Safety and quality of the green tide algal species Ulva prolifera for option of human consumption: A nutrition and contamination study

The survival, gene expression, and DNA methylation of Paralichthys olivaceus impacted by the decay of green tide and bacterial infection in both laboratory and field simulation experiments

The recurring appearance of Ulva prolifera green tides has become a pressing environmental issue, especially for marine transportation, tourism, and aquaculture in the stage of decomposition. An abundance of decaying U. prolifera leads to water acidification, hypoxia and pathogenic microorganism proliferation, threatening marine germplasm resources, particularly benthic organisms with weak escape ability. Epigenetic modification is considered to be one of the molecular mechanisms involved in the plastic adaptive response to environmental changes. However, few studies concerning the specific impact of decaying green tide on benthic animals at the epigenetic level. In this study, decomposing algal effluents of U. prolifera, sediments containing uncorrupted U. prolifera, pathogenic microorganism were considered as impact factors, to reveal the effect of decaying U. prolifera on marine economic benthic species, Paralichthys olivaceus, using both field and laboratory simulation experiments. Field simulation experiment showed higher mortality rates and serious histopathological damage than the laboratory simulation experiment. And both the decaying U. prolifera and the sediment containing U. prolifera were harmful to P. olivaceus. Genome-wide DNA methylation and transcription correlation analyses showed that the response of P. olivaceus to green tide stress and bacterial infection was mainly mediated by immune signaling pathways such as PI3K-Akt signaling pathway. DNA methylation regulates the expression of immune-related genes involved in the PI3K-Akt signaling pathway, which enables P. olivaceus to adapt to the adverse environmental stresses by resisting apoptosis. In summary, this research analyzed the potential role of P. olivaceus in decaying U. prolifera, which is of great significance for understanding the impact of decaying green tide on marine commercial fish and also provides some theoretical guidance for the proliferation and release of fish seedlings.

An overview on the nutritional and bioactive components of green seaweeds

Green seaweed, as the most abundant species of macroseaweeds, is an important marine biological resource. It is a rich source of several amino acids, fatty acids, and dietary fibers, as well as polysaccharides, polyphenols, pigments, and other active substances, which have crucial roles in various biological processes such as antioxidant activity, immunoregulation, and anti-inflammatory response. In recent years, attention to marine resources has accelerated the exploration and utilization of green seaweeds for greater economic value. This paper elaborates on the main nutrients and active substances present in different green seaweeds and provides a review of their biological activities and their applications for high-value utilization.

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Pros and cons of Ulva lactuca and Cladophora glomerata grown in freshwater as feed

The use of algae as alternative feeds has long time attracted interest. However, due to excessive accumulation and variation in some of its components, difficulty in harvesting, and the need for some processes (cleaning, rinsing, drying, etc.) before final use, it causes hesitations about their use as feed. The feed values of Ulva lactuca and Cladophora glomerata collected from the same region in two different years (2020-2021) were investigated. The comparison of Ulva lactuca and Clodophora glomerata in two successive yearsyielded significant differences (P < 0.05) for crude protein% (22.23-10.78 and 18.38-12.85), crude ash% (19.28-34.10 and 40.67-35.51), ADF% (13.41-12.39 and 19.61-22.13), NDF% (39.18-36.35 and 29.36-35.74), calcium% (11.75-1.49 and 38.47-1.35), magnesium% (1.02-13.54 and 1.76-8.61), potassium% (0.53-6.17 and 1.50-17.86), sulphur% (4.76-2.41 and 3.41-1.80), and nickel ppm (9.50-87.5 and 20.25-105.3). Significant differences were also detected between other nutrients, minerals, energy, and digestibility values (P < 0.05). It has been determined that some heavy metal and mineral amounts are at restrictive levels at the point of use as feed. Aluminum (4982.7-7459.3 ppm) and silicon (8882.3-1449.3 ppm) were found in Ulva lactuca and Cladophora glomerata, respectively (P < 0.05). Sulphur, aluminum, silicon, and nickel amounts are above the tolarable feed criteria limits. Cadmium and lead were determined to be above the limits allowed in the legal legislation. Their biosorbent properties cause them to be affected by the ecosystem, and undesirable accumulations appear as a restrictive situation. Therefore, it is necessary to systematically determine their contents and variations. It was concluded that they are important in terms of potential feed value but should be used in a controlled manner.

Green Tides Significantly Alter the Molecular Composition and Properties of Coastal DOC and Perform Dissolved Carbon Sequestration

Despite green tides (or macroalgal blooms) having multiple negative effects, it is thought that they have a positive effect on carbon sequestration, although this aspect is rarely studied. Here, during the world's largest green tide (caused by Ulva prolifera) in the Yellow Sea, the concentration of dissolved organic carbon (DOC) increased by 20-37% in intensive macroalgal areas, and thousands of new molecular formulas rich in CHNO and CHOS were introduced. The DOC molecular species derived from U. prolifera constituted ∼18% of the total DOC molecular species in the seawater of bloom area, indicating the profound effect that green tides have on shaping coastal DOC. In addition, 46% of the macroalgae-derived DOC was labile DOC (LDOC), which had only a short residence time due to rapid microbial utilization. The remaining 54% was recalcitrant DOC (RDOC) rich in humic-like substances, polycyclic aromatics, and highly aromatic compounds that resisted microbial degradation and therefore have the potential to play a role in long-term carbon sequestration. Notably, source analysis showed that in addition to the microbial carbon pump, macroalgae are also an important source of RDOC. The number of RDOC molecular species contributed by macroalgae even exceed (77 vs 23%) that contributed by microorganisms.

