Novel uses of ensiled biomasses as feedstocks for green biorefineries

Perennial forage plants are efficient utilizers of solar radiation and nutrients so that there is a lot of scope to increase the production of green biomass in many areas. Currently, grasses are mainly used as feeds for ruminants and equines, but there could be higher added value use for several components of the green biomass. Interest in green biorefining has risen recently motivated by the increased sustainability pressures and need to break the reliance on fossil fuels. Novel products derived from grass, such as paper and packaging, nanofibers, animal bedding, novel protein feeds, extracted proteins, biochemicals, nutraceuticals, bioactive compounds, biogas and biochar could create new sustainable business opportunities in rural areas. Most green biorefinery concepts focus on using fresh green biomass as the feedstock, but preservation of it by ensiling would provide several benefits such as all-year-around availability of the feedstock and increased stability of the press juice and press cake. The major difference between fresh and ensiled grass is the conversion of water soluble carbohydrates into fermentation end products, mainly lactic and acetic acids, that lower the pH of the silage so that it becomes stable in anaerobic conditions. This has some important consequences on the processability and quality of products, which are partly positive and partly negative, e.g., degradation of protein into peptides, amino acids and ammonia. These aspects are discussed in this review.