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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 an increasing interest in green biorefineries for the utilization of green biomass to provide a variety of valuable products. Proteins can be extracted from green biomasses such as alfalfa, clover, or grass and separated into protein‐rich concentrates suitable for feeding to monogastric animals. Press cake suitable for feeding ruminant animals is also produced. Full implementation of such a green biorefinery requires knowledge and experience of production at demonstration scale. Moreover, product evaluation in animal‐feeding trials requires a large amount of product. There has been collaboration in Denmark between several partners from industry and academia to assess the practicality and scalability of a green biorefining plant producing protein concentrate and press cake silage from organic grass clover at the scale of ca. 10 tons per hour fresh biomass input. Lactic acid fermentation of the pressed green juice was successfully performed to precipitate proteins and stabilize the juice. Despite minor difficulties, the demonstration‐scale biorefining plant was operative for four days, processed 444 tons of grass clover, and resulted in the overall production of 1 ton of dried protein concentrate, 7 tons of protein paste, and 223 tons of press cake silage. The protein concentrate was rich in essential amino acids and was tested in feeding trials with poultry; the press cake silage, rich in processed fibers and fiber‐associated proteins, was tested in feeding trials with dairy cows. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd