Biorefinery of the green seaweed Ulva lactuca to produce animal feed, chemicals and biofuels

The growing world population demands an in- crease in animal protein production. Seaweed may be a valu- able source of protein for animal feed. However, a biorefinery approach aimed at cascading valorisation of both protein and non-protein seaweed constituents is required to realise an eco- nomically feasible value chain. In this study, such a biorefinery approach is presented for the green seaweed Ulva lactuca containing 225 g protein (N × 4.6) kg−1 dry mat- ter (DM). The sugars in the biomass were solubilised by hot water treatment followed by enzymatic hydrolysis and centri- fugation resulting in a sugar-rich hydrolysate (38.8 g L−1 sugars) containing glucose, rhamnose and xylose, and a protein-enriched (343 g kg−1 in DM) extracted fraction. This extracted fraction was characterised for use in animal feed, as compared to U. lactuca biomass. Based on the content of essential amino acids and the in vitro N (85 %) and organic matter (90 %) digestibility, the extracted fraction seems a promising protein source in diets for monogastric animals with improved characteristics as compared to the intact U. lactuca. The gas production test indicated a moderate rumen fermentation of U. lactuca and the extracted frac- tion, about similar to that of alfalfa. Reduction of the high content of minerals and trace elements may be required to allow a high inclusion level of U. lactuca products in animal diets. The hydrolysate was used suc- cessfully for the production of acetone, butanol, ethanol and 1,2-propanediol by clostridial fermentation, and the rhamnose fermentation pattern was studied.