Anti-proliferative activity and chemical characterization by comprehensive two-dimensional liquid chromatography coupled to mass spectrometry of phlorotannins from the brown macroalga Sargassum muticum collected on North-Atlantic coasts

Seaweed-derived phenolic compounds as diverse bioactive molecules: A review on identification, application, extraction and purification strategies

Seaweed, a diverse group of marine macroalgae, has emerged as a rich source of bioactive compounds with numerous health-promoting properties. Among these, phenolic compounds have garnered significant attention for their diverse therapeutic applications. This review examines the methodologies employed in the extraction and purification of phenolic compounds from seaweed, emphasizing their importance in unlocking the full potential of these oceanic treasures. The article provides a comprehensive overview of the structural diversity and biological activities of seaweed-derived phenolics, elucidating their antioxidant, anti-inflammatory, and anticancer properties. Furthermore, it explores the impact of extraction techniques, including conventional methods and modern green technologies, on the yield and quality of phenolic extracts. The purification strategies for isolating specific phenolic compounds are also discussed, shedding light on the challenges and advancements in this field. Additionally, the review highlights the potential applications of seaweed-derived phenolics in various industries, such as pharmaceuticals, cosmetics, and functional foods, underscoring the economic value of these compounds. Finally, future perspectives and research directions are proposed to encourage continued exploration of seaweed phenolics, fostering a deeper understanding of their therapeutic potential and promoting sustainable practices in the extraction and purification processes. This comprehensive review serves as a valuable resource for researchers, industry professionals, and policymakers interested in harnessing the untapped potential of phenolic compounds from seaweed for the betterment of human health and environmental sustainability.

Antioxidant and anti-hepatitis A virus activities of Ecklonia cava Kjellman extracts

Ecklonia cava is a nutrient-rich algae species that contains abundant physiological phytochemicals, including peptides, carotenoids, fucoidans, and phlorotannins. However, elucidation of the antiviral effects of this algae and identification of new functional ingredients warrant further investigation. This study was aimed at investigating the potential anti-hepatitis A virus activities of extracts of E. cava prepared in different solvents. E. cava extracts were prepared using hot water and 70 % ethanol. The antioxidant activities of the extracts were confirmed by analyzing the total phenolic content, as well as 2,2-diphenyl-1-picrylhydrazyl and 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid radical scavenging activities. The inhibitory effects of the extracts against hepatitis A virus were analyzed using real-time polymerase chain reaction. The E. cava extract yield was 22.5-27.2 % depending on the extraction solvent. The 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity was 70.44 % and 91.05 % for hot water and ethanol extracts at a concentration of 1000 ppm. The 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid radical scavenging activity of the ethanol extract was the highest (93.57 %) at 1000 μg/mL. Fourier-transform infrared was used to identify the functional groups (phlorotannin and alginate) in the extraction solvents. Ultra-high performance liquid chromatography with quadrupole time-of-flight tandem mass spectrometry analysis revealed a potential bioactive compound previously unidentified in E. cava. Finally, we identified the antiviral activity of E. cava extracts against hepatitis A virus replication. These findings demonstrate that E. cava could be used as an anti-hepatitis A virus functional food and biological material.

From Ocean to Medicine: Harnessing Seaweed's Potential for Drug Development

Seaweed, a miscellaneous group of marine algae, has long been recognized for its rich nutritional composition and bioactive compounds, being considered nutraceutical ingredient. This revision delves into the promising role of seaweed-derived nutrients as a beneficial resource for drug discovery and innovative product development. Seaweeds are abundant sources of essential vitamins, minerals, polysaccharides, polyphenols, and unique secondary metabolites, which reveal a wide range of biological activities. These bioactive compounds possess potential therapeutic properties, making them intriguing candidates for drug leads in various medical applications and pharmaceutical drug development. It explores their pharmacological properties, including antioxidant, anti-inflammatory, antimicrobial, and anticancer activities, shedding light on their potential as therapeutic agents. Moreover, the manuscript provides insights into the development of formulation strategies and delivery systems to enhance the bioavailability and stability of seaweed-derived compounds. The manuscript also discusses the challenges and opportunities associated with the integration of seaweed-based nutrients into the pharmaceutical and nutraceutical industries. Regulatory considerations, sustainability, and scalability of sustainable seaweed sourcing and cultivation methods are addressed, emphasizing the need for a holistic approach in harnessing seaweed's potential. This revision underscores the immense potential of seaweed-derived compounds as a valuable reservoir for drug leads and product development. By bridging the gap between marine biology, pharmacology, and product formulation, this research contributes to the critical advancement of sustainable and innovative solutions in the pharmaceutical and nutraceutical sectors.

Investigation of the Potential Phlorotannins and Mechanism of Six Brown Algae in Treating Type II Diabetes Mellitus Based on Biological Activity, UPLC-QE-MS/MS, and Network Pharmacology

Type 2 diabetes mellitus (T2DM) has developed into an important health concern worldwide. The discovery of phlorotannins and their efficacy in the treatment of T2DM has become a hotspot for research in various fields. In this study, the potential phlorotannins and mechanism of six brown algae against T2DM were in-depth investigated using biological activity assays, LC-MS, and network pharmacology. First, the ethyl acetate fraction (EA frac.) showed high polyphenolic content and possessed significantly antioxidant and enzyme inhibitory abilities. Further, a total of fifty-nine peaks were obtained from six EA fracs. via UPLC-QE-MS/MS analysis, and fifteen of them were identified as phlorotannins and their isomers or derivatives. In detail, the chemical structures of six phlorotannins were inferred as dibenzodioxine-1,3,6,8-tetraol, bifuhalol, dioxinodehydroeckol, eckol, fucofurodiphlorethol, and fucotriphlorethol; three phlorotannin isomers were deduced to be fucophlorethol, trifucol, triphlorethol A, or triphlorethol B; and the phlorotannin derivative of m/z 263 was determined to be dibenzodioxine-1,2,3,6,8-pentanol or dibenzodioxine-1,2,4,5,7-pentanol. Moreover, 43 T2DM-related targets acted on by these chemicals were identified, and the function of phlorotannin to prevent and treat T2DM was elucidated in a holistic way based on the established compound-target-disease network, and GO function and KEGG pathway enrichment analysis.

Brown algae and their multiple applications as functional ingredient in food production

Brown algae are considered one of the resources that can contribute to transforming our global food system by promoting healthier diets and reducing environmental impact. In this sense, this review article aims to provide up-to-date information on the nutritional and functional improvement of brown algae when they are applied to different food matrices. Brown algae present sulfated polysaccharides (alginates, fucoidans, and laminarins), proteins, minerals, vitamins, dietary fibers, fatty acids, pigments, and bioactive compounds that can positively contribute to the development of highly nutritious food products, as well as used reformulate products already existing, to remove, reduce, increase, add and/or replace different components and obtain products that confer health-promoting properties. This review demonstrates that there is a tendency to use seaweed for the production of functional foods and that the number of commercially produced products from seaweed is increasing, that is, seaweed is a sector whose global market is expanding.

