Membrane selectivity during the production of food and feed proteins from clover grass juice

Extraction and recovery of locally produced plant-based leaf proteins, through a biorefinery approach, is a promising pathway towards increased sustainability during food and feed production. Separation and utilisation of the two protein fractions, a fraction of “green” protein (e.g. chlorophyll-binding and biomembrane-bound proteins) for animal feed purposes and a fraction of “white” protein (mainly RuBisCO) for human consumption, is central for the sustainability as well as economic viability of any such biorefinery process. Membrane filtration has been suggested to achieve this separation. While membrane-based operations offer important advantages in terms of avoiding possible protein denaturation and retaining high protein solubility, membrane fouling has proven to be a significant obstacle, as it both reduces capacity and changes selectivity. This work studies the separation characteristics of clover grass juice, especially selectivity, during 60 nm ultrafiltration on a kg scale, where green protein-rich feed fractions are separated from white protein-rich food fractions. The results show that after a rapid initial flux decline, a region of slower flux decline occurred as the filtration progressed, with an average permeate flux of around 22 L/(m 2 ·h) at a volumetric concentration factor of 3. Apparent rejection of crude protein in the clover grass juice was found to be higher than the corresponding rejection of juice dry matter, with rejections of 52% and 33% on average, respectively. Furthermore, proteomics revealed that chlorophyll-binding proteins and photosystem proteins were very efficiently rejected (>99%), which corresponds well with the successful retention of green colour from leaf juice. • Proteomics was used as a novel approach to study selectivity during ultrafiltration. • On average, fluxes of 22 L/(m 2 h) at a VCF of 3 (TMPs ~0.3 bar) were observed. • The rejection of crude protein was higher than the average rejection of components. • RuBisCO, a promising food protein, was the most abundant protein in the permeate. • Chlorophyll-binding proteins and photosystem proteins were highly retained (>99%).