Biochemical composition of red, green and brown seaweeds on the Swedish west coast

Seaweed biomass has the potential to become an important raw material for bio-based production. The aim of this study was to screen the overall composition of several seaweed species on the Swedish west coast, including some scarcely studied species, to provide fundamentals for evaluation of biorefining potential and to benchmark with already potentially industrially relevant species and commercially important land-based biomasses. Twenty-two common seaweed species (green, red, brown) were collected and the carbohydrate, ash, protein, water and metal contents were measured. Carbohydrate content varied between 237 and 557\ua0g\ua0kg−1 dry weight (dw), making it the largest constituent, on a dry weight basis, of most species in the study. Ash, which is considered unwanted in biorefining, ranged between 118 and 419\ua0g\ua0kg−1 dw and was the largest constituent in several seaweeds, which were therefore considered unsuitable for biorefining. Protein content was most abundant in the red seaweeds but was generally low in all species (59–201\ua0g\ua0kg−1 dw). High contents of several unwanted metals for processing or human consumption were found (e.g. aluminium, arsenic, copper, chromium and nickel), which need to be considered when utilizing seaweeds for certain applications. Potential targets for further biorefinery development mostly include species already known for their potential (Saccharina latissima, Laminaria digitata and Chondrus crispus) while some, such as Halidrys siliquosa and Dilsea carnosa, have not been previously noted. However, more detailed studies are required to explore biorefinery processes for these seaweeds, as well as how to potentially cultivate them

Production of protein extracts from Swedish red, green, and brown seaweeds, Porphyra umbilicalis Kützing, Ulva lactuca Linnaeus, and Saccharina latissima (Linnaeus) J. V. Lamouroux using three different methods

peer-reviewedThe demand for vegetable proteins increases globally and seaweeds are considered novel and promising protein sources. However, the tough polysaccharide-rich cell walls and the abundance of polyphenols reduce the extractability and digestibility of seaweed proteins. Therefore, food grade, scalable, and environmentally friendly protein extraction techniques are required. To date, little work has been carried out on developing such methods taking into consideration the structural differences between seaweed species. In this work, three different protein extraction methods were applied to three Swedish seaweeds (Porphyra umbilicalis, Ulva lactuca, and Saccharina latissima). These methods included (I) a traditional method using sonication in water and subsequent ammonium sulfate-induced protein precipitation, (II) the pH-shift protein extraction method using alkaline protein solubilization followed by isoelectric precipitation, and (III) the accelerated solvent extraction (ASE®) method where proteins are extracted after pre-removal of lipids and phlorotannins. The highest protein yields were achieved using the pH-shift method applied to P. umbilicalis (22.6 ± 7.3%) and S. latissima (25.1 ± 0.9%). The traditional method resulted in the greatest protein yield when applied to U. lactuca (19.6 ± 0.8%). However, the protein concentration in the produced extracts was highest for all three species using the pH-shift method (71.0 ± 3.7%, 51.2 ± 2.1%, and 40.7 ± 0.5% for P. umbilicalis, U. lactuca, and S. latissima, respectively). In addition, the pH-shift method was found to concentrate the fatty acids in U. lactuca and S. latissima by 2.2 and 1.6 times, respectively. The pH-shift method can therefore be considered a promising strategy for producing seaweed protein ingredients for use in food and feed

Complex Interactions of Temperature, Light and Tissue Damage on Seagrass Wasting Disease in Zostera marina

The temperate seagrass species eelgrass Zostera marina can be infected by the wasting disease pathogen Labyrinthula zosterae, which is believed to have killed about 90% of the seagrass in the Atlantic Ocean in the 1930s. It is not known why this opportunistic pathogen sometimes becomes virulent, but the recurrent outbreaks may be due to a weakening of the Z. marina plants from adverse environmental changes. This study investigated the individual and interactive effects of multiple extrinsic factors (temperature, light, and tissue damage) on the host-pathogen interaction between Z. marina and L. zosterae in a fully crossed infection experiment. The degree of infection was measured as both lesion coverage and L. zosterae cell concentration. We also investigated if the treatment factors affect the chemical defense of the host, measured as the inhibitory capacity of seagrass extracts in bioassays with L. zosterae. Finally, gene expression of a set of targeted genes was quantified in order to investigate how the treatments change Z. marina’s response to infection. Light had a pronounced effect on L. zosterae infection measured as lesion coverage, where reduced light conditions increased lesions by 35%. The response to light on L. zosterae cell concentration was more complex and showed significant interaction with the temperature treatment. Cell concentration was also significantly affected by physical damage, where damage surprisingly resulted in a reduced cell concentration of the pathogen. No treatment factor caused detectable decrease in the inhibitory capacity of the seagrass extracts. There were several interactive effects between L. zosterae infection and the treatment factors on Z. marina growth, and on the expression of genes associated with immune defense, phenol synthesis and primary metabolism, showing that the molecular reaction toward L. zosterae infection depends on prevailing environmental conditions. Our study shows that individual or interactive effects of light, temperature and tissue damage can affect multiple aspects of host-pathogen interactions in seagrasses. These results highlight the complexity of marine host-pathogen systems, showing that more multi-factorial investigations are needed to gain a better understanding of disease in marine plants under different environmental conditions

