Innovative processing strategies and technologies to obtain hydrocolloids from macroalgae for food applications

Characterization and Gelling Potential of Macroalgae Extracts Obtained Through Eco-Friendly Technologies for Food-Grade Gelled Matrices

The growing demand for sustainable and nutrient-rich food sources has positioned macroalgae as a promising alternative for food product development. This study investigates the extraction and characterization of hydrocolloids from three red macroalgae species (Chondrus crispus, Gracilaria gracilis, and Gelidium corneum) using water bath (WB), ultrasound (US), and hybrid ultrasound-water bath (USWB) treatments for 45 and 60 min. The physicochemical properties of the extracts, including rheological behavior, particle size distribution, antioxidant activity, and texture, were assessed. The results show that C. crispus produced the firmest gels due to its high carrageenan content, with WB and USWB treatments yielding the most stable gel structures. In contrast, G. gracilis and G. corneum exhibited lower gel strength, consistent with their agar composition. WB-treated samples demonstrated superior antioxidant retention, while US treatment was more effective in preserving color stability. The findings highlight macroalgae as a viable and sustainable alternative to conventional hydrocolloids, reinforcing their potential as natural gelling agents, thickeners, and stabilizers for the food and pharmaceutical industries. This study provides a comparative evaluation of WB, US, and USWB extraction methods, offering insights into optimizing hydrocolloid extraction for enhanced functionality and sustainability.

Optimization and evaluation of a simplified green biorefinery for alginate extraction from sugar kelp (Saccharina latissima)

A simplified two-stage ultrasound-assisted biorefinery process for sodium alginate extraction from sugar kelp (Saccharina latissima) was developed using green solvents. The process yielded three distinct fractions: fucoidan/laminarin (S1), sodium alginate (S2), and cellulose (P2). The results were analyzed with response surface methodology. Key parameters, including sonication amplitude, time, and pH, were evaluated, and sonication energy was introduced as a predictive factor to improve model accuracy. Mathematical optimization of the response surface model identified an optimal sodium alginate yield of 76.4 % at pH 2 and 432.2 kJ of sonication energy. Fourier-transform infrared spectroscopy (FTIR) confirmed effective sodium alginate fractionation, and molecular weight analysis correlated viscosity with alginate quality. Inductively coupled plasma mass spectrometry (ICP-MS) showed reduced heavy metal content in both fucoidan/laminarin and alginate, indicating an improved safety profile for potential food and nutritional applications. This scalable and eco-friendly biorefinery highlights an environmentally sustainable approach for sodium alginate production, maximizing biomass valorization and ensuring product safety.

Recent developments in alginate-based nanocomposite coatings and films for biodegradable food packaging applications

Packaging made of plastic harms the environment. Thus, polysaccharide edible films are becoming a popular food packaging solution. Alginate is a biopolymer derived from seaweed that has the potential to create food packaging materials that are environmentally friendly and biodegradable. This article explores the potential use of nanocomposite coatings and films made from alginate as an alternative to petroleum-based polymers in the food industry. Alginate is desirable for food packaging due to its low cost, high nutritional value, renewability, low oxygen permeability, biodegradability, and biocompatibility. This article delves into alginate's history and extraction processes and covers techniques for modifying its physical and chemical properties using blended polymers and additives. Alginate-based coatings and films have been found to improve the mechanical properties and sensory characteristics of various food items and prolong the shelf life of perishable items by regulating oxygen and moisture levels and as a barrier against microbial growth. Further investigation is necessary to maximize the performance of alginate-based polymers in various food industry applications. Future prospects call on advancements in their physicochemical and functional characteristics to increase the acceptability of alginate-based nanocomposite coatings and films for biodegradable food packaging applications.