Algae: Study of Edible and Biologically Active Fractions, Their Properties and Applications

The beneficial properties of algae make them perfect functional ingredients for food products. Algae have a high energy value and are a source of biologically active substances, proteins, fats, carbohydrates, vitamins, and macro- and microelements. They are also rich in polyunsaturated fatty acids, proteins, mycosporine-like amino acids, polysaccharides, polyphenols, carotenoids, sterols, steroids, lectins, halogenated compounds, polyketides, alkaloids, and carrageenans. Different extraction parameters are used depending on the purpose and the substances to be isolated. In this study, the following parameters were used: hydromodule 1:10 and an extraction duration of 1-2 h at the extraction temperature of 25-40 °C. A 30-50% solution of ethanol in water was used as an extractant. Algae extracts can be considered as potential natural sources of biologically active compounds with antimicrobial activity and antiviral properties. The content of crude protein, crude fat, and carbohydrates in U. Prolifera, C. racemosa var. peltata (Chlorophyta), S. oligocystum and S. fusiforme (SF-1) was studied. It was found that C. muelleri (Bacillariophyta), I. galbana (Haptophyta), and T. weissflogii (Bacillariophyta) contain about 1.9 times more omega-3 than omega-6 fatty acids. N. gaditana (Ochrophyta), D. salina (Chlorophyta), P. tricornutum (Bacillaryophyta) and I. galbana (Haptophyta) extracts showed inhibitory activity of varying intensities against E. coli or P. aeruginosa. In addition, algae and algae-derived compounds have been proposed to offer attractive possibilities in the food industry, especially in the meat sector, to evolve functional foods with myriad functionalities. Algae can increase the biological activity of food products, while the further study of the structure of compounds found in algae can broaden their future application possibilities.

Optimization of liquid fertilizer production from waste seaweed: A design of experiment based statistical approach

In Istanbul, which is surrounded by the sea on 3 sides, thousands of tons of seaweed that have formed naturally every year are washed ashore. In this study, the usability of these seaweeds which are landfilling already in fertilizer production was discussed. Liquid fertilizer production was carried out using 3 different physical and 4 different biological methods, and the produced fertilizers were diluted in 5 different ratios (1%, 10%, 25%, 50%, and 100%) and applied to cress seed. The effect of each fertilizer and its concentration on seed germination, plant length, number of leaves, and soil moisture-holding capacity was studied. The data obtained were analyzed using Response Surface Methodology (RSM). The results showed that if seaweed was fermented with anaerobic seed sludge for 15 days and applied to the plant by diluting it to 15-25%, plant growth will be supported at an optimum level. It has also been shown that if the seaweed was fermented with yeast culture for 18 days and fed with a concentration of >90%, the moisture-holding capacity of the soil could be increased by up to 27%.

Extraction Techniques, Biological Activities and Health Benefits of Marine Algae Enteromorpha prolifera Polysaccharide

There is increasing interest in the use of marine algae as functional food additives for improving human health. Enteromorpha (Ulva) prolifera (E. prolifera) is a seaweed green alga (Chlorophyta) that contains many bioactive compounds, of which polysaccharide is the main component. With the advancement of technology in the methods of extraction and analysis, recent studies in in vitro and animals model showed that polysaccharides derived from E. prolifera exert various biological activities, such as gut microbiota modulation, immunomodulation, antioxidant, antidiabetic, antimicrobial, and hypolipidemic. Research evidence has shown that methods of extraction and molecular modification, such as degradation, carboxymethylation, and sulfonation could alter the biological activities of polysaccharides. Therefore, in this review, we discussed the different extraction techniques, structural-activity relationship, and health benefits of sulfated polysaccharides derived from E. prolifera, and suggested future research avenues. This review helps to advance the extraction techniques and promote the application of marine algae polysaccharides as functional food and therapeutic agent.

Seaweeds as a “Palatable” Challenge between Innovation and Sustainability: A Systematic Review of Food Safety

Moderate or severe food insecurity affect 2 billion people worldwide. The four pillars of food security (availability, access, use and stability) are in danger due to the impact of climatic and anthropogenic factors which impact on the food system. Novel foods, like seaweeds, have the potential to increase food yields so that to contribute in preventing or avoiding future global food shortages. The purpose of this systematic review was to assess microbiological, chemical, physical, and allergenic risks associated with seaweed consumption. Four research strings have been used to search for these risks. Preferred Reporting Item for Systematic Reviews and Meta-analysis (PRISMA) guidelines were applied. Finally, 39 articles met the selected criteria. No significant hazards for microbiological, allergenic, and physical risks were detected. Regarding chemical risk, algae can accumulate various heavy metals, especially when harvested in polluted sites. Cultivating seaweeds in a controlled environment allows to avoid this risk. Periodic checks will be necessary on the finished products to monitor heavy metals levels. Since the consumption of algae seems to be on the rise everywhere, it seems to be urgent that food control authorities establish the safety levels to which eating algae does not represent any risk for human health.

