Twin-screw extrusion technology, an original solution for the extraction of proteins from alfalfa (Medicago sativa)

The aim of this study is to develop a new approach to green plant fractionation using twin-screw extrusion, leading to the production of a green filtrate, rich in proteins and a solid fibrous residue, rich in cellulose. The influence of the screw profile on protein recovery in the liquid extract and on plant dehydration was characterized. Two screw profiles were tested, at different temperatures and liquid/solid ratios. Increasing the shearing action on the plant produces a liquid extract richer in protein; from 25% of dry matter to 31% of dry matter when two additional sections of paddle screw elements are inserted onto the screw profile. However, it leads to higher liquid retention in the alfalfa fibers and thus dehydration of the plant is less efficient. The fibrous residue still contains at least 60% humidity when the alfalfa is highly degraded, whereas less than 47% humidity remain with only one section of bilobe paddle screws on the profile. For the two screw profiles tested, the crucial parameter influencing the fraction quality (protein content of the filtrate, dry matter content of the fibrous residue) is the liquid/solid ratio.

► We apply twin-screw extrusion to alfalfa fractionation.
► Protein extraction yields in the green liquid extract are above 50%.
► Twin-screw extruder design is of crucial importance.
► Increasing water quantities added in the extruder could improve protein extraction.