Pulsed electric field assisted extraction of nutritionally valuable compounds from microalgae Nannochloropsis spp. using the binary mixture of organic solvents and water

Combining high pressure and electric fields towards Nannochloropsis oculata eicosapentaenoic acid-rich extracts

Nannochloropsis oculata is naturally rich in eicosapentaenoic acid (EPA). To turn this microalga into an economically viable source for commercial applications, extraction efficiency must be achieved. Pursuing this goal, emerging technologies such as high hydrostatic pressure (HHP) and moderate electric fields (MEF) were tested, aiming to increase EPA accessibility and subsequent extraction yields. The innovative approach used in this study combined these technologies and associated tailored, less hazardous different solvent mixtures (SM) with distinct polarity indexes. Although the classical Folch SM with chloroform: methanol (PI 4.4) provided the highest yield concerning total lipids (166.4 mg_lipid/g_biomass), diethyl ether: ethanol (PI 3.6) presented statistically higher values in terms of EPA per biomass, corresponding to 1.3-fold increase. When SM were used in HHP and MEF, neither technology independently improved EPA extraction yields, although the sequential combination of technologies did result in 62% increment in EPA extraction. Overall, the SM and extraction methodologies tested (HHP-200 MPa, 21 °C, 15 min, followed by MEF processing at 40 °C, 15 min) enabled increased EPA extraction yields from wet N. oculata biomass. These findings are of high relevance for the food and pharmaceutical industries, providing viable alternatives to the "classical" extraction methodologies and solvents, with increased yields and lower environmental impact. KEY POINTS: • Et₂O: EtOH is a less toxic and more efficient alternative to Folch solvent mixture • HHP or MEF per se was not able to significantly increase EPA extraction yield • Combinations of HHP and MEF technologies increased both lipids and EPA yields.

Extraction of Valuable Biomolecules from the Microalga Haematococcus pluvialis Assisted by Electrotechnologies

The freshwater microalga Haematococcus pluvialis is well known as the cell factory for natural astaxanthin, which composes up to 4-7% of its total dry weight. The bioaccumulation of astaxanthin in H. pluvialis cysts seems to be a very complex process that depends on different stress conditions during its cultivation. The red cysts of H. pluvialis develop thick and rigid cell walls under stress growing conditions. Thus, the biomolecule extraction requires general cell disruption technologies to reach a high recovery rate. This short review provides an analysis of the different steps in H. pluvialis's up and downstream processing including cultivation and harvesting of biomass, cell disruption, extraction and purification techniques. Useful information on the structure of H. pluvialis's cells, biomolecular composition and properties and the bioactivity of astaxanthin is collected. Special emphasis is given to the recent progress in application of different electrotechnologies during the growth stages and for assistance of the recovery of different biomolecules from H. pluvialis.

Pulsed Electric Fields (PEF) and Accelerated Solvent Extraction (ASE) for Valorization of Red (Aristeus antennatus) and Camarote (Melicertus kerathurus) Shrimp Side Streams: Antioxidant and HPLC Evaluation of the Carotenoid Astaxanthin Recovery

Shrimp side streams represent an important natural source of astaxanthin. Optimization of the astaxanthin extraction process from shrimp side streams is of great importance for the valorization of crustacean side streams and the development of astaxanthin-related products. The combined and independent effects of two innovative extraction technologies (pulsed electric fields (PEFs) and accelerated solvent extraction (ASE)) alone and/or combined in a sequential step, using two different solvents on astaxanthin extraction from two shrimp species, were evaluated. Astaxanthin content in the extracts of shrimp side streams was determined by both spectrophotometric and HPLC assays, being the determination of the carotenoid profiles performed by HPLC analysis. Compared to a solvent extraction control procedure, the astaxanthin content was increased after ASE and PEF treatments, for both shrimp species, independently of the solvent used. The highest recovery (585.90 µg/g) was obtained for the species A. antennatus, with the solvent DMSO when PEF and ASE were combined, while the increase in antioxidant capacity varied depending on the solvent used. HPLC analysis of the samples revealed the presence of unesterified (all-E) astaxanthin, four unesterified Z isomers of astaxanthin and many unresolved astaxanthin esters. Both technologies are useful tools to recover antioxidant valuable carotenoids such as astaxanthin from shrimp side streams.