Value-added utilization technologies for seaweed processing waste in a circular economy: Developing a sustainable modern seaweed industry

The global seaweed industry annually consumes approximately 600,000 tons of dried algal biomass to produce algal hydrocolloids, yet only 15-30% of this biomass is utilized, with the remaining 70-85% discarded or released as scum or wastewater during the hydrocolloid extraction process. This residual biomass is often treated as waste and not considered for further commercial use, which contradicts the principles of sustainable development. In reality, the residual algal biomass could be employed to extract additional biochemical components, such as pigments, proteins, and cellulose, and these ingredients have important application prospects in the food sector. According to the biorefinery concept, recycling various products alongside the principal product enhances overall biomass utilization. Transitioning from traditional single-product processes to multi-product biorefineries, however, raises operating costs, presenting a significant challenge. Alternatively, developing value-added utilization technologies that target seaweed waste without altering existing processes is gaining traction among industry practitioners. Current advancements include methods such as separation and extraction of residual biomass, anaerobic digestion, thermochemical conversion, enzymatic treatment, functionalized modification of algal scum, and efficient utilization through metabolic engineering. These technologies hold promise for converting seaweed waste into alternative proteins, dietary supplements, and bioplastics for food packaging. Combining multiple technologies may offer the most effective strategy for future seaweed waste treatment. Nonetheless, most research on value-added waste utilization remains at the laboratory scale, necessitating further investigation at pilot and commercial scales.

Application of Ulva lactuca polysaccharide in the preservation of refrigerated of Lateolabrax maculatus fillets

This study aimed to explore the use of Ulva lactuca polysaccharide (ULP) as a preservative for perch (Lateolabrax maculatus) fillets stored under refrigeration at 4 °C. Fresh perch fillets were treated with ULP (7-10 kDa) and potassium sorbate, respectively, to evaluate their effectiveness in inhibiting bacterial growth and maintain freshness. A 0.5% ULP solution significantly decreased the pH value, total volatile basic nitrogen value, thiobarbituric acid value, and total bacterial count of perch fillets. ULP solution delayed the changes in whiteness and texture of fillets, as well as protein degradation. The acute toxicity experiment further evaluates the safety and reliability of ULP. Simultaneously, utilizing 16S rRNA techniques, the ULP solution inhibited microorganisms known for their strong spoilage capabilities, such as Pseudomonas, Actinetobacter, and Shewanella. Microorganisms with a weaker ability to cause corruption became the dominant bacteria, such as Acetobacter, Lactobacillus, and Faecalibacterium, thereby exerting a degree of inhibition against spoilage.

Polysaccharides from the Sargassum and Brown Algae Genus: Extraction, Purification, and Their Potential Therapeutic Applications

Brown macroalgae represent one of the most proliferative groups of living organisms in aquatic environments. Due to their abundance, they often cause problems in aquatic and terrestrial ecosystems, resulting in health problems in humans and the death of various aquatic species. To resolve this, the application of Sargassum has been sought in different research areas, such as food, pharmaceuticals, and cosmetics, since Sargassum is an easy target for study and simple to obtain. In addition, its high content of biocompounds, such as polysaccharides, phenols, and amino acids, among others, has attracted attention. One of the valuable components of brown macroalgae is their polysaccharides, which present interesting bioactivities, such as antiviral, antimicrobial, and antitumoral, among others. There is a wide variety of methods of extraction currently used to obtain these polysaccharides, such as supercritical fluid extraction (SFE), pressurized liquid extraction (PLE), subcritical water extraction (SCWE), ultrasound-assisted extraction (UAE), enzyme-assisted extraction (EAE), and microwave-assisted extraction (MAE). Therefore, this work covers the most current information on the methods of extraction, as well as the purification used to obtain a polysaccharide from Sargassum that is able to be utilized as alginates, fucoidans, and laminarins. In addition, a compilation of bioactivities involving brown algae polysaccharides in in vivo and in vitro studies is also presented, along with challenges in the research and marketing of Sargassum-based products that are commercially available.

Purification and Molecular Characterization of Fucoidan Isolated from Ascophyllum nodosum Brown Seaweed Grown in Ireland

The present study investigates the molecular characteristics of fucoidan obtained from the brown Irish seaweed Ascophyllum nodosum, employing hydrothermal-assisted extraction (HAE) followed by a three-step purification protocol. The dried seaweed biomass contained 100.9 mg/g of fucoidan, whereas optimised HAE conditions (solvent, 0.1N HCl; time, 62 min; temperature, 120 °C; and solid to liquid ratio, 1:30 (w/v)) yielded 417.6 mg/g of fucoidan in the crude extract. A three-step purification of the crude extract, involving solvents (ethanol, water, and calcium chloride), molecular weight cut-off filter (MWCO; 10 kDa), and solid-phase extraction (SPE), resulted in 517.1 mg/g, 562.3 mg/g, and 633.2 mg/g of fucoidan (p < 0.05), respectively. In vitro antioxidant activity, as determined by 1,1-diphenyl-2-picryl-hydrazyl radical scavenging and ferric reducing antioxidant power assays, revealed that the crude extract exhibited the highest antioxidant activity compared to the purified fractions, commercial fucoidan, and ascorbic acid standard (p < 0.05). The molecular attributes of biologically active fucoidan-rich MWCO fraction was characterised by quadruple time of flight mass spectrometry and Fourier-transform infrared (FTIR) spectroscopy. The electrospray ionisation mass spectra of purified fucoidan revealed quadruply ([M+4H]4+) and triply ([M+3H]3+) charged fucoidan moieties at m/z 1376 and m/z 1824, respectively, and confirmed the molecular mass 5444 Da (~5.4 kDa) from multiply charged species. The FTIR analysis of both purified fucoidan and commercial fucoidan standard exhibited O-H, C-H, and S=O stretching which are represented by bands at 3400 cm-1, 2920 cm-1, and 1220-1230 cm-1, respectively. In conclusion, the fucoidan recovered from HAE followed by a three-step purification process was highly purified; however, purification reduced the antioxidant activity compared to the crude extract.

Marine glycoproteins: a mine of their structures, functions and potential applications

Many bioactive compounds are reported from marine organisms, which are significantly different from those found in terrestrial organisms regarding their chemical structures and pharmacological activities. Marine glycoproteins (MGs) have aroused increasing attention as a good nutrient source owing to their potential applications in medicine, cosmetics and food. However, there is a lack of a comprehensive study on MGs to help readers understand the current state of research on marine-derived glycoproteins. The current review compiles the recent progress made on the structures and functions of MGs with future perspectives to maximize their value and applications via bibliometric analysis methods for the first time. The current research on MGs appears mostly limited to the laboratory, with no large-scale production of marine glycoproteins developed. The sugar chains are bound to proteins through covalent bonds that can readily be cleaved leading to difficultly in their separation and purification. Health effects attributed to MGs include treatment of inflammatory diseases, as well as anti-oxidant, immune modulation, anti-tumor, hypolipidemic, hypoglycemic, anti-bacterial and anti-freeze activities. This review can not only deepen the understanding of the functions of MGs, but also lay an important foundation for the further development and utilization of marine resources.

Prospects of dietary seaweeds and their bioactive compounds in sustainable poultry production systems: A symphony of good things?

Modern poultry production systems face numerous economic, environmental, and social sustainability challenges that threaten their viability and acceptability as a major source of animal protein. As scientists and producers scramble to find cost-effective and socially acceptable solutions to these challenges, the dietary use of marine macroalgae (seaweeds) could be an ingenious option. Indeed, the incredible array of nutritive and bioactive compounds present in these macroscopic marine organisms can be exploited as part of sustainable poultry production systems of the future. Incorporating seaweeds in poultry diets could enhance feed utilization efficiency, growth performance, bird health, meat stability and quality, and consumer and environmental health. Theoretically, these benefits are mediated through the putative antiviral, antibacterial, antifungal, antioxidant, anticarcinogenic, anti-inflammatory, anti-allergic, antithrombotic, neuroprotective, hypocholesterolemic, and hypoglycemic properties of seaweed bioactive compounds. Despite this huge potential, exploitation of seaweed for poultry production appears to be constrained by a variety of factors such as high fibre, phenolics, and ash content. In addition, conflicting findings are often reported when seaweeds or their extracts are used in poultry feeding trials. Therefore, the purpose of this review paper is to collate information on the production, phytochemical components, and nutritive value of different seaweed species. It provides an overview ofin vivoeffects of dietary seaweeds as measured by nutrient utilization efficiency, growth performance, and product quality and stability in poultry. The utility of dietary seaweeds in sustainable poultry production systems is explored, while gaps that require further research are highlighted. Finally, opportunities that exist for enhancing the utility of seaweeds as a vehicle for sustainable production of functional poultry products for better global food and nutrition security are presented.

Novel Technologies for Seaweed Polysaccharides Extraction and Their Use in Food with Therapeutically Applications—A Review

The use of seaweed for therapeutic purposes is ancient, but only in the last decade, with advanced technologies, has it been possible to extract seaweed’s bioactive compounds and test their potential properties. Algal metabolites possess nutritional properties, but they also exhibit antioxidant, antimicrobial, and antiviral activities, which allow them to be involved in several pharmaceutical applications. Seaweeds have been incorporated since ancient times into diets as a whole food. With the isolation of particular seaweed compounds, it would be possible to develop new types of food with therapeutically properties. Polysaccharides make up the majority of seaweed biomass, which has triggered an increase in interest in using seaweed for commercial purposes, particularly in the production of agar, carrageenan, and alginate. The bio-properties of polysaccharides are strictly dependent to their chemical characteristics and structure, which varies depending on the species, their life cycles, and other biotic and abiotic factors. Through this review, techniques for seaweed polysaccharides extraction are reported, with studies addressing the advantages for human health from the incorporation of algal compounds as dietary supplements and food additives.

Marine Bioactive Compounds Derived from Macroalgae as New Potential Players in Drug Delivery Systems: A Review

The marine algal ecosystem is characterized by a rich ecological biodiversity and can be considered as an unexploited resource for the discovery and isolation of novel bioactive compounds. In recent years, marine macroalgae have begun to be explored for their valuable composition in bioactive compounds and opportunity to obtain different nutraceuticals. In comparison with their terrestrial counterparts, Black Sea macroalgae are potentially good sources of bioactive compounds with specific and unique biological activities, insufficiently used. Macroalgae present in different marine environments contain several biologically active metabolites, including polysaccharides, oligosaccharides, polyunsaturated fatty acids, sterols, proteins polyphenols, carotenoids, vitamins, and minerals. As a result, they have received huge interest given their promising potentialities in supporting antitumoral, antimicrobial, anti-inflammatory, immunomodulatory, antiangiogenic, antidiabetic, and neuroprotective properties. An additional advantage of ulvans, fucoidans and carrageenans is the biocompatibility and limited or no toxicity. This therapeutic potential is a great natural treasure to be exploited for the development of novel drug delivery systems in both preventive and therapeutic approaches. This overview aims to provide an insight into current knowledge focused on specific bioactive compounds, which represent each class of macroalgae e.g., ulvans, fucoidans and carrageenans, respectively, as valuable potential players in the development of innovative drug delivery systems.

Advancement of biorefinery-derived platform chemicals from macroalgae: a perspective for bioethanol and lactic acid

The extensive growth of energy and plastic demand has raised concerns over the depletion of fossil fuels. Moreover, the environmental conundrums worldwide integrated with global warming and improper plastic waste management have led to the development of sustainable and environmentally friendly biofuel (bioethanol) and biopolymer (lactic acid, LA) derived from biomass for fossil fuels replacement and biodegradable plastic production, respectively. However, the high production cost of bioethanol and LA had limited its industrial-scale production. This paper has comprehensively reviewed the potential and development of third-generation feedstock for bioethanol and LA production, including significant technological barriers to be overcome for potential commercialization purposes. Then, an insight into the state-of-the-art hydrolysis and fermentation technologies using macroalgae as feedstock is also deliberated in detail. Lastly, the sustainability aspect and perspective of macroalgae biomass are evaluated economically and environmentally using a developed cascading system associated with techno-economic analysis and life cycle assessment, which represent the highlights of this review paper. Furthermore, this review provides a conceivable picture of macroalgae-based bioethanol and lactic acid biorefinery and future research directions that can be served as an important guideline for scientists, policymakers, and industrial players.

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Current application of algae derivatives for bioplastic production: A review

Improper use of conventional plastics poses challenges for sustainable energy and environmental protection. Algal derivatives have been considered as a potential renewable biomass source for bioplastic production. Algae derivatives include a multitude of valuable substances, especially starch from microalgae, short-chain length polyhydroxyalkanoates (PHAs) from cyanobacteria, polysaccharides from marine and freshwater macroalgae. The algae derivatives have the potential to be used as key ingredients for bioplastic production, such as starch and PHAs or only as an additive such as sulfated polysaccharides. The presence of distinctive functional groups in algae, such as carboxyl, hydroxyl, and sulfate, can be manipulated or tailored to provide desirable bioplastic quality, especially for food, pharmaceutical, and medical packaging. Standardizing strains, growing conditions, harvesting and extracting algae in an environmentally friendly manner would be a promising strategy for pollution control and bioplastic production.

Hydrothermal systems to obtain high value-added compounds from macroalgae for bioeconomy and biorefineries

The search of sustainable and environmentally friendly alternatives to obtain compounds for different industrial sectors has grown exponentially. Following the principles of biorefinery and circular bioeconomy, processes in which the use of natural resources such as macroalgae biomass is prioritized are required. This review focuses on a description of the relevance, application and engineering platforms of hydrothermal systems and the operational conditions depending on the target as an innovative technology and bio-based solution for macroalgae fractionation in order to recover profitable products for industries and investors. In this sense, hydrothermal treatments represent a promising alternative for obtaining different high value-added compounds from this biomass; since, the different variations in terms of operating conditions, gives great versatility to this technology compared to other types of processing, allowing it to be adapted depending on the objective, whether it is working under sub/super critical conditions, thus expanding its field of application.

Development of technology of creams using hydrocolloids

The article presents a scientific study of the functional and technological properties of hydrocolloids, namely thickeners of polysaccharide nature, which are used as thickeners and stabilizers in dessert products. According to the monitoring of literature sources and the experience of manufacturers, the most commonly used thickeners of polysaccharide nature are carrageenan, locust bean gum, xanthan gum, pectin, starch, etc. However, each of these polysaccharides has both positive and negative sides, more polysaccharides are able to form dense gels, but with a high synergistic effect. Thickeners, such as k-carrageenan, low-esterified pectins, can form gels only in the presence of Са2+. There are also polysaccharides that form gels only at low temperatures and are not stable during external factors (temperature of sale and storage, mechanical impact, etc.). Therefore, the study was conducted on the combination of polysaccharides in order to obtain creams with an airy gel-like structure. It has been determined, that it is expedient to use the combination "xanthan gum 0.75 % – locust bean gum 0.5 %" to obtain cream

Comparative Analysis of the Chemical Composition and Physicochemical Properties of the Mucilage Extracted from Fresh and Dehydrated Opuntia ficus indica Cladodes

