Acid preservation of Saccharina latissima for application as a carbon source for fermentation to biofuels and chemicals

Cultivated kelps (brown algae) are a sustainable biomass resource and a potential feedstock for conversion to biofuels and chemicals. Due to seasonal variations, and a short period with optimal biomass composition, preservation and storage of the biomass is required for a year-round operation of a seaweed processing plant. For use of the biomass as a carbon source for fermentation to biofuels, only low-cost preservation methods are feasible. Preservation of Saccharina latissima (sugar kelp) by sulphuric and formic acid has been evaluated as a method to maintain the fermentable carbohydrates laminaran and mannitol. In milled biomass, stored anaerobically for up to 6.5 months at different pH values, laminaran and mannitol were efficiently preserved in samples stored at pH below 3.7, obtained by addition of sulphuric acid. When a combination of sulphuric and formic acid was used, no sugar loss could be detected up to pH 4. The content of free glucose increased during the storage period in the well-preserved samples without loss of sugars. The free glucose levels were highest at the highest storage pH, providing strong evidence for the presence of endogenous β- glucanases that hydrolyse laminaran to glucose. Our work was primarily aimed at preservation of the biomass for application as a carbon source for fermentation. However, the method will be equally suited for other applications of the biomass, such as extraction of valuable compounds for use in functional food, feed or other areas.