Microalgae-Derived Pigments for the Food Industry

In the food industry, manufacturers and customers have paid more attention to natural pigments instead of the synthetic counterparts for their excellent coloring ability and healthy properties. Microalgae are proven as one of the major photosynthesizers of naturally derived commercial pigments, gaining higher value in the global food pigment market. Microalgae-derived pigments, especially chlorophylls, carotenoids and phycobiliproteins, have unique colors and molecular structures, respectively, and show different physiological activities and health effects in the human body. This review provides recent updates on characteristics, application fields, stability in production and extraction processes of chlorophylls, carotenoids and phycobiliproteins to standardize and analyze their commercial production from microalgae. Potential food commodities for the pigment as eco-friendly colorants, nutraceuticals, and antioxidants are summarized for the target products. Then, recent cultivation strategies, metabolic and genomic designs are presented for high pigment productivity. Technical bottlenecks of downstream processing are discussed for improved stability and bioaccessibility during production. The production strategies of microalgal pigments have been exploited to varying degrees, with some already being applied at scale while others remain at the laboratory level. Finally, some factors affecting their global market value and future prospects are proposed. The microalgae-derived pigments have great potential in the food industry due to their high nutritional value and competitive production cost.

Can Growth of Nannochloropsis oculata under Modulated Stress Enhance Its Lipid-Associated Biological Properties?

Nannochloropsis oculata is well-recognized as a potential microalgal source of valuable compounds such as polyunsaturated fatty acids, particularly, eicosapentaenoic acid (EPA). The content and profile of these lipids is highly dependent on the growth conditions and can, therefore, be tailored through modulation of the growth parameters, specifically, temperature. Moreover, biological activities are composition dependent. In the present work, lipid extracts obtained from N. oculata, grown under constant temperature and under modulated temperature stress (to increase EPA content; Str) were characterized by GC-FID and several bioactivities were evaluated, namely, antioxidant (L-ORAC_FL), cytotoxic (MTT), adipolytic, anti-hepatic lipid accumulation (steatosis), and anti-inflammatory properties. Both extracts exhibited antioxidant activity (c.a. 49 µmol Trolox_equivalent/mg_extract) and the absence of toxicity (up to 800 µg/mL) toward colon and hepatic cells, adipocytes, and macrophages. They also induced adipolysis and the inhibition of triglycerides hepatic accumulation, with a higher impact from Str. In addition, anti-inflammatory activity was observed in the lipopolysaccharide-induced inflammation of macrophages in the presence of either extract, since lower levels of pro-inflammatory interleukin-6 and interferon-β were obtained, specifically by Str. The results presented herein revealed that modulated temperature stress may enhance the health effects of N. oculata lipid extracts, which may be safely utilized to formulate novel food products.

A Review of Development and Utilization for Edible Fungal Polysaccharides: Extraction, Chemical Characteristics, and Bioactivities

Edible fungi, commonly known as mushrooms, are precious medicinal and edible homologous gifts from nature to us. Because of their distinctive flavor and exceptional nutritional and medicinal value, they have been a frequent visitor to people’s dining tables and have become a hot star in the healthcare, pharmaceutical, and cosmetics industries. Edible fungal polysaccharides (EFPs) are an essential nutrient for edible fungi to exert bioactivity. They have attracted much attention because of their antioxidant, immunomodulatory, antitumor, hypoglycemic, and hypolipidemic bioactivities. As a result, EFPs have demonstrated outstanding potential over the past few decades in various disciplines, including molecular biology, immunology, biotechnology, and pharmaceutical chemistry. However, the complexity of EFPs and the significant impact of mushroom variety and extraction techniques on their bioactivities prevents a complete investigation of their biological features. Therefore, the authors of this paper thoroughly reviewed the comparison of different extraction methods of EFPs and their advantages and disadvantages. In addition, the molecular weight, monosaccharide composition, and glycosidic bond type and backbone structure of EFPs are described in detail. Moreover, the in vitro and in vivo bioactivities of EFPs extracted by different methods and their potential regulatory mechanisms are summarized. These provide a valuable reference for improving the extraction process of EFPs and their production and development in the pharmaceutical field.

