ProFA - Valorization of macroalgae biomass as source of proteins and formic acid

Abstract

Macroalgae are promising feedstocks for the sustainable production of bioplastic films from proteins or platform chemicals such as formic acid as they are valuable sources of proteins and carbohydrates. This study explores the possibility of using macroalgae as biomass for biogenic formic acid production with the OxFA process in combination with the extraction of proteins from macroalgae with a focus on resource utilisation and innovation. This study is the first to link the extraction of proteins and the utilisation of the other components of macroalgae to produce formic acid as another valuable product. The aim was to find out which macroalgae is best suited to produce formic acid and protein-rich solids. To this purpose, three different algae from three different groups were tested: The brown alga Fucus vesiculosus, the green alga Ulva fenestrata and the red alga Porphyra dioica. In addition, the most suitable catalyst for this study was selected from the two polyoxometalates H5PV2Mo10O40 (HPA-2) and H8PV5Mo7O40 (HPA-5) known for their effective oxidation of biomass to formic acid. After Porphyra dioica proved to be a promising substrate, the parameters temperature (80 °C – 120 °C), time (18 h – 30 h) and catalyst/substrate ratio (0.05 to 0.5) were tested for their statistical influence using a Box-Behnken design of experiments. The resulting model was then used to optimise the protein content and formic acid yield. These optimal conditions were 80 °C, 30 hours and a catalyst-to-substrate ratio of 0.5. The optimised experiment resulted in a protein yield of 59.5 % and a formic acid yield of 16.4 %. For protein extraction from solid residues, three different methods such as alkaline hydrolysis, ultrasound-assisted extraction (UAE) and ionic liquid extraction (ILE) were investigated. All extraction methods resulted in a protein recovery of more than 40 %dw from solid residues, with ultrasound-assisted extraction yielding the highest protein recovery of 87.2 %dw (at 100 % sonication amplitude). UAE resulted in 30 % higher protein recovery than alkaline hydrolysis and 40 % higher protein recovery than extraction with ionic liquid extraction. It was concluded that the OxFA process followed by protein extraction of UAE gave a high protein recovery and a medium yield of formic acid.