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Brown macroalgae are an important source of polysaccharides, mainly fucose-containing sulphated polysaccharides (FCSPs), associated with several biological activities. However, the structural diversity and structure–function relationships for their bioactivities are still undisclosed. Thus, the aim of this work was to characterize the chemical structure of water-soluble Saccharina latissima polysaccharides and evaluate their immunostimulatory and hypocholesterolemic activities, helping to pinpoint a structure–activity relationship. Alginate, laminarans (F1, neutral glucose-rich polysaccharides), and two fractions (F2 and F3) of FCSPs (negatively charged) were studied. Whereas F2 is rich in uronic acids (45 mol%) and fucose (29 mol%), F3 is rich in fucose (59 mol%) and galactose (21 mol%). These two fractions of FCSPs showed immunostimulatory activity on B lymphocytes, which could be associated with the presence of sulphate groups. Only F2 exhibited a significant effect in reductions in in vitro cholesterol’s bioaccessibility attributed to the sequestration of bile salts. Therefore, S. latissima FCSPs were shown to have potential as immunostimulatory and hypocholesterolemic functional ingredients, where their content in uronic acids and sulphation seem to be relevant for the bioactive and healthy properties.

The aquaculture of macroalgae for human consumption and other high-end applications is experiencing unprecedented development in European countries, with the brown algae Saccharina latissima being the flag species. However, environmental conditions in open sea culture sites are often unique, which may impact the biochemical composition of cultured macroalgae. The present study compared the elemental compositions (CHNS), fatty acid profiles, and lipidomes of S. latissima originating from three distinct locations (France, Norway, and the United Kingdom). Significant differences were found in the elemental composition, with Norwegian samples displaying twice the lipid content of the others, and significantly less protein (2.6%, while French and UK samples contained 6.3% and 9.1%, respectively). The fatty acid profiles also differed considerably, with UK samples displaying a lower content of n-3 fatty acids (21.6%), resulting in a higher n-6/n-3 ratio. Regarding the lipidomic profile, samples from France were enriched in lyso lipids, while those from Norway displayed a particular signature of phosphatidylglycerol, phosphatidylinositol, and phosphatidylcholine. Samples from the UK featured higher levels of phosphatidylethanolamine and, in general, a lower content of galactolipids. These differences highlight the influence of site-specific environmental conditions in the shaping of macroalgae biochemical phenotypes and nutritional value. It is also important to highlight that differences recorded in the lipidome of S. latissima make it possible to pinpoint specific lipid species that are likely to represent origin biomarkers. This finding is relevant for future applications in the field of geographic origin traceability and food control

The continuing expansion of seaweed cultivation could assist in ensuring future global food security. The Laminariales species Alaria esculenta and Saccharina latissima are each cultivated for food across their European ranges. The predominant method for cultivating European kelps involves growing juveniles on twine within a hatchery which is then deployed at a farm site. The associated hatchery and deployment cost of this approach are relatively high. A new and innovative methodology—called binder-seeding—can reduce these costs, but, has yet to be validated. We compare the biomass yield and morphology of A. esculenta and S. latissima cultured using either the traditional twine-longline method or binder-seeding onto AlgaeRope and AlgaeRibbon, specially designed textiles. In a controlled growth experiment, A. esculenta had a similar biomass yield on all materials, but fronds were shorter (23 ± 7%) and thinner on the AlgaeRibbon (42 ± 4%) due to a 3–4-fold higher density of developing sporophytes compared to the twine-longline. In contrast, S. latissima gave a 4-fold higher biomass yield on the AlgaeRibbon in June (4.0 kg m−1), but frond morphology was not different between materials, despite a 4-fold higher sporophyte density on the AlgaeRibbon. The stipe length of both species also increased at the higher sporophyte density on the AlgaeRibbon. The AlgaeRope gave an intermediate response or was similar to the twine-longline. These results show that binder-seeding onto the AlgaeRibbon significantly increases the achieved biomass yield in S. latissima. These results can assist cultivators to select the most appropriate method of kelp cultivation depending on morphological/yield requirements of the end use. Further study is needed on the optimisation of the binder-seeding density and its impact on thallus morphology.

