A NOVEL GREEN BIOREFINERY CONCEPT: Protein refining by lactic acid fermentation and biogas production from green biomass

Summary

The extraction of proteins from leaves, integrated in a green biorefinery, may represent an attractive solution to the increasing demand for protein-rich animal feeds while decreasing the dependency on soybean imports. Thereby such green biorefineries could contribute to the development of more self-sufficient and sustainable agricultural systems in Europe. The framework of this PhD study is a green biorefinery concept for the production of protein concentrate, biogas and fertilizer from organic and locally grown green crops like alfalfa, clover or grass. After the screw pressing of the fresh crops, lactic acid fermentation of the green juice with Lactobacillus salivarius BC 1001 was assessed as the key method for the recovery of proteins. A leaf protein concentrate suited as protein feed for monogastric animals is produced, while using a process that is in agreement with the organic production guidelines. In laboratory trials, overall protein recoveries from 12% up to 42% of total plant proteins were achieved in the leaf protein concentrate. The leaf protein concentrates presented relatively high protein contents up to 46% DM, balanced amino acid compositions compared with soybeans and high proportions of essential amino acids for pigs and poultry. Anaerobic co-digestion of the process side stream fractions i.e. press cake and brown juice in the same ratio at which these fractions leave the biorefinery after protein extraction, could recover around 65% of the methane potential in the fresh crops. The protein biorefining process was also evaluated in a demonstration scale plant, processing 444 tons of freshly harvested clover grass continuously during four days and producing 1 ton of dried protein concentrate and 7 tons of protein paste, to be evaluated in large-scale animal feeding trials with laying hens. Besides, the influence of the development stage of the plants over the process yields, protein extractability and production of leaf protein concentrate was investigated. Results indicated that the overall extraction of proteins was reduced with maturity of the plants, and for this reason flowering should be avoided to optimize the production of leaf protein concentrates. Altogether, research outcomes from this study are relevant for the production of protein concentrates from locally grown crops and for further development of green biorefineries in Denmark.