Green leaf biorefining – A demonstrator for production of high-quality food-grade protein

• Food and feed-grade proteins were extracted from leaves using membrane operations • A powder of 58-73% w/w food-grade crude protein with high solubility was isolated • A crude protein yield of ∼5% was achieved for the purified food-grade fraction • A foaming capacity above 150% (at 0.2% w/v) was obtained for the food-grade powder • The pre-filtration-based process was superior to the mild heat pre-treatment process The green transition of the food sector requires new approaches for obtaining high-quality protein products from sustainable plant sources. Among these, green biomass represents an underutilised resource as current production methods rely on energy-intensive processes that promote protein denaturation, resulting in products with reduced functionality and low applicability value. This work focuses on the recovery of protein from clover grass using gentle and non-destructive membrane separation in demonstrator-scale (14-25 kg of fresh leaves). Green juice was extracted using screw pressing followed by either 1) heat treatment and centrifugation or 2) pre-filtration. Subsequently, the juice was separated by two-step crossflow membrane filtration. The first filtration produced a retentate, applicable for feed production, and a permeate free from grassy sensory attributes and green colour, which was further fractionated in the second filtration and purified by diafiltration to produce food protein powder. A food protein powder with high crude protein content (58-73% w/w), corresponding to a yield of ∼5% w/w (based on crude leaf protein) was recovered using the pre-filtration process option. This represents substantial improvement compared to the heat-pretreatment option (12-28% crude protein content). The powder lacked grassy smell/taste and displayed high aqueous solubility and excellent foaming properties. The powder properties were similar over the season and largely unaffected by variations in process parameters while effects on yields were more pronounced. This work represents a substantial advancement in green biorefining and showcases the potential of membrane operations towards full and multi-purpose utilisation of sustainable bioresources.