Reserve, structural and extracellular polysaccharides of Chlorella vulgaris: A holistic approach

Influence of Biogenic Material Content on the Biodegradability of Styrene-Butadiene Composites with Incorporated Chlorella vulgaris Biomass

Bio-fillers are intensively studied for advanced polymer composite circular design and production. In this context, the algal biomass may be considered an important and relatively low-cost resource, when harvested as a by-product from wastewater treatment plants. The biomass of the algal species Chlorella vulgaris is frequently used in this type of environmental process, and its macro constituents' composition ranges from around 15-25% carbohydrates, 10-20% lipids, and 50-60% proteins. Poly (styrene-butadiene-styrene) (SBS) copolymers have a matrix composed of glassy polystyrene domains connected by flexible polybutadiene segments. Although the physical-mechanical properties of SBS copolymers recommend them for many industrial applications, they have the drawback of low biodegradability. This study aimed to assess the aerobic biodegradability of polymer composites by integrating biomass from Chlorella vulgaris at varying mass percentages of 5, 10, and 20% into SBS copolymer composites. Biodegradation tests were conducted under industrial composting conditions (58 °C and 50% relative humidity) for 180 days. The biodegradability of materials was evaluated by measuring the CO2 produced in each vessel during the study period. Potential correlations between the amount of carbon dioxide released and the percentage of biomass added to the polymer matrix were examined. Structural and morphological changes were assessed using Fourier Transform infrared spectroscopy (FTIR), thermal analysis (DSC), and scanning electron microscopy (SEM). Physical and chemical testing revealed a decrease in sample density after the industrial composting test, along with noticeable changes in melt flow index (MFI). The observed physical and chemical changes, coupled with FTIR, SEM, and DSC data, indicate increased cross-linking and higher porosity in biodegraded polymer structures with higher biomass content. This behavior is likely due to the formation of cross-linked connections between polymer chains and polypeptide chains resulting from protein degradation, enhancing connections between polystyrene units facilitated by peptide bonds with the benzene units of the styrene blocks within the polymer matrix.

A sulfated exopolysaccharide derived from Chlorella sp. exhibiting in vitro anti-α-D-Glucosidase activity

There is a great scientific curiosity to discover all environments sheltering microalgae, especially those with exceptional characteristics from coldest to hottest ones, the purpose remains to explore the potential of the native microalgae flora and the research for new bioactive compounds. This study aimed to isolate a polysaccharide-producing microalga from an extreme ecosystem and to evaluate its capacity to inhibit the α-D-glucosidase enzyme. Chlorella strain is isolated from hypersaline Lake in the Algerian desert. The exopolysaccharide extraction was performed by the concentration of free-cell supernatant in a rotary evaporator. The infrared analysis showed a characteristic footprint of carbohydrates with particular functional groups, such as sulfate. Gas chromatography-mass spectrometry has revealed a hetero-exopolysaccharide composed of galactose 35.75%, glucose 21.13%, xylose 16.81%, fructose 6.96%, arabinose 5.10%, and glucuronic acid 2.68%. The evaluation of the anti-hyperglycemic activity demonstrated a significant α-D-glucosidase inhibition of 80.94 ± 0.01% at 10 mg mL-1 with IC50 equal to 4.31 ± 0.20 mg mL-1. This study opens a vast prospect to use exopolysaccharides as natural nutraceutical or food additive.

Microalgae's polysaccharides, are they potent antioxidants? Critical review

The scientific community continue to explore novel bioactive molecules by investigating natural origins; microalgae are photosynthetic organisms considered as a sustainable resource to use in many fields. They present a high diversity in species and richness in terms of attractive bio-compounds. The aim of this review is to (1) provide first an overview of current issues related to oxidative stress, and propose a natural metabolite derived from eukaryotic and prokaryotic microalgae; 'polysaccharides' as a powerful antioxidant agent, then, (2) organize the available data on the antioxidant potential of polysaccharides derived from the main microalgal groups (red microalgae, green microalgae, and cyanobacteria) and especially highlighted the key species of each group (Porphyridium sp., Chlorella sp., and Arthrospira sp., respectively), meanwhile, (3) we described the chemical composition of polysaccharides from each class, and (4) we cite briefly the most factors affecting the antioxidant activity of these molecules. Finally, we explored the major challenges and gaps found to require more investigation.

Water-Soluble Saccharina latissima Polysaccharides and Relation of Their Structural Characteristics with In Vitro Immunostimulatory and Hypocholesterolemic Activities

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.

