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Sustainable Seaweed Biotechnology Solutions for Carbon Capture, Composition, and Deconstruction

2020; Elsevier BV; Volume: 38; Issue: 11 Linguagem: Inglês

10.1016/j.tibtech.2020.03.015

0167-9430

Lieve M. L. Laurens, Madeline Lane, Robert S. Nelson,

Food Industry and Aquatic Biology

A realistic framework around seaweed carbon capture potential and seaweed biomass conversion is needed to guide future bioenergy production.Maximizing carbon storage in the biomass based on marine agronomy in the underutilized exclusive economic zone of the oceans represents significant untapped resources.Using biotechnological applications for deconstruction of the famously complex polysaccharides provides a route towards the discovery of new enzymatic cascades present in microbial communities.Seaweed-based industrial biotechnology allows for exploitation of the intrinsic biomass value based on its biochemical composition.It is necessary to place the seaweed biorefinery discussion in the context of the large-scale, offshore farms that are envisioned for bioenergy production to create market opportunities commensurate with the volumes produced. Seaweeds or macroalgae are attractive candidates for carbon capture, while also supplying a sustainable photosynthetic bioenergy feedstock, thanks to their cultivation potential in offshore marine farms. Seaweed cultivation requires minimal external nutrient requirements and allows for year-round production of biomass. Despite this potential, there remain significant challenges associated with realizing large-scale, sustainable agronomics, as well as in the development of an efficient biomass deconstruction and conversion platform to fuels and products. Recent biotechnology progress in the identification of enzymatic deconstruction pathways, tailored to complex polymers in seaweeds, opens up opportunities for more complete utilization of seaweed biomass components. Effective, scalable, and economically viable conversion processes tailored to seaweed are discussed and gaps are identified for yield and efficiency improvements. Seaweeds or macroalgae are attractive candidates for carbon capture, while also supplying a sustainable photosynthetic bioenergy feedstock, thanks to their cultivation potential in offshore marine farms. Seaweed cultivation requires minimal external nutrient requirements and allows for year-round production of biomass. Despite this potential, there remain significant challenges associated with realizing large-scale, sustainable agronomics, as well as in the development of an efficient biomass deconstruction and conversion platform to fuels and products. Recent biotechnology progress in the identification of enzymatic deconstruction pathways, tailored to complex polymers in seaweeds, opens up opportunities for more complete utilization of seaweed biomass components. Effective, scalable, and economically viable conversion processes tailored to seaweed are discussed and gaps are identified for yield and efficiency improvements. The landscape of future sustainable biobased fuels and products will likely rely on a portfolio of different feedstock sources to meet the growing demand for replacements for petroleum-derived fuels and products [1.Laurens L.M.L. et al.Development of algae biorefinery concepts for biofuels and bioproducts; a perspective on process-compatible products and their impact on cost-reduction.Energy Environ. Sci. 2017; 10: 1716-1738Crossref Google Scholar, 2.Chen H. et al.Macroalgae for biofuels production: progress and perspectives.Renew. Sust. Energ. Rev. 2015; 47: 427-437Crossref Scopus (198) Google Scholar, 3.Van Hal J.W. et al.Opportunities and challenges for seaweed in the biobased economy.Trends Biotechnol. 2014; 32: 231-233Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar]. One of the promising emerging sources in this area is biomass derived from seaweed (or macroalgae). Macroalgae are capable of producing more biomass per acre in offshore marine farms compared with their terrestrial crop counterparts and can be sustainably harvested and produced without utilizing valuable arable land or unsustainable nutrient requirements [4.Troell M. et al.Does aquaculture add resilience to the global food system?.Proc. Natl. Acad. Sci. U. S. A. 2014; 111: 13257-13263Crossref PubMed Scopus (349) Google Scholar, 5.Buschmann A.H. et al.Seaweed production: overview of the global state of exploitation, farming and emerging research activity.Eur. J. Phycol. 