The development of sustainable extraction methods to obtain natural products constitutes a challenge for the food industry. The aim of this work was to compare yield, separation efficiency, chemical composition, and physicochemical properties of the mucilage extracted from fresh cladodes (FNM) and mucilage extracted from dehydrated cladodes (DNM) of O. ficus indica. Suspensions of fresh and dehydrated cladodes (4% w/w) were prepared for mucilage extraction by using a mechanical separation process. Subsequently, the separated mucilage was precipitated with ethyl alcohol (1:2 v/v) then, yield and separation efficiency were determined. The mucilage was characterized by measuring Z potential, viscosity, color, and texture attributes. Additionally, chemical proximate analysis, scanning electron microscopy, and thermogravimetric analysis (TGA) were conducted. No significant differences (p < 0.05) were detected in the yield and separation efficiencies between samples. Nevertheless, the dehydration process of cladodes prior to mucilage extraction increased protein, ashes, nitrogen free extract, and calcium content. The viscosity was higher in DNM than in FNM. The TGA revealed a different thermal behavior between samples. In addition, the DNM showed lower L (darkness/lightness), cohesiveness, adhesiveness, and springiness values than those of FNM. These results support that differences found between the chemical and physicochemical properties of DNM and those of FNM will determine the applications of the mucilage obtained from the O. ficus indica cladodes in the food, pharmaceutical, and cosmetic industries.

Influence of molecular weight fractionation on the antimicrobial and anticancer properties of a fucoidan rich-extract from the macroalgae Fucus vesiculosus

The objective of this study was to investigate the antimicrobial and anticancer properties of a fucoidan extract and subsequent fractions isolated from the macroalgae Fucus vesiculosus. The fractions obtained (>300 kDa, <300 kDa, <100 kDa, <50 kDa and <10 kDa) could inhibit the growth of B. subtilis, E. coli, L. innocua and P. fluorescens when assayed at concentrations between 12,500 and 25,000 ppm. The bacterial growth was monitored by optical density (OD) measurements (600 nm, 24 h) at 30 °C or 37 °C, depending upon on the strain used. The extracted fractions were also tested for cytotoxicity against brain glioblastoma cancer cells using the Alamar Blue assay for 24 h, 48 h and 6 days. The >300 kDa fraction presented the lowest IC50 values (0.052% - 24 h; 0.032% - 6 days). The potential bioactivity of fucoidan as an antimicrobial and anticancer agent was demonstrated in this study. Hence, the related mechanisms of action should be explored in a near future.

Seaweed polysaccharides: Emerging extraction technologies, chemical modifications and bioactive properties

Nowadays, consumers are increasingly aware of the relationship between diet and health, showing a greater preference of products from natural origin. In the last decade, seaweeds have outlined as one of the natural sources with more potential to obtain bioactive carbohydrates. Numerous seaweed polysaccharides have aroused the interest of the scientific community, due to their biological activities and their high potential on biomedical, functional food and technological applications. To obtain polysaccharides from seaweeds, it is necessary to find methodologies that improve both yield and quality and that they are profitable. Nowadays, environmentally friendly extraction technologies are a viable alternative to conventional methods for obtaining these products, providing several advantages like reduced number of solvents, energy and time. On the other hand, chemical modification of their structure is a useful approach to improve their solubility and biological properties, and thus enhance the extent of their potential applications since some uses of polysaccharides are still limited. The present review aimed to compile current information about the most relevant seaweed polysaccharides, available extraction and modification methods, as well as a summary of their biological activities, to evaluate knowledge gaps and future trends for the industrial applications of these compounds.Key teaching pointsStructure and biological functions of main seaweed polysaccharides.Emerging extraction methods for sulfate polysaccharides.Chemical modification of seaweeds polysaccharides.Potential industrial applications of seaweed polysaccharides.Biological activities, knowledge gaps and future trends of seaweed polysaccharides.

Antimicrobials from Seaweeds for Food Applications

The exponential growth of emerging multidrug-resistant microorganisms, including foodborne pathogens affecting the shelf-life and quality of foods, has recently increased the needs of the food industry to search for novel, natural and eco-friendly antimicrobial agents. Macroalgae are a bio-diverse group distributed worldwide, known to produce multiple compounds of diverse chemical nature, different to those produced by terrestrial plants. These novel compounds have shown promising health benefits when incorporated into foods, including antimicrobial properties. This review aims to provide an overview of the general methods and novel compounds with antimicrobial properties recently isolated and characterized from macroalgae, emphasizing the molecular pathways of their antimicrobial mechanisms of action. The current scientific evidence on the use of macroalgae or macroalgal extracts to increase the shelf-life of foods and prevent the development of foodborne pathogens in real food products and their influence on the sensory attributes of multiple foods (i.e., meat, dairy, beverages, fish and bakery products) will also be discussed, together with the main challenges and future trends of the use of marine natural products as antimicrobials.

