Ensiling of sugar kelp biomass for biorefining

Ensiling was investigated as a long-term storage method for preserving brown seaweed biomass (sugar kelp, Saccharina latissima (Phaeophyceae)) for subsequent use e.g. in a year-round biorefinery context where value-added constituents should be recovered for further formulation. Sugar kelp ensiling trials were carried out in lab-scale and pilot-scale with up to one-year duration, by either biological ensiling by means of lactic acid bacteria (LAB) fermentation or by chemical ensiling by addition of lactic acid to reduce pH. The results clearly demonstrated that the ensilability of sugar kelp was positively correlated with the initial glucose content which was partly consumed by LAB for obtaining and maintaining low pH. The ensiling process could be optimized by initial addition of molasses and further by addition of commercial LAB inoculum. The dose of molasses was important for pH development during biological ensiling. Similarly, initial addition of lactic acid was important for obtaining an effective chemical ensiling. Biological ensiling reduced the content of native glucose from sugar kelp and increased the content of fermentation products, primarily lactic acid. Addition of either molasses + LAB inoculum or lactic acid reduced the degradation of total amino acids during ensiling. Freezing prior to ensiling hampered the ensiling process but could be compensated for by addition of LAB. In conclusion, ensiling can be used for long-term storage of seaweed biomass, however, the ensiling process alters the biomass composition and, hence, the quality for subsequent use in biorefinery processes. The fate of higher-value components during ensiling needs further investigation.