2017; 52: 391-406Crossref Scopus (267) Google Scholar, 6.Hafting J.T. et al.Prospects and challenges for industrial production of seaweed bioactives.J. Phycol. 2015; 51: 821-837Crossref PubMed Scopus (135) Google Scholar, 7.Fernand F. et al.Offshore macroalgae biomass for bioenergy production: environmental aspects, technological achievements and challenges.Renew. Sust. Energ. Rev. 2017; 75: 35-45Crossref Scopus (102) Google Scholar, 8.Camus C. et al.Overview of 3 year precommercial seafarming of Macrocystis pyrifera along the Chilean coast.Rev. Aquacult. 2018; 10: 543-559Crossref Scopus (30) Google Scholar, 9.Troell M. et al.Ecological engineering in aquaculture: use of seaweeds for removing nutrients from intensive mariculture.J. Appl. Phycol. 1999; 11: 89-97Crossref Scopus (149) Google Scholar]. In particular, the topical emergence of seaweed in algal blooms occurring around the world has the bioenergy community focused on developing solutions to harvest and then maximize the conversion and recovery of the biochemicals entrained in the biomass. Similar to microalgae, the biomass conversion process for seaweeds is modeled as a biorefinery and necessitates a discussion around biomass composition, intrinsic value of the components, and, ultimately, conversion to products as a success metric [1.Laurens L.M.L. et al.Development of algae biorefinery concepts for biofuels and bioproducts; a perspective on process-compatible products and their impact on cost-reduction.Energy Environ. Sci. 2017; 10: 1716-1738Crossref Google Scholar]. Despite this potential, there are significant challenges associated with realizing both the cultivation and harvesting logistics, as well as in developing an efficient biomass deconstruction and conversion platform to fuels and products. Effective, scalable, and economically viable conversion processes tailored to seaweeds are discussed in detail and gaps are identified that outline the needs for yield and efficiency improvements. In particular, the recent interest and multiyear, multimillion dollar investment of the Department of Energy's Advanced Research Projects Agency-Energy supports a shift in both government and industry interest (https://arpa-e.energy.gov/?q=arpa-e-programs/mariner). The concept of developing a biorefinery approach to maximize the value derived from seaweed biomass is represented in the literature but is often not placed in the context of sustainable bioproducts and bioenergy productions. Often, literature reports relate to the ongoing challenges with respect to carbon capture potential in an agronomic setting that does not compete within a food versus fuel debate. With the discussion here, we aim to drive the narrative to a more realistic framework around seaweed carbon capture and bioenergy conversion. This review will be focused around the following topics: carbon storage in the biomass and carbon capture potential based on the underutilized exclusive economic zone (EEZ) of the oceans that represent ideal marine agriculture locations; application of biotechnological applications towards deconstruction of the complex biomass composition, including the discovery of new enzyme cascades present in microbial communities; consideration of seaweed intrinsic biomass value based on composition and the challenges associated with in-depth characterization of macroalgae; and placing the biorefinery discussion in the context of the large-scale, offshore farms that are envisioned for bioenergy production and thus create market opportunities commensurate with the volumes produced. In the context of supplying a feedstock for bioenergy applications, the primary consideration is the scale of production capacity. It is estimated that current global marine agronomy is able to produce around 30 MMT (million metric, dry, tonnes) of seaweed per year, of which production in the USA is estimated to be around 425 000 T [10.Food and Agriculture Organization (FOA) of the United Nations The State of World Fisheries and Aquaculture. FOA, 2016Google Scholar,11.LiVecchi A. et al.Powering the Blue Economy; Exploring Opportunities for Marine Renewable Energy in Maritime Markets. US Department of Energy, 2019Google Scholar]. Of this, 29.4 MMT was cultivated in a marine agriculture setting and produced and 1.1 MMT was harvested in the wild. The primary driver for this production is to support the growing global markets in seaweed-derived hydrocolloid polymers and other high-value products for food, feed, and agriculture application [12.Porse H. Rudolph B. The seaweed hydrocolloid industry: 2016 updates, requirements, and outlook.J. Appl. Phycol. 