Nutritional value of the kelps Alaria esculenta and Saccharina latissima and effects of short-term storage on biomass quality

Storage of macroalgae in seawater, prior to further processing, is a standard initial pre-treatment step after harvest to avoid rapid degradation of the biomass. In the context of using seaweeds in human food and animal feed products, such practice may affect the nutritional value and the overall quality of the biomass. The effects of seawater storage on the chemical composition (i.e., mineral fraction, carbohydrates, proteins, polyphenols, and fucoxanthin) and surface color of two cultivated kelps (Phaeophyceae), Alaria esculenta and Saccharina latissima, were investigated over a 22-h period.

Storage treatments resulted in a rapid decrease in dry weight during the first 2 h (−21.4 and −20.4% in A. esculenta and S. latissima, respectively) with subsequent stabilization. Although it is not clear whether the reduction of dry weight was caused by the release of nutritional compounds from seaweed biomass or water uptake during storage treatment, the results from chemical analyses suggest the combined effect of both mechanisms. Seawater storage increased the ash and sodium contents and reduced carbohydrate and polyphenol levels in both species.

Among carbohydrates, the levels of mannitol and glucose (laminaran) were particularly reduced in S. latissima samples while the fucose level, reflecting fucoidans, was reduced in A. esculenta. The protein content remained relatively stable in both species. These results provide evidence of the effect of seawater storage on the quality of the edible kelps A. esculenta and S. latissima. The results will contribute to selecting postharvest strategies adequate for maintaining biomass quality, minimizing losses of valuable compounds and increasing profitability for industrial stakeholders.