Enhancing protein recovery in green biorefineries through selection of plant species and time of harvest

Abstract

Biorefining is a promising method for sustainable feed production through conversion of biomass into a protein concentrate for monogastrics and fibrous pulp for ruminants. Nitrogen (N) content and recovery in pulp and protein concentrate from lucerne, red clover, white clover, perennial ryegrass and tall fescue harvested at different spring cut harvest times were analysed to assess the effect of plant species, developmental stage and number of screw press processing.Plant species and spring cut harvest time affected N content of pulps and protein concentrates (P < 0.01). The N contents of the legume pulps and protein concentrates (22.0–43.2 g/kg dry matter (DM) and 52.1–68.9 g/kg DM, respectively) were higher than corresponding values of the grasses (16.4–31.2 and 38.1–58.9 g/kg DM, respectively) and lowest in late harvested pulps (16.4–29.2 g/kg DM). The proportion of N retained in pulp increased with spring cut harvest time (P < 0.01) and was higher in grasses compared to legumes (544.5–715.1 and 334.0–565.2 g/kg plant N, respectively). Plant species and spring cut harvest time affected N recovery in protein concentrate (P < 0.01) and correlated positively with the plant N content (P < 0.01) and negatively with the plant DM (P < 0.01). The legumes had a higher recovery than grasses (160.2–556.2 g/kg plant N and 160.2–335.6 g/kg plant N, respectively). Regardless of plant species, late spring cut harvests reduced the total N extractability, i.e. recovery after application of a two-step extraction procedure, to 342.8–490.9 g/kg plant N (P < 0.01). The largest proportion of N was extracted from the three legumes (458.4–653.8 g/kg plant N), with the lowest extractability in the late spring cut harvest.The N content and recovery in fractions produced in the biorefining process were dynamic variables influenced by plant species, spring cut harvest time and number of screw press processings. More N was retained in the pulp from late cut grasses whereas the N recovery in protein concentrate was highest in early and intermediate cuts from legumes. The dynamics of N distribution between pulp and protein concentrate highlight the importance of considering input plant species, time of harvest and processing technique in order to enhance recovery and secure efficient utilisation of the biomass as feed for monogastrics and ruminants.