The phaeophyte macroalgae Sargassum muticum is under investigation as a cultivation crop within its native range in SE Asia, alongside other members of the Sargassum genus. During the critical hatchery phase, germlings are grown to ≥ several millimeters ready for outplanting. By optimising the growth medium and twine substrate used for the germling attachment, hatcheries can become more efficient and cost-effective. An 8-week replicated laboratory experiment investigated these factors. It found that adding 0.125 mL L−1 of saturated germanium dioxide during the first week increased mean germling size by 23% (p < 0.005), whereas additional nutrients in the form of F/2 medium made no difference (p > 0.05). Six twine substrates were also tested: jute, cotton, polyamide/cotton, polyester, polyvinyl alcohol and polypropylene. Sargassum muticum grew similarly well on all, although attachment success during the first week was highest on the rougher natural fibres, particularly jute. A negative density-dependent effect of germling density on growth was seen across all materials, with the highest growth seen on the materials with the lowest germling density. Jute is recommended as a highly suitable substrate for hatchery cultivation in this species, although the initial density should be carefully controlled to prevent intraspecific competition.

The predominant method used for the cultivation of European kelp involves seeding onto twine spools. The selection of a suitable twine is essential. In four experiments, synthetic and natural polymer twines were seeded with either meiospore or juvenile sporophytes of Saccharina latissima. Development was monitored over both the hatchery and outplanting phase at an experiment seaweed farm, Scotland, UK. Twisted twine seeded with meiospores gave 37 ± 21% higher biomass yield than the braided form, despite 46 ± 10% lower sporophyte density during the hatchery period. Twisted twine was also more favourable when sporophyte seeding, increasing juvenile retention by 140%. Three-month-old sporophytes had 50% weaker bioadhesion on polyamide (PA), polyester (PES) and polypropylene (PP) compared to polyvinyl alcohol (PVA). This was reflected in 11–24% higher biomass on PVA following outplanting. However, if the twine surface was treated by corona discharge before seeding, PA, PES and PP achieved an equivalent biomass to PVA. Jute and sisal twine had a toxic effect on the development of meiospores. In contrast, seeding with sporophytes was successful onto jute and sisal, but bioadhesion was weak. Finally, cotton was moderately toxic to meiospores but also had a bioadhesion strength and biomass yield comparable to PVA. We conclude that PVA and corona-treated synthetic twines are excellent for either meiospore or sporophyte seeding. Cotton is a very promising biodegradable twine, although further research is needed to optimise its physical structure. We also conclude that results during the hatchery period do not predict the success of seeded twine following outplanting.

Ensiling is a promising low-cost preservation approach that allows for a year-round supply of kelp feedstock for biofuel production via anaerobic digestion. In this study, farm-grown kelps of known age were ensiled with and without the addition of lactic acid bacterial (LAB) inoculant for a duration of up to one year in order to test long-term storage suitability. The study looked at the impacts of different bacterial inoculums on the chemical and microbial composition over the duration of storage. Significant fluctuations in the pH were observed during ensiling, leading to some cases of secondary fermentation and a loss of volatile components; however, over 12 months, the total mass loss was <2% on average. Biochemical compositional changes occurred in the silage over a period of 12 months, but protein, lipid and carbohydrate content remained suitable for biogas production. Microbial analysis showed variability in the bacterial distribution between the ensiled samples that was coincident with pH variability. Despite this variability, the bacterial communities underwent a succession with a selection for ensilage bacteria and drop in spoilage organisms. This shift supports the viability of this ensiled material for future usage. The impact of ensiling on bioenergy production through anaerobic digestion is explored in the second part of this two-part paper.

Phaeophyte macroalgae of the genus Sargassum, including Sargassum muticum, are under investigation as a cultivation crop. Overgrowth or grazing reduces the value and productivity of the crop. This can occur both in the hatchery and during growth at sea, although juvenile stages are especially vulnerable. A decontamination protocol could be used to prevent this. Following a screening procedure, sodium hypochlorite (NaClO) and potassium iodide (KI) were selected for further study. The lethal concentrations for protozoans associated with S. muticum zygotes were 1 % KI, 0.75 % NaClO or a combination of 0.5 % KI and 0.38 % NaClO. A 3-min exposure to these treatments was able to eliminate protozoa from branchlets 20–80 % of the time. NaClO caused large reductions in the operating efficiency of photosystem II (Fq ’/Fₘ ’), particularly in juveniles (74 ± 17 %), which had still not fully recovered after 17 days. This also halved juvenile density and caused negative growth. One percent KI reduced Fq ’/Fₘ ’ in adults by 29 ± 11 %, with recovery by day 10. In juveniles, growth was reduced by 65 % and Fq ’/Fₘ ’ by 61 ± 11 % with recovery after 17 days. A combined treatment of 0.5 % KI and 0.38 % NaClO had far milder effects: reducing adult and juveniles Fq ’/Fₘ ’ by 6 ± 3 and 34 ± 9 % respectively, with full recovery by day 10. A reduction in juvenile growth was also seen between day 0–10 (32 %); however, size was no different to the control by day 20. This combined treatment is therefore suitable for decontamination of both juveniles and adult S. muticum tissue.

