Impact of postharvest osmodehydration treatments and drying processes on the nutritional quality, bioactive compounds and preservation of leaf amaranth (Amaranthus cruentus)

Amaranth leaves are rich in micronutrients and health-promoting secondary metabolites, but highly perishable. The effect of osmodehydration and drying on nutritional quality, health-promoting compounds and their postharvest preservation in Amaranthus
cruentus leaves was investigated. The experimental set up consisted of four treatment variants with different levels of osmotic solution (NaCl) concentration, temperature and immersion time, i.e.; variant 1 (2.5%, 20 °C, 60 min), variant 2 (10%, 20°C, 60 min), variant 3 (10%, 40°C, 60 min), and variant 4 (10%, 40°C, 180 min). Osmodehydrated leaves were oven-dried at 30°C or 60°C, freeze-dried or stored at ambient temperature for 3 days, with non-osmodehydrated leaves as control. Results showed that proteins,minerals (Ca, Mg, Fe, Zn), carotenoids, flavonoids, and phenolic acids were preserved in osmodehydrated leaves with no significant changes, except proteins in freeze-dried and a significantly decreased chlorophyll content in both freeze- and oven-dried leaves of variant 4, corresponding to higher osmotic solution concentration, temperature and longer immersion time. During shelf-life, most nutrients and secondary metabolites were maintained with no significant changes, except protein that significantly increased while ascorbic acid and chlorophylls in both osmodehydrated and control leaves significantly decreased. Lower-temperature and shorter-time immersion resulted in better quality preservation.