Optimization of drying parameters for maintaining nutritional quality of dehydrated leafy vegetables

Abstract

Leafy vegetables are rich in vitamins, minerals, and antioxidants, but their high moisture content makes them extremely perishable—a problem that costs millions of tonnes in spoilage each year across global supply chains. Drying extends shelf life, yet the heat involved can destroy the very nutrients that make these vegetables worth eating. This research investigated the effect of five drying temperatures (40, 50, 60, 70, and 80°C) on the nutritional quality, colour retention, and rehydration properties of three leafy vegetables: spinach, amaranth, and moringa. Experiments were conducted at the University of Milan food processing laboratories between March and November 2023. Vitamin C retention dropped sharply above 60°C, falling to 38.6% at 80°C, while minerals such as iron and calcium remained relatively stable across all temperatures. Drying at 50°C offered the best balance, retaining 81.4% of vitamin C, 86.7% of β-carotene, and producing acceptable colour change (ΔE = 14.3) with reasonable drying time (9.6 hours for spinach). Moringa leaves showed the highest heat tolerance among the three species. These findings provide practical drying guidelines for small-scale processors seeking to preserve nutritional value in dried leafy vegetable products.