Brown seaweed processing: enzymatic saccharification of Laminaria digitata requires no pre-treatment

Carbohydrates from brown macroalgae (brown seaweeds) have received increased attention as a new biomass resource for biofuels and manufacture of high-value carbohydrate products. Seaweeds harvested in the Northern hemisphere in late summer are potentially dominated by glucans while the main matrix polysaccharide alginate is partially low. This, along with mannitol and comparable low ash contents make them predestinated for application in biorefineries.

Wet refiner milling as physical pretreatment of brown seaweed Laminaria digitata with high glucan (laminarin) content of 51 % led to particle size reduction with degree of milling. By using rotating disc distances of 0.1-2 mm differently sized particle populations of average surface areas from 100-0.1 mm² were generated. Higher milling degree caused increased spontaneous carbohydrate solubilization in the milled seaweed slurries, but diminution of particle size did not improve the enzymatic glucose release. Milling was thus not required for enzymatic saccharification because all available glucose was released even from the non-milled material with a mixture of alginate lyase and a commercial cellulase preparation (Cellic®CTec2). Enzyme dosage of 1 % (w/w) alginate lyase and 10 % (v/w) Cellic®CTec2 released the potential glucose during 8 hours treatment, and two-thirds of the glucose was released with lower enzyme loading already. The alginate lyase catalysis apparently induced both selective degradation of the cell wall alginate and decreased the viscosity to promote enzymatic laminarin saccharification. Application of the cellulase preparation alone released only half of the available glucose.