Antioxidant and chemotherapeutic efficacies of seaweed-derived phlorotannins in cancer treatment: A review regarding novel anticancer drugs

The ineffectiveness of traditional cancer therapies due to drug resistance, nontargeted delivery, and chemotherapy-associated adverse side effects has shifted attention to bioactive phytochemicals. Consequently, research efforts toward screening and identification of natural compounds with anticancer properties have increased in recent years. Marine seaweed-derived bioactive compounds, such as polyphenolic compounds, have exhibited anticancer properties. Phlorotannins (PTs), a major group of seaweed-derived polyphenolic compounds, have emerged as powerful chemopreventive and chemoprotective compounds, regulating apoptotic cell death pathways both in vitro and in vivo. In this context, this review focuses on the anticancer activity of polyphenols isolated from brown algae, with a special reference to PTs. Furthermore, we highlight the antioxidant effects of PTs and discuss how they can impact cell survival and tumor development and progression. Moreover, we discussed the potential therapeutic application of PTs as anticancer agents, having molecular mechanisms involving oxidative stress reduction. We have also discussed patents or patent applications that apply PTs as major components of antioxidant and antitumor products. With this review, researcher may gain new insights into the potential novel role of PTs, as well as uncover a novel cancer-prevention mechanism and improve human health.

Optimization of Extraction of Phlorotannins from the Arctic Fucus vesiculosus Using Natural Deep Eutectic Solvents and Their HPLC Profiling with Tandem High-Resolution Mass Spectrometry

Phlorotannins are secondary metabolites produced mainly by brown seaweeds (Phaeophyceae) and belong to the class of polyphenolic compounds with diverse bioactivities. The key factors in the extraction of polyphenols are the selection of a suitable solvent, method of extraction and selection of optimal conditions. Ultrasonic-assisted extraction (UAE) is one of the advanced energy-saving methods suitable for the extraction of labile compounds. Methanol, acetone, ethanol and ethyl acetate are the most commonly used solvents for polyphenol extraction. As alternatives to toxic organic solvents, a new class of green solvents, natural deep eutectic solvents (NADES), has been proposed for the efficient extraction of a wide range of natural compounds including polyphenols. Several NADES were screened previously for the extraction of phlorotannins; however, the extraction conditions were not optimized and chemical profiling of NADES extract was not performed. The purpose of this work was to study the effect of selected extraction parameters on the phlorotannin content in NADES extract from Fucus vesiculosus, optimization of extraction conditions and chemical profiling of phlorotannins in the NADES extract. A fast and green NADES-UAE procedure was developed for the extraction of phlorotannins. Optimization was performed through an experimental design and showed that NADES (lactic acid:choline chloride; 3:1) provides a high yield (137.3 mg phloroglucinol equivalents per g dry weight of algae) of phlorotannins under the following extraction conditions: extraction time 23 min, 30.0% water concentration and 1:12 sample to solvent ratio. The antioxidant activity of the optimized NADES extract was equal to that of EtOH extract. In total, 32 phlorotannins have been identified (one trimer, two tetramers, six pentamers, four hexamers, six heptamers, six octamers and seven nonamers) in NADES extracts from arctic F. vesiculosus using the HPLC-HRMS and MS/MS technique. It was noted that all the above-mentioned phlorotannins were identified in both EtOH and NADES extracts. Our results suggest that NADES could be considered as an alternative to the conventional techniques for the effective extraction of phlorotannins from F. vesiculosus with high antioxidant potential.

Applications of Antioxidant Secondary Metabolites of Sargassum spp

Sargassum is one of the largest and most diverse genus of brown seaweeds, comprising of around 400 taxonomically accepted species. Many species of this genus have long been a part of human culture with applications as food, feed, and remedies in folk medicine. Apart from their high nutritional value, these seaweeds are also a well-known reservoir of natural antioxidant compounds of great interest, including polyphenols, carotenoids, meroterpenoids, phytosterols, and several others. Such compounds provide a valuable contribution to innovation that can translate, for instance, into the development of new ingredients for preventing product deterioration, particularly in food products, cosmetics or biostimulants to boost crops production and tolerance to abiotic stress. This manuscript revises the chemical composition of Sargassum seaweeds, highlighting their antioxidant secondary metabolites, their mechanism of action, and multiple applications in fields, including agriculture, food, and health.

A macroporous resin purification process to obtain food-grade phlorotannin-rich extracts with α-glucosidase inhibitory activity from Chilean brown seaweeds: An UHPLC-MSn profiling

An efficient macroporous resin purification process was designed to obtain food-grade phlorotannin-rich extracts from the seaweeds Durvillaea incurvata and Lessonia spicata. Phlorotannins were profiled to relate structures with the α-glucosidase inhibitory activity of the extracts. Liquid chromatography-mass spectrometry was applied for tentative identification. The best phlorotannin purification performance was achieved with HP-20 resin and elution with 80% v/v ethanol. This is the first study that demonstrates the effectivity of HP-20 resin for removing potentially toxic elements (As, Cd) from seaweed extracts. Fucols/phlorethols/fucophlorethols isomers up to 4 phloroglucinol units (PGU) were the most representative phlorotannins. High molecular weight species (11-21 PGU), although in low abundances, were detected in D. incurvata for the first time. Eckols, carmalols, fuhalols, phenolic acids, and flavonoids were also detected. Some extracts' potent α-glucosidase inhibitory activities were related to their high phlorotannin abundances, the presence of phlorotannins of a high degree of polymerization, and the phlorotannins class.

Seaweed for climate mitigation, wastewater treatment, bioenergy, bioplastic, biochar, food, pharmaceuticals, and cosmetics: a review

The development and recycling of biomass production can partly solve issues of energy, climate change, population growth, food and feed shortages, and environmental pollution. For instance, the use of seaweeds as feedstocks can reduce our reliance on fossil fuel resources, ensure the synthesis of cost-effective and eco-friendly products and biofuels, and develop sustainable biorefinery processes. Nonetheless, seaweeds use in several biorefineries is still in the infancy stage compared to terrestrial plants-based lignocellulosic biomass. Therefore, here we review seaweed biorefineries with focus on seaweed production, economical benefits, and seaweed use as feedstock for anaerobic digestion, biochar, bioplastics, crop health, food, livestock feed, pharmaceuticals and cosmetics. Globally, seaweeds could sequester between 61 and 268 megatonnes of carbon per year, with an average of 173 megatonnes. Nearly 90% of carbon is sequestered by exporting biomass to deep water, while the remaining 10% is buried in coastal sediments. 500 gigatonnes of seaweeds could replace nearly 40% of the current soy protein production. Seaweeds contain valuable bioactive molecules that could be applied as antimicrobial, antioxidant, antiviral, antifungal, anticancer, contraceptive, anti-inflammatory, anti-coagulants, and in other cosmetics and skincare products.

