizes controlled solar drying for NUVs in arid ecosystems, integrating performance metrics, quality preservation, and sustainability within a broader food security framework.