2017; 29: 2187Crossref Scopus (152) Google Scholar]. Almost all of this production is driven by a couple of species: Kappaphycus alvarezii, Eucheuma spp., Laminaria spp., Gracilaria spp., Undaria pinnatifida, Porphyra spp. (some species in this genus were renamed as Pyropia spp., a.k.a. nori), Sargassum fusiforme, and Ulva spp. in global production [10.Food and Agriculture Organization (FOA) of the United Nations The State of World Fisheries and Aquaculture. FOA, 2016Google Scholar,12.Porse H. Rudolph B. The seaweed hydrocolloid industry: 2016 updates, requirements, and outlook.J. Appl. Phycol. 2017; 29: 2187Crossref Scopus (152) Google Scholar, 13.Froehlich H.E. et al.Blue growth potential to mitigate climate change through seaweed offsetting.Curr. Biol. 2019; 29: 1-7Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar, 14.Hwang E.K. et al.Seaweed breeding programs and progress in eastern Asian countries.Phycologia. 2019; 58: 484-495Crossref Scopus (46) Google Scholar]. Most recently, there is an additional and growing interest in harvesting fast-growing seaweeds that are entrapped in natural algae blooms for conversion to bioenergy. The unpredictability of algal blooms may present challenges in a bioenergy supply chain, however, it is a source that is currently not utilized and may become a supplemental source of biomass [15.Pandey M.K. et al.Bioprospecting microalgae from natural algal bloom for sustainable biomass and biodiesel production.Appl. Microbiol. Biotechnol. 2019; 103: 5447-5458Crossref PubMed Scopus (13) Google Scholar]. When comparing the current production levels with the total entrained energy potential of seaweed, there is potential for seaweed to displace a significant burden on imported energy and thus contribute to the global carbon capture and utilization solution. In particular, the EEZ of the USA represents a significant portion that could be used for aquaculture and marine agronomic development (Figure 1). In the context of the large marine ecosystems approach to preserve and restore the natural ecosystems around the world, there are tremendous opportunities to develop a sustainable macroalgae-based aquaculture. The value that macroalgae provide to global geochemical cycling (among other benefits) includes a carbon and excess nutrient-capture approach. Especially in the Gulf of Mexico, macroalgae opportunities exist and address the needed nutrient cycling that is rapidly becoming a priority for ocean and coastal management [16.Duffy J.E. et al.Toward a coordinated global observing system for seagrasses and marine macroalgae.Front. Mar. Sci. 2019; 6: 317Crossref Scopus (73) Google Scholar]. Similarly, offshore large-scale integrated multitrophic aquaculture is a promising route to support aquaculture in combination with effective biofiltration of excess nutrients [17.Troell M. et al.Ecological engineering in aquaculture - potential for integrated multi-trophic aquaculture (IMTA) in marine offshore systems.Aquaculture. 2009; 297: 1-9Crossref Scopus (344) Google Scholar]. If only a fraction (~2.5%) of the EEZ (250 000 km2) could be used for deploying a national marine agriculture program, estimated (future) yields of between 300 and 1120 million tons of seaweed can be achieved [5.Buschmann A.H. et al.Seaweed production: overview of the global state of exploitation, farming and emerging research activity.Eur. J. Phycol. 2017; 52: 391-406Crossref Scopus (267) Google Scholar,13.Froehlich H.E. et al.Blue growth potential to mitigate climate change through seaweed offsetting.Curr. Biol. 2019; 29: 1-7Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar,18.Bruhn A. et al.Bioenergy potential of Ulva lactuca: biomass yield, methane production and combustion.Bioresour. Technol. 