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Globally, there is an increased demand for sustainable protein sources for animal feed. Grass and forage legumes have the yield potential to become such alternatives, but the protein needs to be separated from the fibres. Red clover, white clover, lucerne and perennial ryegrass were fractionated into a green juice and a fibrous pulp in a screw-press and protein was subsequently precipitated. The nitrogen (N) and amino acid composition of the produced fractions was analysed and the digestibility of dry matter (DM) and N was evaluated using a rat digestibility trial. The aim was to determine the effect of fractionation on composition and digestibility in order to evaluate the four plants as potential protein sources for monogastrics. Protein concentrates with CP concentrations of 240 to 388 g/kg DM and fibrous pulps with CP concentrations of 111 to 216 g/kg DM were produced. The sum of all analysed amino acids was highest in the protein concentrates corresponding to a low concentration of non-protein nitrogen ranging from 4.9% to 10.4%. Only small variations were seen in the amino acid compositions of the different plants and fractions. The concentration of the essential lysine and methionine in the protein concentrate ranged from 6.27 to 6.67 g/16 g N and 1.54 to 2.09 g/16 g N for lysine and methionine, respectively. For all plants species, total tract digestibility of DM and standardised N digestibility was significantly higher in the protein concentrates (60.8% to 76.5% and 75.4% to 85.0% for DM and N, respectively) compared to pulp (21.2% to 43.4% and 52.1% to 72.5% for DM and N, respectively). Digestibility of lucerne protein concentrate (76.5% and 85.0% for DM and N, respectively) was higher than of the unprocessed plant (39.6% and 74.9% for DM and N, respectively), whereas for red and white clover no difference was found. The amino acids methionine and cysteine were limiting for pigs and broilers in all fractions regardless of plant origin, and low scores were also found for lysine. The study demonstrated great potential of using green plants as a protein source for monogastrics because of high protein content, balanced amino acid composition and high digestibility of DM and N. The effects of processing and protein precipitation were pronounced in lucerne where significantly improved digestibility was observed in the protein concentrate. The results from the study provide valuable and enhanced knowledge to the production of alternative and sustainable protein sources for monogastric feed.

A high digestibility of white clover protein was found irrespective of the physical fractionation. Together with a well-balanced amino acid composition, this makes white clover a promising protein source for monogastrics. © 2017 Society of Chemical Industry.

There is a growing need for protein for both feed and food in order to meet future demands. It is imperative to explore and utilize novel protein sources such as protein from leafy plant material, which contains high amounts of the enzyme ribulose-1,5-biphosphate carboxylase/oxygenase (RuBisCo). Leafy crops such as grasses and legumes can in humid climate produce high protein yields in a sustainable way when compared with many traditional seed protein crops. Despite this, very little RuBisCo is utilized for foods because proteins in the leaf material has a low accessibility to monogastrics. In order to utilize the leaf protein for food purposes, the protein needs to be extracted from the fiber rich leaf matrix. This conversion of green biomass to valuable products has been labeled green biorefinery. The green biorefinery may be tailored to produce different products, but in this Review, the focus is on production of food-grade protein. The existing knowledge on the extraction, purification, and concentration of protein from green biomass is reviewed. Additionally, the quality and potential application of the leaf protein in food products and side streams from the green biorefinery will be discussed along with possible uses of side streams from the protein production.