Pulsed electric field assisted extraction of natural food pigments and colorings from plant matrices

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Pulsed electric field (PEF) technology enables the extraction of food pigments at lower temperatures.

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PEF process intensification may reduce the extraction yield depending on the plant matrix.

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Coupling PEF with other emerging technologies is a smart strategy to extract natural pigments.

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The application of PEF technology in natural food pigment extraction still requires further studies.

Coloring compounds are widely applied to manufacturing foods and beverages. The worldwide food market is replacing artificial colorants with natural alternatives, given the increased consumer demand for natural products. However, these substitutes are still an issue due to their high production cost and low chemical and physical stability. Furthermore, natural pigments are highly sensitive to processes applied in conventional extraction techniques, such as thermal, mechanical, and chemical stresses. In this regard, pulsed electric field (PEF) technology has emerged as a promising non-thermal alternative for recovering and producing natural colorings from food matrices. Its action mechanism on cell structures through the electroporation effect is a smart alternative to overcoming the challenging issues associated with producing natural colorants. In this scenario, this review provides an overview of the PEF assisted extraction of natural pigments and colorants, such as anthocyanins (red-blue-purple), betalains (red), carotenoids (yellow-orange-red), and chlorophylls (green) from plant sources. Moreover, the potential and limitations of this emerging technology to integrate the extraction process of natural colorants were discussed.

Influence of Geographical Location of Spirulina (Arthrospira platensis) on the Recovery of Bioactive Compounds Assisted by Pulsed Electric Fields

Spirulina (Arthrospira platensis) has been consumed by humans since ancient times. It is rich in high added-value compounds such as chlorophylls, carotenoids and polyphenols. Pulsed electric fields (PEF) is an innovative non-thermal technique that improves the extraction of bioactive compounds from diverse sources. PEF pre-treatment (3 kV/cm, 100 kJ/kg) combined with supplementary extraction with binary solvents at different times was evaluated to obtain the optimal conditions for extraction. In addition, the results obtained were compared with conventional treatment (without PEF pre-treatment and constant shaking) and different strains of Spirulina from diverse geographical locations. The optimal extraction conditions for recovering the bioactive compounds were obtained after applying PEF treatment combined with the binary mixture EtOH/H2O for 180 min. The recovery of total phenolic content (TPC) (19.76 ± 0.50 mg/g DM (dry matter) and carotenoids (0.50 ± 0.01 mg/g DM) was more efficient in the Spirulina from Spain. On the other hand, there was a higher recovery of chlorophylls in the Spirulina from China. The highest extraction of total antioxidant compounds was in Spirulina from Costa Rica. These results show that PEF, solvents and the condition of growing affect the extraction of antioxidant bioactive compounds from Spirulina. The combination of PEF and EtOH/H2O is a promising technology due to its environmental sustainability.

Applications of green technologies-based approaches for food safety enhancement: A comprehensive review

Food is the basic necessity for life that always motivated man for its preservation and making it available for an extended period. Food scientists always tried to preserve it with minimum deterioration in quality by employing and investigating innovative preservation techniques. The food sector always remained in search of eco-friendly and sustainable solutions to tackle food safety challenges. Green technologies (ozone, pulsed electric field, ohmic heating, photosensitization, ultraviolet radiations, high-pressure processing, ultrasonic, nanotechnology) are in high demand owing to their eco-friendly, rapid, efficient, and effective nature in controlling microbes with a negligible residual impact on food quality during processing. The use of green technologies would be a desirable substitute for conventionally available preservation techniques. This paper discusses different food preservation techniques with special reference to green technologies to minimize the deleterious impact on the environment and employs these innovative technologies to play role in enhancing the food safety.

Can Pulsed Electric Fields Treated Algal Cells Be Used as Stationary Phase in Chromatography?