Two-dimensional chromatography in screening of bioactive components from natural products

INTRODUCTION

Screening and analysis of bioactive components from natural products is a fundamental part of new drug development and innovation. Two-dimensional (2D) chromatography has been demonstrated to be an effective method for screening and preparation of specific bioactive components from complex natural products.

OBJECTIVE

To collect details of application of 2D chromatography in screening of natural product bioactive components and to outline the research progress of different separation mechanisms and strategies.

METHODOLOGY

Three screening strategies based on 2D chromatography are reviewed, including traditional separation-based screening, bioactivity-guided screening and affinity chromatography-based screening. Meanwhile, in order to cover these aspects, selections of different separation mechanisms and modes are also presented.

RESULTS

Compared with traditional one-dimensional (1D) chromatography, 2D chromatography has unique advantages in terms of peak capacity and resolution, and it is more effective for screening and identifying bioactive components of complex natural products.

CONCLUSION

Screening of natural bioactive components using 2D chromatography helps separation and analysis of complex samples with greater targeting and relevance, which is very important for development of innovative drug leads.

Overview of Phlorotannins' Constituents in Fucales

Fucales are an order within the Phaeophyceae that include most of the common littoral seaweeds in temperate and subtropical coastal regions. Many species of this order have long been a part of human culture with applications as food, feedand remedies in folk medicine. Apart from their high nutritional value, these seaweeds are also a well-known reservoir of multiple bioactive compounds with great industrial interest. Among them, phlorotannins, a unique and diverse class of brown algae-exclusive phenolics, have gathered much attention during the last few years due to their numerous potential health benefits. However, due to their complex structural features, combined with the scarcity of standards, it poses a great challenge to the identification and characterization of these compounds, at least with the technology currently available. Nevertheless, much effort has been taken towards the elucidation of the structural features of phlorotannins, which have resulted in relevant insights into the chemistry of these compounds. In this context, this review addresses the major contributions and technological advances in the field of phlorotannins extraction and characterization, with a particular focus on Fucales.

Advancing quantification methods for polyphenols in brown seaweeds-applying a selective qNMR method compared with the TPC assay

INTRODUCTION

Brown seaweeds are a sustainable biomass with a potential for various industrial applications. Polyphenols are an important contributor to this potential.

OBJECTIVE

The aim was total quantification of polyphenols in brown seaweeds from different tidal zones, using a selective 1 H quantitative NMR (qNMR) method, comparing the results with the colorimetric Folin-Ciocalteu total phenolic content (TPC) assay.

METHOD

qNMR was performed with integration of selected peaks in the aromatic region (7-5.5 ppm). Deselection of non-polyphenolic 1 H signals was based on information from 2D (1 H-13 C, 1 H-15 N) NMR spectra. 13 C NMR phlorotannin characterisation facilitated the average number of protons expected to be found per aromatic ring used for the 1 H quantification.

RESULTS

Selective qNMR and the TPC assay showed similar results for the three sublittoral growing species from the Laminariaceae; lower amounts for Laminaria hyperborea and Laminaria digitata (qNMR: 0.4%-0.6%; TPC: 0.6%-0.8%, phloroglucinol equivalents (PGE), dry weight (DW)) and higher amounts for Saccharina latissima (qNMR: 1.2%; TPC: 1.5%, PGE, DW). For the eulittoral Fucaceae, Fucus vesiculosus (qNMR: 1.1%; TPC: 4.1%; PGE, DW) and Ascophyllum nodosum (qNMR: 0.9%; TPC: 2.0%; PGE, DW), the TPC results were found to be up to three times higher than the qNMR results. The 13 C NMR characterisation showed the highest phlorotannin polymerisation degree for F. vesiculosus.

CONCLUSION

The TPC assay provided similar polyphenolic amounts to the selective qNMR method for sublittoral species. For eulittoral growing species, the TPC method showed amounts up to three times higher than the qNMR method-most likely illustrating the lack of selectivity in the TPC assay.

Seaweed Phenolics as Natural Antioxidants, Aquafeed Additives, Veterinary Treatments and Cross-Linkers for Microencapsulation

Driven by consumer demand and government policies, synthetic additives in aquafeed require substitution with sustainable and natural alternatives. Seaweeds have been shown to be a sustainable marine source of novel bioactive phenolic compounds that can be used in food, animal and aqua feeds, or microencapsulation applications. For example, phlorotannins are a structurally unique polymeric phenolic group exclusively found in brown seaweed that act through multiple antioxidant mechanisms. Seaweed phenolics show high affinities for binding proteins via covalent and non-covalent bonds and can have specific bioactivities due to their structures and associated physicochemical properties. Their ability to act as protein cross-linkers means they can be used to enhance the rheological and mechanical properties of food-grade delivery systems, such as microencapsulation, which is a new area of investigation illustrating the versatility of seaweed phenolics. Here we review how seaweed phenolics can be used in a range of applications, with reference to their bioactivity and structural properties.

Phlorotannins of the Brown Algae Sargassum vulgare from the Mediterranean Sea Coast

Brown seaweeds are a good source of bioactive compounds, particularly of phlorotannins, which may exert a wide spectrum of pharmacological properties. In the present study, phlorotannins of S. vulgare were extracted using a 70% acetone solution and the crude extract was further purified through liquid–liquid partition, giving rise to n-hexane, ethyl acetate and aqueous residue fractions. The crude extract and the purified fractions were evaluated for potential antioxidant abilities as well as for inhibitory potential towards the digestive enzymes α-amylase and pancreatic lipase, and anti-inflammatory potential through the hindering of albumin denaturation. Overall, the ethyl acetate fraction was the richest in phlorotannins (9.4 ± 0.03 mg PGE/g) and was also the most promising regarding the tested bioactive properties. Of note, its inhibitory potential towards α-amylase was about nine times that of the commercial drug acarbose and its inhibitory activity against high temperature-induced protein denaturation was superior to that of the non-steroidal drug ketoprofen. According to UHPLC-DAD-ESI-MS/MS analysis, this fraction contained a range of phlorotannins with at least six units of phloroglucinol, including dibenzodioxine-1,3,6,8-tetraol, fuhalol, pentaphlorethol, fucopentaphlorethol and dihydroxypentafuhalol, in addition to several less common phlorotannin sulfate derivatives.