The Use of Invasive Algae Species as a Source of Secondary Metabolites and Biological Activities: Spain as Case-Study

In the recent decades, algae have proven to be a source of different bioactive compounds with biological activities, which has increased the potential application of these organisms in food, cosmetic, pharmaceutical, animal feed, and other industrial sectors. On the other hand, there is a growing interest in developing effective strategies for control and/or eradication of invasive algae since they have a negative impact on marine ecosystems and in the economy of the affected zones. However, the application of control measures is usually time and resource-consuming and not profitable. Considering this context, the valorization of invasive algae species as a source of bioactive compounds for industrial applications could be a suitable strategy to reduce their population, obtaining both environmental and economic benefits. To carry out this practice, it is necessary to evaluate the chemical and the nutritional composition of the algae as well as the most efficient methods of extracting the compounds of interest. In the case of northwest Spain, five algae species are considered invasive: Asparagopsis armata, Codium fragile, Gracilaria vermiculophylla, Sargassum muticum, and Grateulopia turuturu. This review presents a brief description of their main bioactive compounds, biological activities, and extraction systems employed for their recovery. In addition, evidence of their beneficial properties and the possibility of use them as supplement in diets of aquaculture animals was collected to illustrate one of their possible applications.

Diversity of Sulfated Polysaccharides From Cell Walls of Coenocytic Green Algae and Their Structural Relationships in View of Green Algal Evolution

Seaweeds biosynthesize sulfated polysaccharides as key components of their cell walls. These polysaccharides are potentially interesting as biologically active compounds. Green macroalgae of the class Ulvophyceae comprise sulfated polysaccharides with great structural differences regarding the monosaccharide constituents, linearity of their backbones, and presence of other acidic substituents in their structure, including uronic acid residues and pyruvic acid. These structures have been thoroughly studied in the Ulvales and Ulotrichales, but only more recently have they been investigated with some detail in ulvophytes with giant multinucleate (coenocytic) cells, including the siphonous Bryopsidales and Dasycladales, and the siphonocladous Cladophorales. An early classification of these structurally heterogeneous polysaccharides was based on the presence of uronic acid residues in these molecules. In agreement with this classification based on chemical structures, sulfated polysaccharides of the orders Bryopsidales and Cladophorales fall in the same group, in which this acidic component is absent, or only present in very low quantities. The cell walls of Dasycladales have been less studied, and it remains unclear if they comprise sulfated polysaccharides of both types. Although in the Bryopsidales and Cladophorales the most important sulfated polysaccharides are arabinans and galactans (or arabinogalactans), their major structures are very different. The Bryopsidales produce sulfated pyruvylated 3-linked β-d-galactans, in most cases, with ramifications on C6. For some species, linear sulfated pyranosic β-l-arabinans have been described. In the Cladophorales, also sulfated pyranosic β-l-arabinans have been found, but 4-linked and highly substituted with side chains. These differences are consistent with recent molecular phylogenetic analyses, which indicate that the Bryopsidales and Cladophorales are distantly related. In addition, some of the Bryopsidales also biosynthesize other sulfated polysaccharides, i.e., sulfated mannans and sulfated rhamnans. The presence of sulfate groups as a distinctive characteristic of these biopolymers has been related to their adaptation to the marine environment. However, it has been shown that some freshwater algae from the Cladophorales also produce sulfated polysaccharides. In this review, structures of sulfated polysaccharides from bryopsidalean, dasycladalean, and cladophoralean green algae studied until now are described and analyzed based on current phylogenetic understanding, with the aim of unveiling the important knowledge gaps that still exist.