Seagrass wasting disease varies with salinity and depth in natural Zostera marina populations

In the 1930s the wasting disease pathogen Labyrinthula zosterae is believed to have killed 90% of the temperate seagrass Zostera marina in the Atlantic Ocean. Despite the devastating impact of this disease the host–pathogen interaction is still poorly understood, and few field studies have investigated factors correlating with the prevalence and abundance of L. zosterae. This study measures wasting disease in natural populations of Z. marina, showing a strong correlation between the disease and both salinity and water depth. No infection was detected in Z. marina shoots from low salinity (13–25 PSU) meadows, whereas most shoots carried the disease in high salinity (25–29 PSU). Shallow (1 m) living Z. marina shoots were also more infected compared to shoots in deeper (5 m) meadows. In addition, infection and transplantation experiments showed that Z. marina shoots from low salinity meadows with low pathogen pressure were more susceptible to L. zosterae infection. The higher susceptibility could not be explained by lower content of inhibitory defense compounds in the shoots. Instead, extracts from all Z. marina shoots significantly reduced pathogen growth, suggesting that Z. marina contains inhibitory compounds that function as a constitutive defense. Overall, the results show that seagrass wasting disease is common in natural Z. marina populations in the study area and that it increases with salinity and decreases with depth. Our findings also suggest that low salinity areas can act as a refuge against seagrass wasting disease

Closed life-cycle aquaculture of sea lettuce (Ulva fenestrata): performance and biochemical profile differ in early developmental stages

Sea lettuce (Ulva) aquaculture has increased the last decade due to high productivity, wide environmental tolerance, and interesting functional and nutritional properties of the crop. Research focus has mainly been on adult biomass production, but knowledge of performance and biochemical content of early developmental stages – which are the basis to any large-scale production - is still limited. The life-history of Ulva alternates between a diploid sporophytic life-stage and a haplontic gametophytic life-stage. Whereas the sporophyte give raise to recombinant gametophytes through zoids, gametophytes can give raise to parthenogenetically developing, clonal gametes in absence of a mating partner. This study shows that recombinant gametophytes have a faster ontogenetic development, higher growth rate, as well as higher protein, fatty acid, and pigment contents compared to clonal gametophytes of the crop Ulva fenestrata. Nutrient addition is required for a normal development, but temperature and swarmer density have relatively small effects on the hatchery success, relative growth rate and biochemical profile of the juvenile biomass. Our study reveals that the selection of the life-history-phase in novel sea lettuce crop strains could largely contribute to the emerging seaweed aquaculture sector

Effect of storage conditions on lipid oxidation, nutrient loss and colour of dried seaweeds, Porphyra umbilicalis and Ulva fenestrata, subjected to different pretreatments

Here we evaluated the levels of lipid oxidation products, fatty acids, ascorbic acid and colour of Porphyra and Ulva after oven-drying at 40 \ub0C, and during subsequent storage for ≥370 days under light, semi-light and dark conditions. Part of the seaweed was pre-soaked in freshwater or pre-coated with a whey protein mixture. Controls consisted of freeze-dried seaweeds. Throughout storage there was a moderate development of the lipid oxidation-derived aldehydes, malondialdehyde, 4-hydroxy-trans-2-hexenal and 4-hydroxy-trans-2-nonenal, while there was a great loss of unsaturated fatty acids and ascorbic acid. Light storage and freeze-drying stimulated the fatty acid loss as well as pigment bleaching, seen as increased a*-values. For Ulva, the coating reduced malondialdehyde, 4-hydroxy-trans-2-hexenal and 4-hydroxy-trans-2-nonenal formation during drying and slightly prevented loss of polyunsaturated fatty acids during light storage. Pre-soaking in freshwater had no effect on the seaweed stability, although it reduced the ash content and thereby increased the relative content of ascorbic acid and fatty acids of the biomasses

Post-harvest cultivation with seafood process waters improves protein levels of Ulva fenestrata while retaining important food sensory attributes

