Valorisation of marine macroalgae waste using a cascade biorefinery approach: Exploratory study

The present study aims to assess the potential exploitation of marine macroalgae waste using a cascade biorefinery approach. For that, biomass was collected from a northern Portugal beach, two different drying processes were employed (freeze-drying (FD) and sun-drying (SD)) and cascade extractions were conducted to obtain several extracts (fatty acids, pigments, polysaccharides) and a final extraction residue that were further characterised. The results show that the drying process affects the most sensitive compounds – e.g., pigments (fucoxanthin only detected in FD samples: raw biomass (1.1 mg.L−1) and polar cascade extract (1.5 mg.L−1)) – due to degradation processes, whereas the polymers, sugars and minerals are not affected. Carbohydrates, the prevailing compounds in marine macroalgae waste, are mainly composed by galactose and glucose. By comparing with the use of raw biomass, cascade extractions have a higher impact in the concentrations of monosaccharides and uronic acids (results from 28 up to 130 mg g−1; about fourfold and threefold higher for FD and SD extracts, respectively) and total minerals (results from 2417 up to 4507 mg.100 g−1; 1.6 and 1.4 higher for FD and SD final residues, respectively). This was not observed for the non-polar extracts due to the different extraction procedures and the low lipid content (maximum of 9.96 mg of fatty acids per gram, in the SD raw biomass). The mineral fraction was mainly composed by calcium, potassium, sodium and magnesium. The presence of alginic acid and other sulphated polymers and the low content of red seaweed polymers reflects the fact that the biomass is mainly composed by brown species. Taking into account the objective of exploring the full use of marine macroalgae waste to obtain diverse products with economic and environment advantages, also considering product quality increase and the absence of final residues, the application of the cascade process seems to be the most desirable route. The freeze-drying process should be further explored.