2011; 102: 2595-2604Crossref PubMed Scopus (298) Google Scholar]. Assuming an effective conversion process is available to convert at least half of the energy entrained in the harvested macroalgal biomass (with an assumed caloric content of 14 MJ kg–1 ), to for example biogas, between 10% and 20% of the 31 Quad BTU (equivalent to approximately 31 exajoules, EJ) imported fossil energy natural gas used in the USA in 2018 (https://www.eia.gov/energyexplained/us-energy-facts/) could be displaced. Similarly, if an efficient, high yielding, biofuel conversion process is found, a similar fraction of the imported petroleum (36 Quad BTU, or 36 EJ) can be displaced. These values correspond to just over 200 million tons of CO2 [19.Duarte C.M. et al.Can seaweed farming play a role in climate change mitigation and adaptation?.Front. Mar. Sci. 2017; 4: 100Crossref Scopus (201) Google Scholar,20.Aitken D. et al.Life cycle assessment of macroalgae cultivation and processing for biofuel production.J. Clean. Prod. 2014; 75: 45-56Crossref Scopus (113) Google Scholar]. Since much of the EEZ is currently underutilized, a fraction of this area could be developed for marine bioenergy applications, while respecting competing uses for ocean resources [21.Roesijadi G. et al.Macroalgae Analysis. US Department of Energy, 2011Google Scholar]. The carbon capture potential of cultivated seaweed at least matches and often exceeds that of terrestrial farmed crops, with minimally intensive agricultural practices and nutrient requirements. Seaweed biomass productivities of between 1450 and 14 000 T volatile solids (VS, or ash-free dry weight) km–2 year–1 have been reported, corresponding to between 6 and 57 dry T acre–1 year–1, depending on species and growth environment, that is, wild harvest or (intensively) cultivated (Table 1) [5.Buschmann A.H. et al.Seaweed production: overview of the global state of exploitation, farming and emerging research activity.Eur. J. Phycol. 2017; 52: 391-406Crossref Scopus (267) Google Scholar,13.Froehlich H.E. et al.Blue growth potential to mitigate climate change through seaweed offsetting.Curr. Biol. 2019; 29: 1-7Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar,18.Bruhn A. et al.Bioenergy potential of Ulva lactuca: biomass yield, methane production and combustion.Bioresour. Technol. 2011; 102: 2595-2604Crossref PubMed Scopus (298) Google Scholar,20.Aitken D. et al.Life cycle assessment of macroalgae cultivation and processing for biofuel production.J. Clean. Prod. 2014; 75: 45-56Crossref Scopus (113) Google Scholar,22.Buck B.H. Buchholz C.M. The offshore-ring: a new system design for the open ocean aquaculture of macroalgae.J. Appl. Phycol. 2004; 16: 355-368Crossref Scopus (124) Google Scholar,23.Gao K. McKinley K.R. Use of macroalgae for marine biomass production and CO2 remediation: a review.J. Appl. Phycol. 1994; 6: 45-60Crossref Scopus (267) Google Scholar]. This compares against 40 fresh T acre–1 year–1 for sugar cane as the representative highest yielding terrestrial crop (yielding 5 T sugar acre–1 year–1) (USDA, ERS, 2019 figures, www.ers.usda.gov/media/8310/table15.xls). Because of the order of magnitude reported range in seaweed productivity, it is hard to estimate the derivative data on carbon capture potential of seaweed. For carbon capture calculations, we have assumed a 30% carbon content on a dry weight basis, comparable with measured and representative carbon in wild-harvested Ulva, Sargassum, and Gracilaria 27–32%, or 37–45% on a VS basis (Box 1). For the purpose of this review, it is important to remain cognizant of both the seaweed production potential as well as the variation in carbon content, which, when both are optimized, can have a positive impact on overall carbon capture potential of the future marine agronomy.Table 1Summary of Reported Seaweed Biomass Productivity Potential and Associated CO2 CaptureSpeciesBiomassT VS km–2 year–1(T VS acre–1 year–1)aData collected across literature reports and normalized based on areal productivity, all assuming a 30% carbon content on the basis of volatile solids (VS), or ash-free dry weight; ND refers to an undefined seaweed species and an average (conservative) value of biomass productivity [13].Biomass(g VS m–2 day–1)CarbonT km–2 year–1(30% C)CO2 captureT km–2 year–1(T acre–1 year–1)RefsND1450 (6)4.04351595 (6)[13.Froehlich H.E. et al.Blue growth potential to mitigate climate change through seaweed offsetting.Curr. Biol. 2019; 29: 1-7Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar]Macrocystis pyrifera1800 (7)4.95401980 (8)[24.Buschmann A.H. et al.Seaweed future cultivation in Chile: perspectives and challenges.Int. J. Environ. Pollut. 