A fractionation strategy for Saccharina latissima algal biomass was developed utilizing chelating extraction salt solutions to mediate the liberation of algal components. Alginate, cellulose, laminarin, mannitol, protein, and inorganic salts were quantified in the fractions to reveal their individual dissolution patterns. Chelation power was identified as a key parameter for liberating alginate and increasing the yield of extracted components. The most efficient fractionation was achieved using aqueous sodium citrate as the extraction solution, producing an alginate-rich soluble fraction and a salt-poor insoluble fraction rich in cellulose and protein. Extractions at decreased pH were shown to be beneficial because they decreased the M/G ratio of the extracted alginate and concentrated the protein in the insoluble fraction from which it can easily be recovered; these effects could be achieved by switching the traditional sodium carbonate extraction solution with salts that have chelation capacity at lower pH. A cyclic extraction demonstrated that the sodium citrate solution can be reused for multiple alginate extractions with the buildup of the concentrations of other valuable components in the solution.

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A new approach to process Saccharina latissima algal biomass was developed using sodium citrate and a polyvalent cation-specific resin to sequentially extract the alginate into several usable fractions. The fractionation was performed in a cyclic manner, utilizing a stepwise removal of the native polyvalent ions present in the algae to isolate fractions of alginate with different solubility in the presence of these ions. Sodium citrate was used in different concentrations in the extraction solution to remove polyvalent cations to adjust the alginate liberation while AMBERLITE IRC718 resin was added to further remove these ions and regenerate the extraction solution. Alginate was recovered by acid precipitation and analyzed for its uronic acid composition and molecular weight, and the carbohydrate compositions of the insoluble and soluble parts of the algal biomass residue were determined. Finally, the fractionation method was assessed with a life cycle analysis to determine the energy and water efficiency as well as the greenhouse gas emissions and the results were compared to conventional alkaline extraction. The results indicate that the energy and water use as well as the emissions are considerably lower for the cyclic extraction in comparison with the conventional methods.Electronic supplementary materialThe online version of this article (doi:10.1007/s10811-017-1176-5) contains supplementary material, which is available to authorized users.

Laminarin is a low-molecular-weight polysaccharide found in seaweed (kelp), often in equal concentrations to that in the commercially important hydrocolloid alginate. However, while alginate can be easily recovered by dissolution followed by acid precipitation, for laminarin, there is no such straightforward way of recovering it. Laminarin can be used as dietary fiber and, if efficiently extracted, it may be used for functional food/feed applications and as a component in plant defense stimulants for agriculture. One way of concentrating laminarin from dilute solutions is to press the solution through ultrafine membranes that the molecules cannot pass through. When alginate is extracted, an acid pretreatment step is used and the dilute acid residue from that process also contains laminarin. We used cross-flow filtration to concentrate laminarin from Saccharina latissima, retrieving it from the dilute acid solution of the acid pretreatment of an alginate extraction. Three ceramic membranes with 5, 15, and 50 kDa molecular weight cutoffs were used, and the pressure, temperature, and feed velocity were altered to reveal which parameters controlled the flow through the membrane and how efficiently laminarin was concentrated. The effects on laminarin extraction for fresh vs. frozen biomass were evaluated showing that frozen biomass releases more laminarin with a similar biomass homogenization technique. Thermal and microbial degradation of the feed components was studied during the course of the filtrations, showing that microbial degradation can affect the laminarin concentration, while the temperature of the process ~ 65 °C had little impact on laminarin. The techniques used to monitor the components in the feed and permeate during filtration were nuclear magnetic resonance, 1H-NMR, and size exclusion chromatography. The filtrations were performed in a pilot-size filtration unit with ceramic membranes (ZrO2/TiO2, TiO2-Al2O support, 0.08 m2). To be able to operate without quick membrane fouling, the most important parameter was to have a high liquid velocity over the membrane, 4.7 m s−1. A good technique to concentrate laminarin was to prefilter it through a 50-kDa membrane using 2 bar liquid pressure and to concentrate it over a 5-kDa membrane using 5-bar liquid pressure. With these settings, the liquid flux through the filter became 60–80 and 30–40 L m−2 h−1 over the 50-kDa and 5-kDa membrane.

Kelps can be included in integrated multitrophic aquaculture (IMTA) where their growth and quality might benefit from the nutrient load released by other species like finfish and mussels transforming effluents from the cultured animals into valuable products. We studied how different nutrient concentrations affect growth, photosynthesis, chemical composition and pigment content of the kelp Saccharina latissima. We exposed kelps to natural seawater, water enriched to levels of ammonium and nitrate simulating finfish cage waste (IMTA1) and a combination of such enrichment with natural effluents coming from mussels (IMTA2). The algal biomass was higher and produced elevated total organic content when exposed to both IMTA1 and IMTA2. The photosynthetic responses in terms of relative electron transfer rate (rETRmax), PSII saturation irradiance (Ek) and total nitrogen content were also positively affected by both IMTA1 and IMTA2. We found a significant enhancement in pigment content only when algae were exposed to the strongest enrichment of our study (IMTA2). Finally, we found a positive relationship between rETRmax and growth, and the content of chlorophyll a and fucoxanthin. Our results show significant physiological responses of S. latissima to nutrient enrichment mimicking IMTA settings, as well as the benefit of added nutrients through a boost in photosynthetic activity that leads to higher kelp biomass and pigment production. This study suggests that modest nitrogen enrichment such as the one in our IMTA2 setup is enough to generate not only higher kelp biomass, but also an increased biomass quality with potentially higher market value.