Early-Stage Life Cycle Assessment and Optimization of Aqueous Crude Glycerol Extraction and Nanofiltration Concentration of Tomato Leaf Residue

This study explored the potential of aqueous crude glycerol as a solvent to extract phenolics from tomato leaf residue (TLR) and nanofiltration for the concentration of the extract. The crude glycerol content, liquid-to-solid ratio, and extraction temperature were optimized by response surface methodology. The optimum conditions provided satisfactory results for the total phenolic content (204.51 ± 2.31 mg of gallic acid equivalents/g TLR dry weight), 2,2-diphenyl-1-picrylhydrazyl scavenging activity (58.03 ± 2.00%), and total flavonoid content (41.44 ± 0.10 mg of rutin/g TLR dry weight). Then, the individual phenolics in the crude extract were identified and concentrated by nanofiltration. To increase the permeation flux and improve the concentration efficiency of the phenolic compounds, the membrane performance was evaluated at different transmembrane pressures. Considering the concentration of quercetin (113.74 mg/L), filtration time, and cleaning efficiency, a transmembrane pressure of 1.5 MPa was selected. A life cycle assessment of the entire process showed that electricity was responsible for a significant portion of the environmental impacts, and the hydrothermal extraction process was the most influential.