2008; 33: 432-456Crossref Scopus (58) Google Scholar]M. pyrifera2000 (8)5.56002200 (9)[5.Buschmann A.H. et al.Seaweed production: overview of the global state of exploitation, farming and emerging research activity.Eur. J. Phycol. 2017; 52: 391-406Crossref Scopus (267) Google Scholar,13.Froehlich H.E. et al.Blue growth potential to mitigate climate change through seaweed offsetting.Curr. Biol. 2019; 29: 1-7Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar]Ulva lactuca4500 (18)12.313504950 (20)[18.Bruhn A. et al.Bioenergy potential of Ulva lactuca: biomass yield, methane production and combustion.Bioresour. Technol. 2011; 102: 2595-2604Crossref PubMed Scopus (298) Google Scholar]Laminaria longicruris7407 (30)20.322228149 (33)[23.Gao K. McKinley K.R. Use of macroalgae for marine biomass production and CO2 remediation: a review.J. Appl. Phycol. 1994; 6: 45-60Crossref Scopus (267) Google Scholar]Gracilaria chilensis14 000 (57)38.4420015 400 (62)[20.Aitken D. et al.Life cycle assessment of macroalgae cultivation and processing for biofuel production.J. Clean. Prod. 2014; 75: 45-56Crossref Scopus (113) Google Scholar]a Data collected across literature reports and normalized based on areal productivity, all assuming a 30% carbon content on the basis of volatile solids (VS), or ash-free dry weight; ND refers to an undefined seaweed species and an average (conservative) value of biomass productivity [13.Froehlich H.E. et al.Blue growth potential to mitigate climate change through seaweed offsetting.Curr. Biol. 2019; 29: 1-7Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar]. Open table in a new tab Box 1Compositional Profile of Major Seaweed RepresentativesDistinct biomass compositional profiles are associated with each of three representative seaweed species, Ulva fasciata, Gracilaria parvispora, and Sargassum echinocarpum (Table I). These three genera are of interest in current research on conversion to bioenergy products and their respective biomass composition is described in detail here. Consistently, about a third of the biomass is entrained in ash, with the majority of the rest of the measured biomass composition found in the carbohydrate fraction, which reaches around 40% of the ash-free portion of the biomass, and is likely higher due to the incomplete measurement of all monosaccharides that make up the complex polymeric structures. On an ash-free or volatile solids (VS) basis, the biomass carbon content reaches up to 45% for Sargassum, consistent with the high observed carbohydrate content.When looking at the molecular make-up of the monosaccharides that comprise the carbohydrate fraction (Table II), there are distinct sugars that can be found in the hydrolyzed liquors from each of the species. In the case of Ulva, the primary monosaccharides are glucose, rhamnose, and uronic acids, consistent with published reports on the presence of cellulose in green algae [76.Popper Z.A. et al.Evolution and diversity of plant cell walls: from algae to flowering plants.Annu. Rev. Plant Biol. 2011; 62: 567-590Crossref PubMed Scopus (459) Google Scholar], while for Gracilaria it is galactose (most likely derived from the agar polymers) and glucose, and for Sargassum primary components are the uronic acids and glucose. Such different compositional structures will undoubtedly require adaptation of a selective fermentation approach [64.Enquist-Newman M. et al.Efficient ethanol production from brown macroalgae sugars by a synthetic yeast platform.Nature. 