Stabilization of Natural Pigments in Ethanolic Solutions for Food Applications: The Case Study of Chlorella vulgaris

Chlorella vulgaris is a green microalga with a high chlorophyll content, representing a valuable source of green pigments for food applications. As the application of whole biomass can promote an unpleasant fish-like flavor, the use of chlorophyll extract can overcome this drawback. However, chlorophylls tend to easily degrade when out of the chloroplasts, decreasing their potential as a food ingredient. Thus, to study the suitable conditions for isolated chlorophylls preservation, in this work, the influence of temperature (4 to 60 °C), light (dark or 24 h photoperiod), alkaline conditions (with or without aqueous NaOH addition), and modified atmosphere (air or argon atmosphere) on the stability of the color in ethanolic solutions obtained from C. vulgaris were studied. The loss of green color with temperature followed the first-order kinetics, with an activation energy of 74 kJ/mol. Below 28 °C and dark conditions were suitable to preserve isolated chlorophylls. The addition of NaOH and an inert argon-rich atmosphere did not exhibit a statistically positive effect on color preservation. In the case study, cooked cold rice was colored to be used in sushi. The color remained stable for up to 3 days at 4 °C. Therefore, this work showed that C. vulgaris chlorophylls could be preserved in ethanolic solutions at room or lower temperatures when protected from light, allowing them to obtain a suitable natural food ingredient to color foodstuffs.

A commercial blend of macroalgae and microalgae promotes digestibility, growth performance, and muscle nutritional value of European seabass (Dicentrarchus labrax L.) juveniles

Algae can leverage aquaculture sustainability and improve the nutritional and functional value of fish for human consumption, but may pose challenges to carnivorous fish. This study aimed to evaluate the potential of a commercial blend of macroalgae (Ulva sp. and Gracilaria gracilis) and microalgae (Chlorella vulgaris and Nannochloropsis oceanica) in a plant-based diet up to 6% (dry matter basis) on digestibility, gut integrity, nutrient utilization, growth performance, and muscle nutritional value of European seabass juveniles. Fish (11.3 ± 2.70 g) were fed with isoproteic, isolipidic, and isoenergetic diets: (i) a commercial-type plant-based diet with moderate fishmeal (125 g kg^-1 DM basis) and without algae blend (control diet; Algae0), (ii) the control diet with 2% algae blend (Algae2), (iii) the control diet with 4% algae blend (Algae4), and (iv) the control diet with 6% algae blend (Algae6) for 12 weeks. The digestibility of experimental diets was assessed in a parallel study after 20 days. Results showed that most nutrients and energy apparent digestibility coefficients were promoted by algae blend supplementation, with a concomitant increase in lipid and energy retention efficiencies. Growth performance was significantly promoted by the algae blend, the final body weight of fish fed Algae6 being 70% higher than that of fish fed Algae0 after 12 weeks, reflecting up to 20% higher feed intake of algae-fed fish and the enhanced anterior intestinal absorption area (up to 45%). Whole-body and muscle lipid contents were increased with dietary algae supplementation levels by up to 1.79 and 1.74 folds in Algae 6 compared to Algae0, respectively. Even though the proportion of polyunsaturated fatty acids was reduced, the content of EPA and DHA in the muscle of algae-fed fish increased by nearly 43% compared to Algae0. The skin and filet color of juvenile European seabass were significantly affected by the dietary inclusion of the algae blend, but changes were small in the case of muscle, meeting the preference of consumers. Overall results highlight the beneficial effects of the commercial algae blend (Algaessence^®) supplementation in plant-based diets for European seabass juveniles, but feeding trials up to commercial-size fish are needed to fully assess its potential.

Bacterial polysaccharides-A big source for prebiotics and therapeutics

Bacterial polysaccharides are unique due to their higher purity, hydrophilic nature, and a finer three-dimensional fibrous structure. Primarily, these polymers provide protection, support, and energy to the microorganism, however, more recently several auxiliary properties of these biopolymers have been unmasked. Microbial polysaccharides have shown therapeutic abilities against various illnesses, augmented the healing abilities of the herbal and Western medicines, improved overall health of the host, and have exerted positive impact on the growth of gut dwelling beneficial bacteria. Specifically, the review is discussing the mechanism through which bacterial polysaccharides exert anti-inflammatory, antioxidant, anti-cancer, and anti-microbial properties. In addition, they are holding promising application in the 3D printing. The review is also discussing a perspective about the metagenome-based screening of polysaccharides, their integration with other cutting-edge tools, and synthetic microbiome base intervention of polysaccharides as a strategy for prebiotic intervention. This review has collected interesting information about the bacterial polysaccharides from Google Scholar, PubMed, Scopus, and Web of Science databases. Up to our knowledge, this is the first of its kind review article that is summarizing therapeutic, prebiotics, and commercial application of bacterial polysaccharides.

