Approximately 1 billion tons of food are thrown away yearly, resulting in a significant loss of renewable nutrient sources. Moreover, there is growing interest in developing new products from sustainable plant protein alternatives, such as lentils, to tackle environmental and health challenges. Hence, this study aimed to explore the potential of protein concentrates obtained from green lentil waste flour (LWF) as a novel protein ingredient. The protein concentrates were recovered via alkaline extraction (pH 9, ratio 1:5 flour/solvent + 0.1M of NaCl) and centrifugation, followed by ultrafiltration (UF). UF performance was evaluated on a bench-scale, pressure-driven, cross-flow filtration membrane unit using a 100 kDa cut-off. The protein-rich UF concentrate at a Volume Concentration Ratio (VCR) of 6.00 was evaluated regarding composition, physicochemical properties, and protein profile. Furthermore, their viscoelastic and gelling properties were determined. The UF decreased flux due to polarisation and fouling, with values reaching 1.28 l/m²h at VCR 6.00. A concentrate with a protein content of ~80% (w/w d.m.) was obtained. SDS-PAGE allowed for the identification of the protein profile, consisting of convicilin (65 kDa), vicilin subunits (55-45 kDa), acidic and basic legumin subunits (visible under reducing conditions), and albumin (~ 17 kDa). The gelling temperature was 72.50°C, with G’ being higher than G’’, suggesting a viscoelastic behaviour. When the power law was applied, the frequency sweep test showed low n-values (G’ - G’’< 0.2), indicating minimal frequency dependence and structural integrity. Strain sweep tests showed a linear viscoelastic region of 12.76 with a mild weak overstrain shoot on G’’, typical of weak gels. To conclude, LWF can be valorised into a protein-rich ingredient, with UF yielding an 80% protein concentrate while maintaining structure and functional properties, making it suitable as an ingredient in the food industry.