Microalgae are utilized for various purposes through cell content extraction and application. Cell walls are not utilized and not studied in an extensive manner. At the same time, composition of multilayer and fibrillar structures with various chemical compositions depends on microalgae species, they present an interesting object for chromatography. However, it requires the application of novel processing technologies (such as pulsed electric fields [PEFs]), which are able to selectively permeabilize the cell walls with pores of various sizes and shapes. The current review indicates the application of potential of microalgae cell walls for separation by size exclusion, ion-exchange, and hydrophobic interaction chromatography. However, such a hypothesis should be further experimentally proven.

Recovering Microalgal Bioresources: A Review of Cell Disruption Methods and Extraction Technologies

Microalgae have evolved into a promising sustainable source of a wide range of compounds, including protein, carbohydrates, biomass, vitamins, animal feed, and cosmetic products. The process of extraction of intracellular composites in the microalgae industry is largely determined by the microalgal species, cultivation methods, cell wall disruption techniques, and extraction strategies. Various techniques have been applied to disrupt the cell wall and recover the intracellular molecules from microalgae, including non-mechanical, mechanical, and combined methods. A comprehensive understanding of the cell disruption processes in each method is essential to improve the efficiency of current technologies and further development of new methods in this field. In this review, an overview of microalgal cell disruption techniques and an analysis of their performance and challenges are provided. A number of studies on cell disruption and microalgae extraction are examined in order to highlight the key challenges facing the field of microalgae and their future prospects. In addition, the amount of product recovery for each species of microalgae and the important parameters for each technique are discussed. Finally, pulsed electric field (PEF)-assisted treatments, which are becoming an attractive option due to their simplicity and effectiveness in extracting microalgae compounds, are discussed in detail.

Application of Pulsed Electric Fields and High-Pressure Homogenization in Biorefinery Cascade of C. vulgaris Microalgae

In this study, a cascaded cell disintegration process, based on pulsed electric fields (PEF - 20 kV/cm, 100 kJ/kg_SUSP.) and high-pressure homogenization (HPH - 150 MPa, 5 passes) was designed for the efficient and selective release of intracellular compounds (water-soluble proteins, carbohydrates, and lipids) from C. vulgaris suspensions during extraction in water (25 °C, 1 h) and ethyl acetate (25 °C, 3 h). Recovery yields of target compounds from cascaded treatments (PEF + HPH) were compared with those observed when applying PEF and HPH treatments individually. Particle size distribution and scanning electron microscopy analyses showed that PEF treatment alone did not induce any measurable effect on cell shape/structure, whereas HPH caused complete cell fragmentation and debris formation, with an undifferentiated release of intracellular matter. Spectra measurements demonstrated that, in comparison with HPH alone, cascaded treatments increased the selectivity of extraction and improved the yields of carbohydrates and lipids, while higher yields of water-soluble proteins were measured for HPH alone. This work, therefore, demonstrates the feasibility of sequentially applying PEF and HPH treatments in the biorefinery of microalgae, projecting a beneficial impact in terms of process economics due to the potential reduction of the energy requirements for separation/purification stages.

Exploring the Potential of Icelandic Seaweeds Extracts Produced by Aqueous Pulsed Electric Fields-Assisted Extraction for Cosmetic Applications

A growing concern for overall health is driving a global market of natural ingredients not only in the food industry but also in the cosmetic field. In this study, a screening on potential cosmetic applications of aqueous extracts from three Icelandic seaweeds produced by pulsed electric fields (PEF) was performed. Produced extracts by PEF from Ulva lactuca, Alaria esculenta and Palmaria palmata were compared with the traditional hot water extraction in terms of polyphenol, flavonoid and carbohydrate content. Moreover, antioxidant properties and enzymatic inhibitory activities were evaluated by using in vitro assays. PEF exhibited similar results to the traditional method, showing several advantages such as its non-thermal nature and shorter extraction time. Amongst the three Icelandic species, Alaria esculenta showed the highest content of phenolic (mean value 8869.7 µg GAE/g dw) and flavonoid (mean value 12,098.7 µg QE/g dw) compounds, also exhibiting the highest antioxidant capacities. Moreover, Alaria esculenta extracts exhibited excellent anti-enzymatic activities (76.9, 72.8, 93.0 and 100% for collagenase, elastase, tyrosinase and hyaluronidase, respectively) for their use in skin whitening and anti-aging products. Thus, our preliminary study suggests that Icelandic Alaria esculenta-based extracts produced by PEF could be used as potential ingredients for natural cosmetic and cosmeceutical formulations.