An Overview of Potential Seaweed-Derived Bioactive Compounds for Pharmaceutical Applications

Nowadays, seaweeds are widely involved in biotechnological applications. Due to the variety of bioactive compounds in their composition, species of phylum Ochrophyta, class Phaeophyceae, phylum Rhodophyta and Chlorophyta are valuable for the food, cosmetic, pharmaceutical and nutraceutical industries. Seaweeds have been consumed as whole food since ancient times and used to treat several diseases, even though the mechanisms of action were unknown. During the last decades, research has demonstrated that those unique compounds express beneficial properties for human health. Each compound has peculiar properties (e.g., antioxidant, antimicrobial, antiviral activities, etc.) that can be exploited to enhance human health. Seaweed’s extracted polysaccharides are already involved in the pharmaceutical industry, with the aim of replacing synthetic compounds with components of natural origin. This review aims at a better understanding of the recent uses of algae in drug development, with the scope of replacing synthetic compounds and the multiple biotechnological applications that make up seaweed’s potential in industrial companies. Further research is needed to better understand the mechanisms of action of seaweed’s compounds and to embrace the use of seaweeds in pharmaceutical companies and other applications, with the final scope being to produce sustainable and healthier products.

Marine algal flavonoids and phlorotannins; an intriguing frontier of biofunctional secondary metabolites

Algae are the oldest representatives of the plant world with reserves exceeding hundreds of millions of tons in the world's oceans. Currently, a growing interest is placed toward the use of algae as feedstocks for obtaining numerous natural products. Algae are a rich source of polyphenols that possess intriguing structural diversity. Among the algal polyphenols, phlorotannins, which are unique to brown seaweeds, and have immense value as potent modulators of biochemical processes linked to chronic diseases. In algae, flavonoids remain under-explored compared to other categories of polyphenols. Both phlorotannins and flavonoids are inclusive of compounds indicating a wide structural diversity. The present paper reviews the literature on the ecological significance, biosynthesis, structural diversity, and bioactivity of seaweed phlorotannins and flavonoids. The potential implementation of these chemical entities in functional foods, cosmeceuticals, medicaments, and as templates in drug design are described in detail, and perspectives are provided to tackle what are perceived to be the most momentous challenges related to the utilization of phlorotannins and flavonoids. Moving beyond: industrial biotechnology applications, metabolic engineering, total synthesis, biomimetic synthesis, and chemical derivatization of phlorotannins and flavonoids could broaden the research perspectives contributing to the health and economic up-gradation.

Phlorotannins-bioactivity and extraction perspectives

Phlorotannins, a seaweed based class of polyphenolic compounds, have proven to possess potential bioactivities such as antioxidant, antimicrobial, anti-allergic, anti-diabetic, anti-inflammatory, anti-cancerous, neuroprotection etc. These bioactivities have further increased demand globally and sustainable techniques such as supercritical fluid extraction, microwave assisted extraction, enzyme assisted extraction, extraction using deep eutectic solvents etc. are being explored currently for production of phlorotannin-rich extracts. In spite of such well documented bioactivities, very few phlorotannin-based nutraceuticals are available commercially which highlights the significance of generating consumer awareness about their physiological benefits. However, for industry level commercialization accurate quantification of phlorotannins with respect to the different classes is vital requiring sophisticated analytical techniques such as mass spectrometry, ¹H-NMR spectroscopy etc. owing to the wide structural diversity. This review summarizes the extraction and bioactivities of phlorotannins based on the findings of in vivo and in vitro studies.

Aquatic Phlorotannins and Human Health: Bioavailability, Toxicity, and Future Prospects

Medicinal chemists and pharmacognosists have relied on terrestrial sources for bioactive phytochemicals to manage and treat disease conditions. However, minimal interest is given to sea life, especially macroalgae and their inherent phytochemical reserves. Phlorotannins are a special class of phytochemicals mainly predominant in brown algae of marine and estuarine habitats. Phlorotannins are formed through the polymerization of phloroglucinol residues and derivatives via the polyketide (acetate–malonate) pathway. Studies over the past decades have implicated phlorotannins with several bioactivities, including anti-herbivory, antioxidants, anti-inflammatory, anti-microbial, anti-proliferative, anti-diabetic, radio-protective, adipogenic, anti-allergic, and anti-human immunodeficiency virus (anti-HIV) properties. All these activities are reflected in their applications as nutraceuticals and cosmeceutical agents. This article reviews the chemical composition of phlorotannins, their biological roles, and their applications. Moreover, very few studies on phlorotannin bioavailability, safety, and toxicity have been thoroughly reviewed. The paper concludes by suggesting exciting research questions for further studies.

Strategies to circumvent the solvent strength mismatch problem in online comprehensive two-dimensional liquid chromatography

On-line comprehensive two-dimensional liquid chromatography is a powerful technique for the separation of highly complex samples. Due to the addition of the second dimension of separation, impressive peak capacities can be obtained within a reasonable analysis time compared to one-dimensional liquid chromatography. In online comprehensive two-dimensional liquid chromatography, the separation power is maximized by selecting two separation dimensions as orthogonal as possible, which most often requires the combination of different mobile phases and stationary phases. The online transfer of a given solvent from the first dimension to the second dimension may cause severe injection effects in the second dimension, mostly due to solvent strength mismatch. Those injection effects may include peak broadening, peak distortion, peak splitting or breakthrough phenomenon. They are often found to reduce significantly the peak capacity and the peak intensity. To overcome such effects, arising specifically in online comprehensive two-dimensional liquid chromatography, different methods have been developed over the years. In this review, we focused on the most recently reported ones. A critical discussion, supported by a theoretical approach, gives an overview of their advantages and drawbacks.

Antitumor Activity of Fucus vesiculosus-Derived Phlorotannins through Activation of Apoptotic Signals in Gastric and Colorectal Tumor Cell Lines

Seaweeds are one of the largest producers of biomass in the marine environment and a source of multiple bioactive metabolites with valuable health benefits. Among these, phlorotannins have been widely recognized for their promising bioactive properties. The potential antitumor capacity of Fucus vesiculosus-derived phlorotannins remains, however, poorly explored, especially in gastrointestinal tract-related tumors. Therefore, this work aimed to evaluate the cytotoxic properties and possible mechanisms by which F. vesiculosus crude extract (CRD), phlorotannin-rich extract (EtOAc), and further phlorotannin-purified fractions (F1-F9) trigger cell death on different tumor cell lines of the gastrointestinal tract, using flow cytometry. The results indicate that F. vesiculosus samples exert specific cytotoxicity against tumor cell lines without affecting the viability of normal cells. Moreover, it was found that, among the nine different phlorotannin fractions tested, F5 was the most active against both Caco-2 colorectal and MKN-28 gastric cancer cells, inducing death via activation of both apoptosis and necrosis. The UHPLC-MS analysis of this fraction revealed, among others, the presence of a compound tentatively identified as eckstolonol and another as fucofurodiphlorethol, which could be mainly responsible for the promising cytotoxic effects observed in this sample. Overall, the results herein reported contribute to a better understanding of the mechanisms behind the antitumor properties of F. vesiculosus phlorotannin-rich extracts.