Prospects of microbial polysaccharides-based hybrid constructs for biomimicking applications

Polysaccharides are biobased polymers obtained from renewable sources. They exhibit various interesting features including biocompatibility, biodegradability, and nontoxicity. Microbial polysaccharides are produced by several microorganisms including yeast, fungi, algae, and bacteria. Microbial polysaccharides have gained high importance in biotechnology due to their novel physiochemical characteristics and composition. Among microbial polysaccharides, xanthan, alginate, gellan, and dextran are the most commonly reported polysaccharides for the development of biomimetic materials for biomedical applications including targeted drug delivery, wound healing, and tissue engineering. Several chemical and physical cross-linking reactions are performed to increase their technological and functional properties. Owning to the broad-scale applications of microbial polysaccharides, this review aims to summarize the characteristics with different ways of physical/chemical crosslinking for polysaccharide regulation. Recently, several biopolymers have gained high importance due to their biologically active properties. This will help in the formation of bioactive nutraceuticals and functional foods. This review provides a perspective on microbial polysaccharides, with special emphasis given to applications in promising biosectors and the subsequent advancement on the discovery and development of new polysaccharides for adding new products.

Fractionation of the water insoluble part of the heterotrophic mutant green microalga Parachlorella kessleri HY1 (Chlorellaceae) biomass: Identification and structure of polysaccharides

The water-insoluble part of Parachlorella kessleri HY1 biomass was subjected to the extraction of cell-wall polysaccharides using polar aprotic solvents (DMSO, LiCl/DMSO) and aqueous alkaline solutions (0.1, 1 and 4 mol·l^-1 of NaOH). Proteins predominated in all the crude extracts and in the insoluble residues were partially removed by treatment with proteolytic enzymes (pepsin and pronase), and in some cases with the HCl/H₂O₂ reagent, yielding purified polysaccharide-enriched fractions. These treatments led to the solubilisation of some products in water. The composition and structure of isolated polysaccharides were characterised based on monosaccharide composition, glycosidic linkage and spectroscopic analyses. The DMSO extract contained mainly proteins, and polysaccharides were not detected. The water-soluble parts isolated from the LiCl/DMSO extract contained α-l-rhamnan, α-d-glucan and β-d-glucogalactan; the water-insoluble part contained (1 → 4)-β-d-xylan, first isolated from the biomass of green microalgae. The alkali extracts contained polysaccharides of similar structure, and also water-insoluble (1 → 4)-β-d-mannan. The insoluble part after all extractions contained α-chitin as the main polysaccharide, which was confirmed by spectroscopic methods. All these polysaccharides can play a certain role in the cell wall structure of this microalga.

Insights into cell wall disintegration of Chlorella vulgaris

With their ability of CO2 fixation using sunlight as an energy source, algae and especially microalgae are moving into the focus for the production of proteins and other valuable compounds. However, the valorization of algal biomass depends on the effective disruption of the recalcitrant microalgal cell wall. Especially cell walls of Chlorella species proved to be very robust. The wall structures that are responsible for this robustness have been studied less so far. Here, we evaluate different common methods to break up the algal cell wall effectively and measure the success by protein and carbohydrate release. Subsequently, we investigate algal cell wall features playing a role in the wall's recalcitrance towards disruption. Using different mechanical and chemical technologies, alkali catalyzed hydrolysis of the Chlorella vulgaris cells proved to be especially effective in solubilizing up to 56 wt% protein and 14 wt% carbohydrates of the total biomass. The stepwise degradation of C. vulgaris cell walls using a series of chemicals with increasingly strong conditions revealed that each fraction released different ratios of proteins and carbohydrates. A detailed analysis of the monosaccharide composition of the cell wall extracted in each step identified possible factors for the robustness of the cell wall. In particular, the presence of chitin or chitin-like polymers was indicated by glucosamine found in strong alkali extracts. The presence of highly ordered starch or cellulose was indicated by glucose detected in strong acidic extracts. Our results might help to tailor more specific efforts to disrupt Chlorella cell walls and help to valorize microalgae biomass.