2014; 505: 239-243Crossref PubMed Scopus (239) Google Scholar].The lipid content, reported as the sum of the fatty acids after in situ transesterification [77.Laurens L. et al.Accurate and reliable quantification of total microalgal fuel potential as fatty acid methyl esters by in situ transesterification.Anal. Bioanal. Chem. 2012; 403: 167-178Crossref PubMed Scopus (171) Google Scholar] is shown in Table I, while the fatty acids that make up the lipids before and after washing the biomass upon wild harvest are shown in Table III. In Table III, all data are expressed on a total fatty acid methyl ester (FAME) basis, reported on an ash-free dry basis (i.e., VS) after lyophilization of the biomass. All fatty acids are presented by their [carbon number]:[number of unsaturated bonds along the carbon chain]; C11CP and C13CP refer to the cyclopentyl dihydrochaulmoogric and dihydrohydnocarpic acids, respectively, as previously identified [78.Aknin M. et al.Sterol and fatty acid distribution in red algae from the Senegalese coast.Comp. Biochem. Physiol. Part B Biochem. 1990; 96: 559-563Crossref Scopus (22) Google Scholar,79.Miralles J. et al.Cyclopentyl and ω-5 monounsaturated fatty acids from red algae of the Solieriaceae.Phytochemistry. 1990; 29: 2161-2163Crossref Scopus (21) Google Scholar] and quantified by gas chromatography after in situ transesterification [77.Laurens L. et al.Accurate and reliable quantification of total microalgal fuel potential as fatty acid methyl esters by in situ transesterification.Anal. Bioanal. Chem. 2012; 403: 167-178Crossref PubMed Scopus (171) Google Scholar,80.Van Wychen S. Laurens L.M.L. Determination of Total Lipids as Fatty Acid Methyl Esters ( FAME ) by in Situ Transesterification - Laboratory Analytical Procedure (LAP). National Renewable Energy Laboratory, 2013Google Scholar].A fatty acid diversity and specificity was observed here that is consistent with the higher unsaturated fatty acids that make up algae lipids [29.Lang I. et al.Fatty acid profiles and their distribution patterns in microalgae: a comprehensive analysis of more than 2000 strains from the SAG culture collection.BMC Plant Biol. 2011; 11: 124Crossref PubMed Scopus (294) Google Scholar]. In particular, omega-3 polyunsaturated fatty acids (e.g., eicosapentaenoic acid, C20:5n3) were detected, albeit at very low concentrations of the biomass, in Gracilaria and Sargassum, potentially opening opportunities for high-value product extraction. Because the analytical methodology is based on a direct, or in situ, transesterification of the whole biomass, data on the origin of the fatty acids (i.e., which intact lipid the fatty acids were associated with) is not available. Cyclopentyl dihydrochaulmoogric and dihydrohydnocarpic acids, unusual metabolite fatty acids, have been detected in Gracilaria; these function as intercellular metabolites and 'local hormones', in particular in the red algae family [78.Aknin M. et al.Sterol and fatty acid distribution in red algae from the Senegalese coast.Comp. Biochem. Physiol. Part B Biochem. 1990; 96: 559-563Crossref Scopus (22) Google Scholar,79.Miralles J. et al.Cyclopentyl and ω-5 monounsaturated fatty acids from red algae of the Solieriaceae.Phytochemistry. 1990; 29: 2161-2163Crossref Scopus (21) Google Scholar]. The proposed identity of the fatty acid derivatives is based on electron impact fragmentation data by gas chromatography mass spectrometry for the two different products; their respective quantification is based on a similar size fatty acid standard, indicating that both together account for almost 15% of the total fatty acids and should not be dismissed as lipid contributors. Because of their so far unknown biological activity, their impact on a biological conversion process could be significant.Table IOverview of Macro-Elemental and Biochemical Composition of Three Seaweed Species, Ulva fasciata, Gracilaria parvispora, and Sargassum echinocarpumAsh(% DW)aAll data are expressed on either a dry basis (%DW) or an ash-free dry basis (i.e., volatile solids, %VS) after lyophilization of the biomass upon wild harvest off the coast of Kailua Kona, Hawaii in June 2019.C(% VS)H(% VS)N(% VS)Lipids (as FAME)bFAME, fatty acid methyl ester after direct transesterification of whole biomass, protein, and carbohydrates, measured as described in [43,73–75].