Pressurized Hot Liquid Extraction with 15% v/v Glycerol-Water as An Effective Environment-Friendly Process to Obtain Durvillaea incurvata and Lessonia spicata Phlorotannin Extracts with Antioxidant and Antihyperglycemic Potential

Brown seaweed phlorotannins have shown the potential to promote several health benefits. Durvillaea incurvata and Lessonia spicata-species that are widely distributed in central and southern Chile-were investigated to obtain phlorotannin extracts with antioxidant and antihyperglycemic potential. The use of an environmentally friendly and food-grade glycerol-based pressurized hot liquid extraction (PHLE) process (15% v/v glycerol water) was assessed for the first time to obtain phlorotannins. Multiple effects were analyzed, including the effect of the species, harvesting area (Las Cruces and Niebla), and anatomical part (holdfast, stipe, and frond) on the extracts' polyphenol content (TPC), antioxidant capacity (AC), and carbohydrate-hydrolyzing enzyme-α-glucosidase and α-amylase-inhibitory activity. Contaminants, such as mannitol, heavy metals (As, Cd, Pb, Hg, and Sn), and 5-hydroxymethylfurfural (HMF), were also determined. The anatomical part used demonstrated a significant impact on the extracts' TPC and AC, with holdfasts showing the highest values (TPC: 95 ± 24 mg phloroglucinol equivalents/g dry extract; DPPH: 400 ± 140 μmol Trolox equivalents/g dry extract; ORAC: 560 ± 130 μmol TE/g dry extract). Accordingly, holdfast extracts presented the most potent α-glucosidase inhibition, with D. incurvata from Niebla showing an activity equivalent to fifteen times that of acarbose. Only one frond and stipe extract showed significant α-glucosidase inhibitory capacity. No α-amylase inhibition was found in any extract. Although no HMF was detected, potentially hazardous cadmium levels (over the French limit) and substantial mannitol concentrations-reaching up to 50% of the extract dry weight-were found in most seaweed samples and extracts. Therefore, further purification steps are suggested if food or pharmaceutical applications are intended for the seaweed PHLE extracts obtained in this study.

Brown Algae Phlorotannins: A Marine Alternative to Break the Oxidative Stress, Inflammation and Cancer Network

According to the WHO, cancer was responsible for an estimated 9.6 million deaths in 2018, making it the second global leading cause of death. The main risk factors that lead to the development of this disease include poor behavioral and dietary habits, such as tobacco use, alcohol use and lack of fruit and vegetable intake, or physical inactivity. In turn, it is well known that polyphenols are deeply implicated with the lower rates of cancer in populations that consume high levels of plant derived foods. In this field, phlorotannins have been under the spotlight in recent years since they have shown exceptional bioactive properties, with great interest for application in food and pharmaceutical industries. Among their multiple bioactive properties, phlorotannins have revealed the capacity to interfere with several biochemical mechanisms that regulate oxidative stress, inflammation and tumorigenesis, which are central aspects in the pathogenesis of cancer. This versatility and ability to act either directly or indirectly at different stages and mechanisms of cancer growth make these compounds highly appealing for the development of new therapeutical strategies to address this world scourge. The present manuscript revises relevant studies focusing the effects of phlorotannins to counteract the oxidative stress-inflammation network, emphasizing their potential for application in cancer prevention and/or treatment.

Evaluation of Ultrasound, Microwave, Ultrasound-Microwave, Hydrothermal and High Pressure Assisted Extraction Technologies for the Recovery of Phytochemicals and Antioxidants from Brown Macroalgae

This study aims to explore novel extraction technologies (ultrasound-assisted extraction (UAE), microwave-assisted extraction (MAE), ultrasound-microwave-assisted extraction (UMAE), hydrothermal-assisted extraction (HAE) and high-pressure-assisted extraction (HPAE)) and extraction time post-treatment (0 and 24 h) for the recovery of phytochemicals and associated antioxidant properties from Fucus vesiculosus and Pelvetia canaliculata. When using fixed extraction conditions (solvent: 50% ethanol; extraction time: 10 min; algae/solvent ratio: 1/10) for all the novel technologies, UAE generated extracts with the highest phytochemical contents from both macroalgae. The highest yields of compounds extracted from F. vesiculosus using UAE were: total phenolic content (445.0 ± 4.6 mg gallic acid equivalents/g), total phlorotannin content (362.9 ± 3.7 mg phloroglucinol equivalents/g), total flavonoid content (286.3 ± 7.8 mg quercetin equivalents/g) and total tannin content (189.1 ± 4.4 mg catechin equivalents/g). In the case of the antioxidant activities, the highest DPPH activities were achieved by UAE and UMAE from both macroalgae, while no clear pattern was recorded in the case of FRAP activities. The highest DPPH scavenging activities (112.5 ± 0.7 mg trolox equivalents/g) and FRAP activities (284.8 ± 2.2 mg trolox equivalents/g) were achieved from F. vesiculosus. Following the extraction treatment, an additional storage post-extraction (24 h) did not improve the yields of phytochemicals or antioxidant properties of the extracts.

Antidiabetic and antioxidant activity of phlorotannins extracted from the brown seaweed Cystoseira compressa in streptozotocin-induced diabetic rats

Diabetes mellitus is considered a set of diseases that lead to high glucose level due to the absolute or relative absence of insulin. The study investigated the antioxidant activity and antidiabetic effect of phlorotannins extracted from brown seaweed Cystoseira compressa. Phlorotannins were extracted from C. compressa. It was confirmed by 2,4 dimethoxy benzaldehyde assay (DMBA), ultraviolet spectra, Fourier transform infrared spectroscopy, and ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The free radical scavenging activity of phlorotannins was estimated by total antioxidant capacity, 1,1-diphenyl-2-picrylhydrazyl radical-scavenging activity, and 2,2 azino-bis3-ethylbenthiazoline-6-sulfonic acid assays. Four groups of albino rats used in this study include control normal, control phlorotannins extract, diabetic by intraperitoneally administering of streptozotocin, and diabetic treatment with 60 mg/kg of phlorotannin extract after 4 weeks of diabetes induction. The main compound identified by UPLC-MS/MS in C. compressa extract belonged to the fuhalol. C. compressa extract showed high antioxidant properties. Phlorotannins significantly decreased serum glucose, liver malondialdehyde, and α-amylase, glucosidase activities. However, total antioxidant capacity, serum insulin, hepatic glutathione, and AMPKα2 expression in skeletal muscle were improved compared to the diabetic group. The histopathological examination showed that phlorotannins markedly reduced damage in β cells of pancreases. Phlorotannins from C. compressa have efficient antioxidant activity and the antidiabetic effect that may be utilized in human health.

