Chemical composition of common leafy vegetables and functional properties of their leaf protein concentrates

Leaves from four leafy vegetables species: Vernonia amygdalina (Bitter leaf), Solanum africana, Amaranthus hybridus (Green tete) and Telfaria occidentalis (Fluted pumpkins) were subjected to proximate analysis and determination of energy values and nutritionally valuable minerals. Thereafter, leaf protein concentrates (LPCs) were produced from the different species using low-cost fractionation techniques. The LPCs were subsequently characterised with respect to their proximate composition, mineral constituents and functional properties. On average, the leafy vegetables contained 33.3 g/100 g DM crude protein (range 31.7–34.6 g/100 g) and 8.4 g/100 g DM (range, 7.4–9.8 g/100 g DM crude fibre. Gross energy averaged 378 k cal/100 g. The protein extracts contained, on average, 47.2 g/100 g DM crude protein (range 35.1–54.9 g/100 g) 1.4 g/100 g DM crude fibre, 7.9 g/100 g DM ether extract; 15.7 g/100 g DM ash and a gross energy of 439 kcal/100 g. Ca, Mg, Na and K were the most abundant minerals in the leaf meals and leaf protein concentrates while P and Cu were the least abundant. The fat absorption capacity (FAC) varied from 19.0±4.2% in S. africana to 47.0±1.4% in V. amygdalina with a high coefficient of variation (CV) of 49.6%. Similarly, the water absorption capacity (WAC) varied from 149.1±4.8% in V. amygdalina with a CV of 55.0% while emulsion capacity and emulsion stability did not vary much, as indicated by low CVs. The foaming capacity (FC) and foaming stability averaged 8.1% (range 4.1–18.0) and 2.2% (range 2.0–2.9%), respectively. All samples had varying solubilities with change in pH. The proteins generally had multiple maxima and minima in their solubilities. The nutritive potential of the vegetables species and the dietary applications of the protein concentrates are important.