(% VS)Protein(% VS)Carbohydrates (% VS)Ulva fasciata28.5738.26.72.91.5513.9242.8Gracilaria parvispora33.9141.66.53.63.3517.3238.67Sargassum echinocarpum27.3845.16.31.82.788.8238.26a All data are expressed on either a dry basis (%DW) or an ash-free dry basis (i.e., volatile solids, %VS) after lyophilization of the biomass upon wild harvest off the coast of Kailua Kona, Hawaii in June 2019.b FAME, fatty acid methyl ester after direct transesterification of whole biomass, protein, and carbohydrates, measured as described in [43.W.J.J. Huijgen, et al. Determination of carbohydrate composition of macroalgae. In Protocols for Macroalgae Research (Charrier, B. et al., eds.), pp. 199–210, CRC Press, Taylor & FrancisGoogle Scholar,73.Van Wychen S. Laurens L.M.L. Determination of Total Carbohydrates in Algal Biomass - Laboratory Analytical Procedure (LAP). National Renewable Energy Laboratory, 2013Google Scholar, 74.Laurens L.M.L. et al.Harmonization of experimental approach and data collection to streamline analysis of biomass composition from algae in an inter-laboratory setting.Algal Res. 2017; 25: 549-557Crossref Scopus (11) Google Scholar, 75.C. Safi, et al. Quantification of proteins in seaweeds. In Protocols for Macroalgae Research (1st edn) (Charrier, B. et al., eds.), pp. 211–221, CRC Press, Taylor & FrancisGoogle Scholar]. Open table in a new tab Table IIOverview of Biomass Monosaccharide Composition for Three Seaweed Species, Ulva fasciata, Gracilaria parvispora, and Sargassum echinocarpumFucoseaAll data are expressed on an ash-free dry basis (i.e., volatile solids) after lyophilization of the biomass and sulfuric acid hydrolysis, followed by anion exchange chromatography quantification [43,44]. Arabinose and ribose were not detected in any of the seaweed samples.RhamnoseGalactoseGlucoseMannoseXyloseMannitolUronic acidsUlva011.30.4616.0204.63010.39Gracilaria0023.7912.660.660.8800.69Sargassum3.9601.7910.271.090.575.0415.54a All data are expressed on an ash-free dry basis (i.e., volatile solids) after lyophilization of the biomass and sulfuric acid hydrolysis, followed by anion exchange chromatography quantification [43.W.J.J. Huijgen, et al. Determination of carbohydrate composition of macroalgae. In Protocols for Macroalgae Research (Charrier, B. et al., eds.), pp. 199–210, CRC Press, Taylor & FrancisGoogle Scholar,44.Templeton D. et al.Separation and quantification of microalgal carbohydrates.J. Chromatogr. A. 2012; 1270: 225-234Crossref PubMed Scopus (124) Google Scholar]. Arabinose and ribose were not detected in any of the seaweed samples. Open table in a new tab Table IIIOverview Biomass Lipid (Fatty Acid) Composition for Three Seaweed Species, Ulva fasciata, Gracilaria parvispora, and Sargassum echinocarpumC14:0C16:0C16:1n7C18:0C18:1n9C18:1n7C18:2n6C18:3n3C18:4n3C20:3n6C20:4n6C20:5n3C22:0C22:1n9C11CPC13CPUlva0.862.21.61.02.110.53.74.61.40.00.00.04.20.40.00.0Gracilaria0.738.40.40.72.41.10.30.00.01.518.012.90.00.111.32.6Sargassum4.536.02.90.913.30.34.06.66.40.814.34.40.70.20.00.0 Open table in a new tab Distinct biomass compositional profiles are associated with each of three representative seaweed species, Ulva fasciata, Gracilaria parvispora, and Sargassum echinocarpum (Table I). These three genera are of interest in current research on conversion to bioenergy products and their respective biomass composition is described in detail here. Consistently, about a third of the biomass is entrained in ash, with the majority of the rest of the measured biomass composition found in the carbohydrate fraction, which reaches around 40% of the ash-free portion of the biomass, and is likely higher due to the incomplete measurement of all monosaccharides that make up the complex polymeric structures. On an ash-free or volatile solids (VS) basis, the biomass carbon content reaches up to 45% for Sargassum, consistent with the high observed carbohydrate content. When looking at the molecular make-up of the monosaccharides that comprise the carbohydrate fraction (Table II), there are distinct sugars that can be found in the hydrolyzed liquors from each of the species. In the case of Ulva, the primary monosaccharides are glucose, rhamnose, and uronic acids, consistent with published reports on the presence of cellulose in green algae [76.Popper Z.A. et al.Evolution and diversity of plant cell walls: from algae to flowering plants.Annu. Rev. Plant Biol. 2011; 62: 567-590Crossref PubMed Scopus (459) Goo