Reversed phase versus hydrophilic interaction liquid chromatography as first dimension of comprehensive two-dimensional liquid chromatography systems for the elucidation of the polyphenolic content of food and natural products

Comprehensive two-dimensional liquid chromatography is a well-established method for the unraveling of very complex real-world samples. With regard to food and natural products such a technique turned out to be a very promising approach due to its high resolving power and improved identification capability, especially in combination with mass spectrometry. In this context, polyphenols comprise a particular complex class of bioactive compounds, due to their nature and content in commonly consumed foodstuffs, making their analysis challenging. The present contribution shows an overview of the two commonly employed approaches used for polyphenol analysis, viz. RP-LC × RP-LC and HILIC × RP-LC. Furthermore, the latest implementations as well as limitations and future perspectives are critically reported.

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.

A Biorefinery Approach to the Biomass of the Seaweed Undaria pinnatifida (Harvey Suringar, 1873): Obtaining Phlorotannins-Enriched Extracts for Wound Healing

Brown seaweeds are recognized sources of compounds with a wide range of properties and applications. Within these compounds, phlorotannins are known to possess several bioactivities (e.g., antioxidant, anti-inflammatory, and antimicrobial) with potential to improve wound healing. To obtain phlorotannins enriched extracts from Undaria pinnatifida, a biorefinery was set using low-cost industry-friendly methodologies, such as sequential solid-liquid extraction and liquid-liquid extraction. The obtained extracts were screened for their antioxidant and antimicrobial activity against five common wound pathogens and for their anti-inflammatory potential. The ethanolic wash fraction (wE100) had the highest antioxidant activity (114.61 ± 10.04 mmol·mg-1 extract by Diphenyl-1-picrylhydrazyl (DPPH) and 6.56 ± 1.13 mM eq. Fe II·mg-1 extract by and Ferric Reducing Antioxidant Power (FRAP)), acting efficiently against Gram-negative (Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus) bacteria, and showing a nitric oxide production inhibition over 47% when used at 0.01 µg·mL-1. NMR and FTIR chemical characterization suggested that phlorotannins are present. Obtained fraction wE100 proved to be a promising candidate for further inclusion as wound healing agents, while the remaining fractions analyzed are potential sources for other biotechnological applications, giving emphasis to a biorefinery and circular economy framework to add value to this seaweed and the industry.

Optimization of Microwave-Assisted Extraction of Phlorotannin From Sargassum swartzii (Turn.) C. Ag. With Ethanol/Water

Sargassum is a genus of brown macroalgae in the class Phaeophyta, distributed widely in all oceans, including those of Vietnam. Species of this genus have been proven to possess diverse biological activities, such as antioxidant, anti-fungal, and anti-inflammatory, along with many benefits and applications for human health, including anti-diabetic, obesity, and thrombosis. These benefits arise from a diverse chemical composition, with compounds such as fucoidan, mannitol, and especially phlorotannin—a group of phenolic derivatives found predominantly in brown algae. In this study, we evaluated and optimized the factors that affected the extraction process of phlorotannins from Sargassum swartzii (Turn.) C. Ag., a common species of brown macroalgae in Vietnam. The process utilized ethanol and water as the solvent system, and the extraction process was assisted with the use of microwaves. To carry out optimization studies, Response Surface Methodology (RSM) was adopted according to a Central Composite Desisgn (CCD), taking four processing factors into consideration, ethanol concentration (%, v/v), extraction time (minutes), solvent/material ratio (v/w), and microwave output power (W) as independent variables. Phlorotannin concentration (mgPhE/g) and extract mass (mg) were regarded as optimization outcomes. Experimental conditions that produced the highest phlorotannin yield from 10 g of S. swartzii are as follows: Extraction time of 65 minutes, ethanol concentration of 52%, microwave output power of 613 W, and solvent/material ratio of 33/1 (v/w). These conditions corresponded to a phlorotannin concentration of 5.59 ± 0.11 mg PhE/g, and a total extract content of 27.88 ± 0.13 mg/g.

Antiviral Effects of Polyphenols from Marine Algae

The disease-preventive and medicinal properties of plant polyphenolic compounds have long been known. As active ingredients, they are used to prevent and treat many noncommunicable diseases. In recent decades, marine macroalgae have attracted the attention of biotechnologists and pharmacologists as a promising and almost inexhaustible source of polyphenols. This heterogeneous group of compounds contains many biopolymers with unique structure and biological properties that exhibit high anti-infective activity. In the present review, the authors focus on the antiviral potential of polyphenolic compounds (phlorotannins) from marine algae and consider the mechanisms of their action as well as other biological properties of these compounds that have effects on the progress and outcome of viral infections. Effective nutraceuticals, to be potentially developed on the basis of algal polyphenols, can also be used in the complex therapy of viral diseases. It is necessary to extend in vivo studies on laboratory animals, which subsequently will allow proceeding to clinical tests. Polyphenolic compounds have a great potential as active ingredients to be used for the creation of new antiviral pharmaceutical substances.

Tannin polymerization: an overview

This review critically addresses the most relevant and innovative techniques for obtaining polymers from tannins.

Phlorotannins: From isolation and structural characterization, to the evaluation of their antidiabetic and anticancer potential

Phlorotannins are phenolic characteristic compounds of brown seaweeds that are only constituted by phloroglucinol (1,3,5-trihydroxybenzene). They are chain- and net-like structures of diverse molecular weights and have been widely identified in Ecklonia, Eisenia, and Ishige species. Since the time they were discovered in the '70 s, phlorotannins have been suggested as a main factor responsible for the antimicrobial activities attributed to algae extracts. Currently, cumulative in vitro and in vivo research evidence the diverse bioactivities of phlorotannin extracts -such as antidiabetic, anticancer, and antibacterial- pointing out their potential pharmacological and food applications. However, metabolomic studies and clinical trials are scarce, and thus many phlorotannins health-beneficial effects in humans are not yet confirmed. This article reviews recent studies assessing the antidiabetic and anticancer activities of phlorotannins. Particularly, their potential to prevent and control the progression of these non-communicable diseases is discussed, considering in vitro and animal studies, as well as clinical interventions. In contrast to other approaches, we only included investigations with isolated phlorotannins or phlorotannin-rich extracts. Thus, phlorotannin extraction, purification and characterization procedures are briefly addressed. Overall, although considerable research showing the antidiabetic and anticancer potential of phlorotannins is now available, further clinical trials are still necessary to conclusively demonstrate the efficacy of these compounds as adjuvants for diabetes and cancer prevention or treatment.

Bioactive Properties of Marine Phenolics

Phenolic compounds from marine organisms are far less studied than those from terrestrial sources since their structural diversity and variability require powerful analytical tools. However, both their biological relevance and potential properties make them an attractive group deserving increasing scientific interest. The use of efficient extraction and, in some cases, purification techniques can provide novel bioactives useful for food, nutraceutical, cosmeceutical and pharmaceutical applications. The bioactivity of marine phenolics is the consequence of their enzyme inhibitory effect and antimicrobial, antiviral, anticancer, antidiabetic, antioxidant, or anti-inflammatory activities. This review presents a survey of the major types of phenolic compounds found in marine sources, as well as their reputed effect in relation to the occurrence of dietary and lifestyle-related diseases, notably type 2 diabetes mellitus, obesity, metabolic syndrome, cancer and Alzheimer's disease. In addition, the influence of marine phenolics on gut microbiota and other pathologies is also addressed.