Role of Extracts Obtained from Rainbow Trout and Sole Side Streams by Accelerated Solvent Extraction and Pulsed Electric Fields on Modulating Bacterial and Anti-Inflammatory Activities

In this study, accelerated solvent extraction (ASE) and pulsed electric field (PEF) were used as innovative approaches to recover extracts from rainbow trout and sole side streams rich in high-added-value compounds. Then, after aseptic filtration, the impact of the obtained extracts on bacterial growth and anti-inflammatory potential was evaluated. Moreover, the protein content and the total antioxidant capacity of the samples were determined. The results showed that some extracts could inhibit the growth of pathogenic bacteria, including the ASE rainbow trout skin and the PEF sole viscera extracts, which showed significant antibacterial activity on Staphylococcus aureus. The PEF sole viscera extract also showed an inhibitory effect on the growth of Salmonella. In addition, some extracts promoted probiotic bacteria growth. For example, the PEF rainbow trout head and skin extracts promoted Lactobacillus casei growth, while the ASE rainbow trout head and skin extracts promoted Bifidobacterium lactis growth. In addition, some samples, such as the ASE rainbow trout viscera and the PEF sole skin extracts had interesting anti-inflammatory properties. Therefore, the use of ASE and PEF can be considered as useful strategies to recover antimicrobial, prebiotic and anti-inflammatory extracts from rainbow trout and sole side streams, although it is necessary to evaluate each specific side stream.

Emerging Green Techniques for the Extraction of Antioxidants from Agri-Food By-Products as Promising Ingredients for the Food Industry

Nowadays, the food industry is heavily involved in searching for green sources of valuable compounds, to be employed as potential food ingredients, to cater to the evolving consumers’ requirements for health-beneficial food ingredients. In this frame, agri-food by-products represent a low-cost source of natural bioactive compounds, including antioxidants. However, to effectively recover these intracellular compounds, it is necessary to reduce the mass transfer resistances represented by the cellular envelope, within which they are localized, to enhance their extractability. To this purpose, emerging extraction technologies, have been proposed, including Supercritical Fluid Extraction, Microwave-Assisted Extraction, Ultrasound-Assisted Extraction, High-Pressure Homogenization, Pulsed Electric Fields, High Voltage Electrical Discharges. These technologies demonstrated to be a sustainable alternative to conventional extraction, showing the potential to increase the extraction yield, decrease the extraction time and solvent consumption. Additionally, in green extraction processes, also the contribution of solvent selection, as well as environmental and economic aspects, represent a key factor. Therefore, this review focused on critically analyzing the main findings on the synergistic effect of low environmental impact technologies and green solvents towards the green extraction of antioxidants from food by-products, by discussing the main associated advantages and drawbacks, and the criteria of selection for process sustainability.

Extraction of Antioxidant Compounds and Pigments from Spirulina (Arthrospira platensis) Assisted by Pulsed Electric Fields and the Binary Mixture of Organic Solvents and Water