Seaweed aquaculture can provide the growing human population with a sustainable source of proteins. Sea-based cultivation is an effective method for farming seaweeds on a large scale and can yield high biomass output. However, the quality and biochemical composition of the biomass is seasonally dependent, which limits the harvests to certain periods of the year. Here we show the possibility to extend the sea-based cultivation season of Ulva fenestrata when aiming for high protein levels, by post-harvest treatment in herring production process waters. We harvested U. fenestrata at an optimal period in terms of yield, but suboptimal in terms of protein content. We then cultivated the seaweed in onshore tank systems with the nutrient-rich process waters for 14 days. We monitored biomass yield, crude protein content, amino acid composition, and content of the health concerning metals arsenic, mercury, lead, and cadmium, as well as the sensory properties of the dried biomass. After cultivation in the process waters, biomass yields were 30 - 40% higher (210 – 230 g fresh weight) compared to in seawater (160 g fresh weight). Also, the crude protein and amino acid content increased three to five times in the process waters, reaching 12 - 17 and 15 – 21% dry weight, respectively. The protein enriched biomass followed food graded standards for heavy metal content, and consumption of the biomass does not exceed health based reference points. Additionally, no sensory attributes regarded as negative were found. This rapid, post-harvest treatment can help extend the cultivation season of sea-based seaweed farms, maximizing their output of sustainable proteins

Sustainable large-scale aquaculture of the northern hemisphere sea lettuce, ulva fenestrata, in an off-shore seafarm

The growing world population demands an increase in sustainable resources for biorefining. The opening of new farm grounds and the cultivation of extractive species, such as marine seaweeds, increases worldwide, aiming to provide renewable biomass for food and non-food applications. The potential for European large-scale open ocean farming of the commercial green seaweed crop Ulva is not yet fully realized. Here we conducted manipulative cultivation experiments in order to investigate the effects of hatchery temperature (10 and 15◦C), nutrient addition (PES and 3xPES) and swarmer density (500 and 10,000 swarmers ml−1 ) on the biomass yield and biochemical composition (fatty acid, protein, carbohydrate, pigment and phenolic content) of off-shore cultivated Ulva fenestrata in a Swedish seafarm. High seedling densities were optimal for the growth of this northern hemisphere crop strain and significantly increased the mean biomass yield by ~84% compared to low seedling densities. Variations of nutrients or changes in temperature levels during the hatchery phase were not necessary to increase the subsequent growth in an open-water seafarm, however effects of the factors on the thallus habitus (thallus length/width) were observed. We found no significant effect of the environmental factors applied in the hatchery on the total fatty acid or crude protein content in the off-shore cultivated Ulva. However, low seedling density and low temperature increased the total carbohydrate content and furthermore, high temperature in combination with high nutrient levels decreased the pigment content (chlorophyll a, b, carotenoids). Low temperature in combination with high nutrient levels increased the phenolic content. Our study confirms the successful and sustainable potential for large-scale off-shore cultivation of the Scandinavian crop U. fenestrata. We conclude that high seedling density in the hatchery is most important for increasing the total biomass yield of sea-farmed U. fenestrata, and that changing temperature or addition of nutrients overall does not have a large effect on the biochemical composition. To summarize, our study contributes novel insights into the large-scale off-shore cultivation potential of northern hemisphere U. fenestrata and underpins suitable pre-treatments during the hatchery phase of seedlings to facilitate a successful and cost-efficient large-scale rope cultivation

In vitro digestibility and Caco-2 cell bioavailability of sea lettuce (Ulva fenestrata) proteins extracted using pH-shift processing

Seaweed is a promising sustainable source of vegan protein as its farming does not require arable land, pesticides/insecticides, nor freshwater supply. However, to be explored as a novel protein source the content and nutritional quality of protein in seaweed need to be improved. We assessed the influence of pH-shift processing on protein degree of hydrolysis (%DH), protein/peptide size distribution, accessibility, and cell bioavailability of Ulva fenestrata proteins after in vitro gastrointestinal digestion. pH-shift processing of Ulva, which concentrated its proteins 3.5-times, significantly improved the %DH from 27.7\ub12.6% to 35.7\ub12.1% and the amino acid accessibility from 56.9\ub14.1% to 72.7\ub10.6%. Due to the higher amino acid accessibility, the amount of most amino acids transported across the cell monolayers was higher in the protein extracts. Regarding bioavailability, both Ulva and protein extracts were as bioavailable as casein. The protein/peptide molecular size distribution after digestion did not disclose a clear association with bioavailability