Effect of aluminum stress on the quality of Enteromorpha prolifera based on SEM-EDX and FT-IR

To clarify the effect of aluminum stress on the quality of Enteromorpha prolifera (E. prolifera) and to explore the mechanism of the combination of aluminum and E. prolifera, we analyzed changes in the nutrients, micromorphology, element distribution, and spectrum of E. prolifera treated with different concentrations of aluminum (0, 0.2, 2.0, and 20.0 μmol·L–1) using scanning electron microscopy-energy dispersive spectroscopy (SEM-EDX) and Fourier-transform infrared spectroscopy (FT-IR). The biomass, protein, dietary fiber, and ash contents of E. prolifera initially increased and then subsequently decreased with an increasing concentration of aluminum. Meanwhile, the total amount of amino acids decreased. Scanning the surface of E. prolifera by SEM-EDX revealed that a high concentration of aluminum damaged the cells of E. prolifera. Additionally, the content of aluminum on the surface of E. prolifera cells increased and the absorption of other elements was also affected. The FT-IR analysis showed that aluminum might combine with the functional groups at the 3408 cm–1, 2928 cm–1, and 1072 cm–1 peaks in E. prolifera and alter the characteristic of the different absorption peaks.

Analysis of the interannual variation characteristics of the northernmost drift position of the green tide in the Yellow Sea

The green tide in the Yellow Sea is the world's largest macroalgal bloom. The maximum area affected by green tide can reach tens of thousands of square kilometers. Previous studies have shown that green tide drifts northward during the outbreak, yet the location of its northernmost drift and the characteristics of interannual variations have not been explored in detail. In this paper, we use the Moderate Resolution Imaging Spectrometer (MODIS) data, GaoFen-1 (GF-1) satellite data, unmanned aerial vehicle (UAV) aerial data, and field trips for extraction and monitoring of green tide and then analyze the emergence, development, and dissipation of the green tide in Rongcheng coastal waters and the change of the northernmost drift position and its related factors from the year of 2013 to 2018. The results show that green tide have drifted to the Rongcheng coastal area over the years and the northernmost drift position can reach 37.662° N in 2014. Interannual difference of the northernmost position of the drift of the green tide is obvious, it is mainly affected by the wind, and there is no certain connection with the maximum coverage area, the coverage area when reaching the northernmost position, and the existence days of the green tide. These results can help to understand the drift range and dissipation process of green tide in the Yellow Sea.

Chemical profiling of the Arctic sea lettuce Ulva lactuca (Chlorophyta) mass-cultivated on land under controlled conditions for food applications

The increasing use of seaweeds in European cuisine led to cultivation initiatives funded by the European Union. Ulva lactuca, commonly known as sea lettuce, is a fast growing seaweed in the North Atlantic that chefs are bringing into the local cuisine. Here, different strains of Arctic U. lactuca were mass-cultivated under controlled conditions for up to 10 months. We quantified various chemical constituents associated with both health benefits (carbohydrates, protein, fatty acids, minerals) and health risks (heavy metals). Chemical analyses showed that long-term cultivation provided biomass of consistently high food quality and nutritional value. Concentrations of macroelements (C, N, P, Ca, Na, K, Mg) and micronutrients (Fe, Zn, Co, Mn, I) were sufficient to contribute to daily dietary mineral intake. Heavy metals (As, Cd, Hg and Pb) were found at low levels to pose health risk. The nutritional value of Ulva in terms of carbohydrates, protein and fatty acids is comparable to some selected fruits, vegetables, nuts and grains.

Ulva lactuca, A Source of Troubles and Potential Riches

Ulva lactuca is a green macro alga involved in devastating green tides observed worldwide. These green tides or blooms are a consequence of human activities. Ulva blooms occur mainly in shallow waters and the decomposition of this alga can produce dangerous vapors. Ulva lactuca is a species usually resembling lettuce, but genetic analyses demonstrated that other green algae with tubular phenotypes were U. lactuca clades although previously described as different species or even genera. The capacity for U. lactuca to adopt different phenotypes can be due to environment parameters, such as the degree of water salinity or symbiosis with bacteria. No efficient ways have been discovered to control these green tides, but the Mediterranean seas appear to be protected from blooms, which disappear rapidly in springtime. Ulva contains commercially valuable components, such as bioactive compounds, food or biofuel. The biomass due to this alga collected on beaches every year is beginning to be valorized to produce valuable compounds. This review describes different processes and strategies developed to extract these different valuable components.