The application of pulsed electric fields (PEF) is an innovative extraction technology promoting cell membrane electroporation, thus allowing for an efficient recovery, from an energy point of view, of antioxidant compounds (chlorophylls, carotenoids, total phenolic compounds, etc.) from microalgae. Due to its selectivity and high extraction yield, the effects of PEF pre-treatment (3 kV/cm, 100 kJ/kg) combined with supplementary extraction at different times (5–180 min) and with different solvents (ethanol (EtOH)/H2O, 50:50, v/v; dimethyl sulfoxide (DMSO)/H2O, 50:50, v/v) were evaluated in order to obtain the optimal conditions for the extraction of different antioxidant compounds and pigments. In addition, the results obtained were compared with those of a conventional treatment (without PEF pre-treatment but with constant shaking). After carrying out the different experiments, the best extraction conditions to recover the different compounds were obtained after applying PEF pre-treatment combined with the binary mixture EtOH/H2O, 50:50, v/v, for 60–120 min. PEF extraction was more efficient throughout the study, especially at short extraction times (5–15 min). In this sense, recovery of 55–60%, 85–90%, and 60–70% was obtained for chlorophylls, carotenoids, and total phenolic compounds, respectively, compared to the maximum total extracted amount. These results show that PEF improves the extraction yield of antioxidant bioactive compounds from microalgae and is a promising technology due to its profitability and environmental sustainability.

Extraction of Pigments from Microalgae and Cyanobacteria—A Review on Current Methodologies

Pigments from microalgae and cyanobacteria have attracted great interest for industrial applications due to their bioactive potential and their natural product attributes. These pigments are usually sold as extracts, to overcome purification costs. The extraction of these compounds is based on cell disruption methodologies and chemical solubility of compounds. Different cell disruption methodologies have been used for pigment extraction, such as sonication, homogenization, high-pressure, CO2 supercritical fluid extraction, enzymatic extraction, and some other promising extraction methodologies such as ohmic heating and electric pulse technologies. The biggest constrain on pigment bioprocessing comes from the installation and operation costs; thus, fundamental and applied research are still needed to overcome such constrains and give the microalgae and cyanobacteria industry an opportunity in the world market. In this review, the main extraction methodologies will be discussed, taking into account the advantages and disadvantages for each kind of pigment, type of organism, cost, and final market.

Ultrasound Extraction Mediated Recovery of Nutrients and Antioxidant Bioactive Compounds from Phaeodactylum tricornutum Microalgae

In recent years, a growing interest has been shown in the use of microalgae due to their interesting nutritional and bioactive profiles. Green innovative processing technologies such as ultrasound-assisted extraction (UAE) avoid the use of toxic solvents and high temperatures, being a sustainable alternative in comparison with traditional extraction methods. The present study aims to evaluate the recovery of high added-value compounds from Phaedoactylum tricornutum assisted by ultrasound. To optimize the UAE of proteins, carbohydrates, pigments and antioxidant compounds, a response surface methodology was used. Carbohydrate extraction was positively affected by the temperature. However, for the extraction of carotenoids, the most influential factor was the extraction time. The total polyphenols were only significantly affected by the extraction time. Finally, the antioxidant capacity, measured by 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS), was strongly modulated by the extraction time, while for the oxygen radical antioxidant capacity (ORAC) assay, the most important parameter was the temperature, followed by the extraction time. The optimal conditions for the maximum extraction of nutrients, bioactive compounds and antioxidant capacity were 30 min, 50 ºC and a pH of 8.5. Finally, it has been seen that with these conditions, the extraction of fucoxanthin is allowed, although no differences were found between an ultrasound-assisted extraction and a shaking extraction (control).

Extraction, Properties, and Applications of Bioactive Compounds Obtained from Microalgae

With the increase in the global population, getting new sources of food is essential. One of the solutions can be found in the oceans due to algae. Microalgae are aquatic photosynthetic organisms used mainly due to their variety of bioactive compounds. The consumption of microalgae has been carried out for centuries and is recommended by organizations, such as OMS and FAO, due to its nutritional value and its properties. Based on the existing literature, there is substantial evidence of the nutritional quality of the algae as well as their functional elements. However, much quantification is still necessary, as well as studying possible adverse effects. The present review describes the compounds of alimentary interest present in these algae as well as different extraction techniques assisted by different energetic mechanisms (such as heat, supercritical-fluid, microwave, ultrasound, enzymes, electric field, high hydrostatic pressure, among others). The most challenging and crucial issues are reducing microalgae growth cost and optimizing extraction techniques. This review aimed a better understanding of the uses of microalgae for new researches in nutrition. Since the use of microalgae is still a field in which there is much to discover, it is likely that more benefits will be found in its consumption.