Starch Rich Chlorella vulgaris: High-Throughput Screening and Up-Scale for Tailored Biomass Production

The use of microalgal starch has been studied in biorefinery frameworks to produce bioethanol or bioplastics, however, these products are currently not economically viable. Using starch-rich biomass as an ingredient in food applications is a novel way to create more value while expanding the product portfolio of the microalgal industry. Optimization of starch production in the food-approved species Chlorella vulgaris was the main objective of this study. High-throughput screening of biomass composition in response to multiple stressors was performed with FTIR spectroscopy. Nitrogen starvation was identified as an important factor for starch accumulation. Moreover, further studies were performed to assess the role of light distribution, investigating the role of photon supply rates in flat panel photobioreactors. Starch-rich biomass with up to 30% starch was achieved in cultures with low inoculation density (0.1 g L−1) and high irradiation (1800 µmol m−2 s−1). A final large-scale experiment was performed in 25 L tubular reactors, achieving a maximum of 44% starch in the biomass after 12 h in nitrogen starved conditions.

Static Magnetic Fields Effects on Polysaccharides Production by Different Microalgae Strains

Microalgae are able to produce many valuable biomolecules, such as polysaccharides, that presents a large diversity of biochemical structures and functions as antioxidant, antifungal, anticancer, among others. Static magnetic fields (SMF) influence the metabolism of microorganisms and has been shown as an alternative to increase microalgae biomass, yield and compounds production. Especially, some studies have highlighted that SMF application could enhance carbohydrate content. This study aimed to evaluate different conditions of SMF on Spirulina and Chlorella in indoor and outdoor conditions, in order to confirm the influence of SMF on polysaccharides production, evaluating which polysaccharidic fraction could be enhanced by SMF and highlighting a possible modification in EPS composition. Starch from Chlorella and exopolysaccharides (EPS) from Spirulina were quantified and characterized. SMF increased the starch content in Chorella fusca biomass. EPS productions from A. platensis and Spirulina sp. were not significantly increased, and global composition appeared similar to the controls (constituted basically of 80–86% neutral sugars and 13–19% uronic acids). However, the monosaccharide composition analysis revealed a significant modification of composition, i.e., the amount of fucose, arabinose, rhamnose, galactose and glucuronic acid was increased, while the glucose content was decreased. SMF application led to significant modification of polysaccharides production and this study demonstrate that combining the outdoor conditions with SMF, the starch content and EPS composition was positively affected.

Interaction of dough acidity and microalga level on bread quality and antioxidant properties

Microalgae nutritional and healthy dietary pattern might be affected by processes like breadmaking when used as ingredient. This study aims to determine the role of dough acidification on the nutritional pattern of Chlorella vulgaris enriched breads. Different levels of microalga (1%, 2% and 3%) were incorporated in the recipe in the presence of either 10% sourdough or chemically acidified doughs. Dough and bread characteristics were evaluated. Addition of microalga reduced the slice area and increased the crumb hardness, but it could be counteracted by increasing dough hydration and adapting proofing time. Doughs and breads enriched with microalga had green color. Dough acidification led to softer breads and enhanced the antioxidant activity of enriched breads. Microalgae incorporation increased the protein and ash content of the breads. Microalgae enriched breads made with chemically acidified doughs or sourdoughs had higher Total Phenolic Content and antioxidant activity as assessed by FRAP and ABTS methods.

Chlorella vulgaris α-L-arabino-α-L-rhamno-α,β-D-galactan structure and mechanisms of its anti-inflammatory and anti-remodelling effects

Microalgal exopolysaccharides (EPSs) are given great attention due to their potential biotechnology applications. Purified C. vulgaris EPS was subjected to compositional and sugar linkage analyses, and partial acid hydrolysis. Hydrolysate separation by gel chromatography afforded oligosaccharide fractions. Both, EPS and oligomers were studied by NMR spectroscopy. Data suggest very complex highly branched α-L-arabino-α-L-rhamno-α,β-D-galactan structure. Backbone repeating unit is formed by →2)-α-L-Rha (1 → 3)-α-L-Rha(1 → sequence, highly branched by long 1,6-linked α-D-Galp side chains, further branched at C2, C3 or C4 by α-L-Araf, α-D-Galf and β-D-Galf residues. α-L-Araf form longer 1,2-linked chains branched at C3, C4 or C5. Galf residues are localized as terminal units predominantly in the β configuration, while α-D-Galp and α-L-Araf may be partially O-methylated. Ex vivo biological assays showed increased interleukin-12 (IL-12) and interferon-gamma (INF-γ) levels corresponding to transforming growth factor beta (TGF-β) decrease in guinea pig model experimental asthma. These facts point to the anti-remodelling effect of Chlorella EPS and suggest its possible application in the treatment of asthma and chronic obstructive pulmonary disorder.