The phaeophyte macroalga Saccharina latissima is gaining economic importance as an aquaculture crop. To decrease costs associated with the hatchery, the time required for meiospores to develop into sporophytes ready for outplanting must be minimised and survivorship maximised. The settlement and juvenile development of S. latissima was examined in a series of experimental manipulations. It was determined that (1) Meiospore settlement should be conducted in the dark in nutrient-enriched medium. (2) Continued nutrient enrichment in the hatchery increased growth and survival of the developing sporophytes. (3) It is best to use the diatom inhibitor germanium dioxide only during settlement and the first week of light exposure, rather than continuously or not at all. This treatment leads to the highest survival rate and sporophyte length. (4) Pre-treating the settlement surface with a commercial yeast extract can increase settlement and early development size; however, over-application can be highly detrimental leading to reduced survival, size and patchy growth.

The effect of a range of chemical disinfectants at different concentration and exposure times was investigated on five macroalgal species and the marine gastropod Littorina spp. Palmaria palmata , Osmundea pinnatifida and Ulva lactuca are commercially valuable and are often cultivated in tanks for food or feed. Ectocarpus siliculosus and Ulva intestinalis are common epiphytes of P. palmata and O. pinnatifida cultures, whilst Littorina spp. are common herbivorous epibionts within U. lactuca culture tanks. These contaminants reduce the productivity and quality of the culture as a food. Differential tolerance to the treatments was seen between the algal species using pulse-amplitude modulation (PAM) chlorophyll a fluorescence, a few hours and a week following treatment. We identified treatments that selectively damaged the epiphyte but not the basiphyte species. Ectocarpus siliculosus had a significantly lower tolerance to 1 % sodium hypochlorite than P. palmata , and to 25 % methanol than O. pinnatifida , with a 1–5 min exposure appearing most suitable. Ulva intestinalis had a significantly lower tolerance than P. palmata and O. pinnatifida to many disinfectants: 0.1–1 % sodium hypochlorite for 10 min, 0.5 % potassium iodide for up to 10 min, and 0.25 % Kick-start (a commercial aquaculture disinfectant solution) for 1–5 min. No treatment was able to kill the gastropod snails without also damaging U. lactuca , although agitation in freshwater for an hr may cause them to detach from the basiphyte, with little to no photophysiological impact seen to U. lactuca . This experiment forms the basis for more extended commercial trials.

Brown macroalgae are an important source of polysaccharides, mainly fucose-containing sulphated polysaccharides (FCSPs), associated with several biological activities. However, the structural diversity and structure–function relationships for their bioactivities are still undisclosed. Thus, the aim of this work was to characterize the chemical structure of water-soluble Saccharina latissima polysaccharides and evaluate their immunostimulatory and hypocholesterolemic activities, helping to pinpoint a structure–activity relationship. Alginate, laminarans (F1, neutral glucose-rich polysaccharides), and two fractions (F2 and F3) of FCSPs (negatively charged) were studied. Whereas F2 is rich in uronic acids (45 mol%) and fucose (29 mol%), F3 is rich in fucose (59 mol%) and galactose (21 mol%). These two fractions of FCSPs showed immunostimulatory activity on B lymphocytes, which could be associated with the presence of sulphate groups. Only F2 exhibited a significant effect in reductions in in vitro cholesterol’s bioaccessibility attributed to the sequestration of bile salts. Therefore, S. latissima FCSPs were shown to have potential as immunostimulatory and hypocholesterolemic functional ingredients, where their content in uronic acids and sulphation seem to be relevant for the bioactive and healthy properties.