Influence of Thermal Processing on Proximate Composition and Functional Properties of Selected Green Leafy Vegetable Powders

Abstract

Green leafy vegetables (GLVs) are nutrient-dense foods with potential for use in dehydrated forms; however, processing conditions may influence their composition and functional characteristics. This study evaluated the effect of thermal processing on the proximate composition, functional properties and qualitative phytochemical profile of selected green leafy vegetable powders prepared from Agathi leaf (Sesbania grandiflora), Ponnangani leaf (Alternanthera sessilis) and curry leaf (Murraya koenigii). Fresh leaves were cleaned, subjected to selected cooking treatments, namely boiling, simmering and steaming, and dried in a cabinet drier at 60°C for 4-5 hours. Untreated dried leaves served as the control. The powdered samples were analysed for moisture, crude protein, mineral content, crude fibre, bulk density, water absorption capacity, oil absorption capacity, emulsifying activity, foaming capacity and selected phytochemicals. The dehydrated control powders contained 3.90-7.53% moisture, 22.31-35.59 g/100 g crude protein, 9.06-18.94 g/100 g minerals and 8.13-15.60 g/100 g crude fibre. Cooking before drying influenced the composition and functional behaviour of the powders, with variations depending on the vegetable type and treatment applied. Protein content was comparatively high in Agathi and Ponnangani powders, while curry leaf powder showed higher crude fibre. Water absorption and oil absorption capacities varied among treatments, indicating possible changes in hydration and lipid-binding properties after thermal processing. Qualitative phytochemical screening showed the presence of several phytochemicals, including phenols, steroids, alkaloids, glycosides, saponins, tannins, quinones, flavonoids and coumarins, whereas anthocyanins were not detected in the tested samples. The findings indicate that dehydration, under suitable processing conditions, may support the preparation of green leafy vegetable powders with useful nutritional and functional properties.