Gregersen Echers, S.; Abdul-Khalek, N.; Jensen, N. H.; Jorgensen, A. K.; Mattsson, T.; Jorgensen, M. K.; Lubeck, P. S.; Lubeck, M.

Green leaves are gaining traction as an emerging protein source and a sustainable alternative to animal-based protein as leaf proteins often possess good nutritional and functional properties. Current methods for producing protein isolates from leaves include partially or fully denaturing conditions, diminishing protein solubility and functionality. Here, we characterize the performance of a multi-stage, membrane-based green biorefinery concept capable of producing a native protein product from clover grasses devoid of attributes such as green color and grassy smell/taste. By sampling at each step along the process, we obtain insights on the fate of proteins and pigments over each unit operation. The process efficiently removes green pigments (>99.9%), when comparing the product stream with the initial feed stream, based on UV/Vis analysis. Using mass spectrometry-based proteomics, two complementary quantification strategies, and subsequent bioinformatic analysis, this can particularly be ascribed to a very selective retention (>99%) of unwanted membrane-associated and pigment-binding proteins in the first-stage filtration. In the second-stage filtration and subsequent diafiltration stage, residual unwanted proteins, fragments, and pigments are efficiently washed out while retaining the overall protein composition. The product maintains the high RuBisCO content of green juice and is furthermore enriched in proteins with known antioxidant properties while depleted in known food allergens. This work presents an in-depth understanding of protein-level selectivity in membrane-based green biorefinery and can help guide process optimization towards improved yields and quality.