Macroalgae as a Source of Valuable Antimicrobial Compounds: Extraction and Applications

In the last few decades, attention on new natural antimicrobial compounds has arisen due to a change in consumer preferences and the increase in the number of resistant microorganisms. Macroalgae play a special role in the pursuit of new active molecules as they have been traditionally consumed and are known for their chemical and nutritional composition and their biological properties, including antimicrobial activity. Among the bioactive molecules of algae, proteins and peptides, polysaccharides, polyphenols, polyunsaturated fatty acids and pigments can be highlighted. However, for the complete obtaining and incorporation of these molecules, it is essential to achieve easy, profitable and sustainable recovery of these compounds. For this purpose, novel liquid-liquid and solid-liquid extraction techniques have been studied, such as supercritical, ultrasound, microwave, enzymatic, high pressure, accelerated solvent and intensity pulsed electric fields extraction techniques. Moreover, different applications have been proposed for these compounds, such as preservatives in the food or cosmetic industries, as antibiotics in the pharmaceutical industry, as antibiofilm, antifouling, coating in active packaging, prebiotics or in nanoparticles. This review presents the main antimicrobial potential of macroalgae, their specific bioactive compounds and novel green extraction technologies to efficiently extract them, with emphasis on the antibacterial and antifungal data and their applications.

Phlorotannins from Fucus vesiculosus: Modulation of Inflammatory Response by Blocking NF-κB Signaling Pathway

Due to their large spectrum of bioactive properties, much attention has recently been drawn to phlorotannins-i.e., phenolic compounds characteristic from brown macroalgae. This study aimed to evaluate the antioxidant and anti-inflammatory properties of F. vesiculosus phlorotannin extracts and purified fractions. Overall, the crude extract and its ethyl acetate fraction (EtOAc) showed good radical scavenging activity, particularly towards nitric oxide (NO•). Subsequent subfractions of EtOAc (F1 to F9) with different molecular weights were then shown to inhibit lipopolysaccharide-induced NO• production in macrophages, with stronger effects being observed for fractions of lower MWs. Of the three intracellular markers analyzed, inducible NO• synthase showed the highest sensitivity to almost all the phlorotannin-rich samples, followed by interleukin 1β and cyclooxygenase 2, which was only inhibited by F2. Furthermore, this subfraction inhibited the phosphorylation and degradation of inhibitory protein κBα, thus preventing the activation of NF-κB and blocking the inflammatory cascade at the transcriptional level. This sample was characterized by the presence of a major compound with a deprotonated molecular ion at m/z 507 with a fragmentation pattern coherent with that of a phlorotannin derivative. Overall, this work unveiled some of the mechanistic aspects behind the anti-inflammatory capacity of phlorotannins from F. vesiculosus, endorsing its use as a possible natural source of anti-inflammatory compounds.

Seaweed-based natural ingredients: Stability of phlorotannins during extraction, storage, passage through the gastrointestinal tract and potential incorporation into functional foods

Adding value to seaweed by extracting their different bioactive compounds and incorporating them into foods represent an interesting and strategic approach to diversify the functional foods offer. However, once harvested, fresh seaweed must overcome a sequence of crucial steps to confer their biological activity. Pre-processing operations and extraction processes, as well as long-term storage, play important roles in improving or decreasing the phlorotannins content. In their way to the gut (biological target), phlorotannins are exposed to the human gastrointestinal tract (GIT), where the physiological pH and digestive enzymes can significantly affect the phlorotannins' stability and thus, alter their biological activity. Besides, the subsequent incorporation into foodstuffs could be limited due to sensory issues, as tannins have been associated with astringency and bitter taste, and thus effective phlorotannins doses may negatively affect the sensory attributes of foods. These drawbacks expose the need of applying smart strategies to develop a final product providing the necessary protective mechanisms to maintain the active molecular form of phlorotannins up to the consumption time, also controlling their release upon arrival to the gut. In this context, the impact of these technological processes (from pre-processing to the passage through the GIT) on phlorotannins stability, as well as the innovative developed approaches to overcome these issues will be deeply discussed in this review. Besides, recent findings related to the phlorotannins' health benefits will be pointed out. Special attention on the potential incorporation of phlorotannins into functional foods will be also put it on.

Algae Polyphenolic Compounds and Modern Antibacterial Strategies: Current Achievements and Immediate Prospects

The increasing drug resistance of pathogenic microorganisms raises concern worldwide and necessitates the search for new natural compounds with antibacterial properties. Marine algae are considered a natural and attractive biotechnological source of novel antibiotics. The high antimicrobial activity of their polyphenolic compounds is a promising basis for designing innovative pharmaceuticals. They can become both a serious alternative to traditional antimicrobial agents and an effective supplement to antibiotic therapy. The present review summarizes the results of numerous studies on polyphenols from algae and the range of biological activities that determine their biomedical significance. The main focus is put on a group of the polyphenolic metabolites referred to as phlorotannins and, particularly, on their structural diversity and mechanisms of antimicrobial effects. Brown algae are an almost inexhaustible resource with a high biotechnological potential for obtaining these polyfunctional compounds. An opinion is expressed that the effectiveness of the antibacterial activity of phlorotannins depends on the methods of their extraction aimed at preserving the phenolic structure. The use of modern analytical tools opens up a broad range of opportunities for studying the metabolic pathways of phlorotannins and identifying their structural and functional relationships. The high antimicrobial activity of phlorotannins against both Gram-positive and Gram-negative bacteria provides a promising framework for creating novel drugs to be used in the treatment and prevention of infectious diseases.

Living with Breakthrough: Two-Dimensional Liquid-Chromatography Separations of a Water-Soluble Synthetically Grafted Bio-Polymer

In this study, we evaluate the use of various two-dimensional liquid chromatographic methods to characterize water-soluble, synthetically grafted bio-polymers, consisting of long poly(acrylic acid) chains and short maltodextrin grafts. The confirmation of the presence of grafting and the estimation of its extent is challenging. It is complicated by the limited solubility of polymers, their structural dispersity and chemical heterogeneity. Moreover, the starting materials (and other reagents, reaction products and additives) may be present in the product. Reversed-phase liquid chromatography (RPLC), hydrophilic-interaction liquid chromatography (HILIC) and size-exclusion chromatography (SEC) were used to characterize the product, as well as the starting materials. Additionally, fractions were collected for off-line characterization by infrared spectroscopy and mass spectrometry. The one-dimensional separation methods were found to be inconclusive regarding the grafting question. Breakthrough (the early elution of polymer fractions due to strong injection solvents) is shown to be a perpetual problem. This issue is not solved by comprehensive two-dimensional liquid chromatography (LC × LC), but information demonstrating the success of the grafting reaction could be obtained. SEC × RPLC and HILIC × RPLC separations are presented and discussed.

Determination of the Metabolite Content of Brassica juncea Cultivars Using Comprehensive Two-Dimensional Liquid Chromatography Coupled with a Photodiode Array and Mass Spectrometry Detection

Plant-based foods are characterized by significant amounts of bioactive molecules with desirable health benefits beyond basic nutrition. The Brassicaceae (Cruciferae) family consists of 350 genera; among them, Brassica is the most important one, which includes some crops and species of great worldwide economic importance. In this work, the metabolite content of three different cultivars of Brassica juncea, namely ISCI Top, “Broad-leaf,” and ISCI 99, was determined using comprehensive two-dimensional liquid chromatography coupled with a photodiode array and mass spectrometry detection. The analyses were carried out under reversed-phase conditions in both dimensions, using a combination of a 250-mm microbore cyano column and a 50-mm RP-Amide column in the first and second dimension (²D), respectively. A multi (three-step) segmented-in-fraction gradient for the ²D separation was advantageously investigated here for the first time, leading to the identification of 37 metabolites. In terms of resolving power, orthogonality values ranged from 62% to 69%, whereas the corrected peak capacity values were the highest for B. juncea ISCI Top (639), followed by B. juncea “Broad-leaf” (502). Regarding quantification, B. juncea cv. “Broad-leaf” presented the highest flavonoid content (1962.61 mg/kg) followed by B. juncea cv. ISCI Top (1002.03 mg/kg) and B. juncea cv. ISCI 99 (211.37 mg/kg).

The Quest for Phenolic Compounds from Macroalgae: A Review of Extraction and Identification Methodologies

The current interest of the scientific community for the exploitation of high-value compounds from macroalgae is related to the increasing knowledge of their biological activities and health benefits. Macroalgae phenolic compounds, particularly phlorotannins, have gained particular attention due to their specific bioactivities, including antioxidant, antiproliferative, or antidiabetic. Notwithstanding, the characterization of macroalgae phenolic compounds is a multi-step task, with high challenges associated with their isolation and characterization, due to the highly complex and polysaccharide-rich matrix of macroalgae. Therefore, this fraction is far from being fully explored. In fact, a critical revision of the extraction and characterization methodologies already used in the analysis of phenolic compounds from macroalgae is lacking in the literature, and it is of uttermost importance to compile validated methodologies and discourage misleading practices. The aim of this review is to discuss the state-of-the-art of phenolic compounds already identified in green, red, and brown macroalgae, reviewing their structural classification, as well as critically discussing extraction methodologies, chromatographic separation techniques, and the analytical strategies for their characterization, including information about structural identification techniques and key spectroscopic profiles. For the first time, mass spectrometry data of phlorotannins, a chemical family quite exclusive of macroalgae, is compiled and discussed.

Polyphenol-Rich Extracts from Brown Macroalgae Lessonia trabeculate Attenuate Hyperglycemia and Modulate Gut Microbiota in High-Fat Diet and Streptozotocin-Induced Diabetic Rats

Brown macroalgae are an important source of polyphenols with multiple health functions. In this work, polyphenol extracts from Lessonia trabeculate were purified and investigated for the antidiabetic activity in vitro and in vivo. The purified polyphenol extracts exhibited good antioxidant activities, α-glucosidase and lipase inhibition activities (IC50 < 0.25 mg/mL). The HPLC-DAD-ESI-MS/MS analysis indicated that the compounds in polyphenol extracts were mainly phlorotannin derivatives, phenolic acid derivatives, and gallocatechin derivatives. In vivo, C57BL/6J rats treated with polyphenol extracts for 4 weeks had lower fasting blood glucose levels, insulin levels, as well as better serum lipid profiles and antioxidant stress parameters, compared with the diabetic control (DC) group. Histopathology revealed that polyphenol extracts preserved the architecture and function of the liver. Short-chain fatty acid contents in rats' fecal samples with polyphenols administration were significantly recovered as compared with the DC group. Furthermore, the gut microflora of rats was investigated with high-throughput 16S rRNA gene sequencing and results indicated that polyphenol extracts had a positive effect on regulating the dysbiosis of the microbial ecology in diabetic rats. All of the results from the study provided a scientific reference of the potentially beneficial effects of L. trabeculate polyphenols on diabetes management.

A critical review of analytical methods used for the chemical characterisation and quantification of phlorotannin compounds in brown seaweeds

INTRODUCTION

Phlorotannins, the phenolic compounds found in brown seaweeds, are a unique and diverse class of compounds showing a huge potential for food and pharmaceutical applications.

OBJECTIVE

This review will give an account of the colorimetric assays used and a discussion of their quantitative and qualitative analytical shortcomings. It will also discuss other more complex and modern analytical chemistry methods that are currently being developed to study phlorotannins. The purpose of this review is to increase awareness of these bioactive compounds and promote further development of robust analytical methods for use in biology, food science, pharmacology and biomedical and cosmeceutical sciences.

RESULTS

Whilst the biological activity and huge commercial potential of the phlorotannins has been widely reported throughout the literature, the chemical structures and reactivity of these compounds is still not well understood. The phlorotannin content of seaweed is usually characterised using colorimetric assays. However, although these methods give a reasonable overall estimation of the total phenolic content, they lack precision and specificity.

CONCLUSION

This review highlights the strengths and weaknesses of commonly used colorimetric assays. Novel techniques are highlighted using more selective chemistry to identify this class of compounds.

Phlorotannins from Undaria pinnatifida Sporophyll: Extraction, Antioxidant, and Anti-Inflammatory Activities

Undaria pinnatifida sporophyll (U. pinnatifida) is a major byproduct of U. pinnatifida (a brown algae) processing. Its phenolic constituents, phlorotannins, are of special interest due to their intrinsic ability to precipitate proteins. Herein, a high-temperature extraction procedure was used to isolate these biologically active compounds. The heating temperature, heating time, and extraction solvent (ethanol) concentration were examined with response surface analysis to determine the optimal conditions to achieve the maximum extraction rate. The analysis revealed the optimal conditions to be: 170 °C of heating temperature, 5.2 h of heating time, and 52% ethanol concentration for a yield of 10.7 ± 0.2 mg gallic acid equivalent/g dry weight (GAE/g DW) of sample. Compared to epigallocatechin gallate (EGCG), the extracted phlorotannins displayed higher antioxidant activity on H2O2-induced RAW 264.7 cells with improved efficiency. Furthermore, the compounds exhibited strong anti-inflammatory activity. These findings potentially can be utilized to guide development of novel functional foods and food supplements from sea-originated resources such as brown algae.