Pulsed Electric Fields-Assisted Extraction of Valuable Compounds From Arthrospira Platensis: Effect of Pulse Polarity and Mild Heating

The present study aimed to investigate the effect of the main pulsed electric field (PEF) process parameters on the cell damages of A. platensis microalgae and the extractability of valuable compounds [water-soluble proteins (WSP), C-phycocyanin (C-PC), and carbohydrates (CH)]. Aqueous microalgae suspensions (2%, w/w) were PEF-treated at variable field strength (E = 10, 20, 30 kV/cm), total specific energy (W T = 20, 60, 100 kJ/kgsusp), and inlet temperature (25, 35, 45°C), with either monopolar or bipolar square wave pulses (5 μs of width, delay time between pulses of opposite polarities = 1, 5, 10, 20 μs), prior to extraction with water at room temperature (25°C) for up to 3 h. High-pressure homogenization (HPH) treatment (P = 150 MPa, 3 passes) was used to achieve complete cell disruption to quantify the total extractable content of target intracellular compounds. Scanning electron microscopy (SEM) and optical microscopy analyses clearly showed that PEF merely electroporated the membranes of algae cell, without damaging the cell structure and forming cell debris. The application of PEF treatment (monopolar pulses, 20 kV/cm and 100 kJ/kgsusp) at room temperature significantly enhanced the extraction yield of WSP [17.4% dry weight (DW)], CH (10.1% DW), and C-PC (2.1% DW), in comparison with the untreated samples. Bipolar pulses appeared less effective than monopolar pulses and led to extraction yields dependent on the delay time. Additionally, regardless of pulse polarity, a clear synergistic effect of the combined PEF (20 kV/cm and 100 kJ/kgsusp)-temperature (35°C) treatment was detected, which enabled the extraction of up to 37.4% (w/w) of total WSP, 73.8% of total CH, and 73.7% of total C-PC. Remarkably, the PEF treatment enabled to obtain C-phycocyanin extract with higher purity than that obtained using HPH treatment. The results obtained in this work suggest that the application of PEF combined with mild heating could represent a suitable approach for the efficient recovery of water-soluble compounds microalgal biomass.

Improved Extraction Efficiency of Antioxidant Bioactive Compounds from Tetraselmis chuii and Phaedoactylum tricornutum Using Pulsed Electric Fields

Pulsed electric fields (PEF) is a promising technology that allows the selective extraction of high-added value compounds by electroporation. Thus, PEF provides numerous opportunities for the energy efficient isolation of valuable microalgal bioactive substances (i.e., pigments and polyphenols). The efficiency of PEF-assisted extraction combined with aqueous or dimethyl sulfoxide (DMSO) solvents in recovering pigments and polyphenols from microalgae Tetraselmis chuii (T. chuii) and Phaeodactylum tricornutum (P. tricornutum) was evaluated. Two PEF treatments were applied: (1 kV/cm/400 pulses, 3 kV/cm/45 pulses), with a specific energy input of 100 kJ/kg. The total antioxidant capacity (TAC) was positively influenced by the use of DMSO. The highest TAC in the T. chuii culture was achieved at a lower extraction time and electric field than for P. tricornutum. The use of DMSO only improved the polyphenols' extraction for P. tricornutum, whereas the PEF and extraction time were more important for T. chuii. Carotenoids and chlorophyll a were more efficiently extracted using DMSO, while chlorophyll b levels were higher following aqueous extraction for both microalgae. In P. tricornutum, the TAC and pigment extraction efficiency were in general higher at lower extraction times. It can be concluded that PEF may be a promising alternative for the enhancement of the selective extraction of antioxidant bioactive compounds from microalgae.

Effect of Pulsed Electric Fields on the Growth and Acidification Kinetics of Lactobacillus delbrueckii Subsp. bulgaricus

The aim of this work was to investigate the effect of pulsed electric fields (PEF) on the growth and acidification kinetics of Lactobacillus delbrueckii subsp. bulgaricus CFL1 during fermentation. The PEF treatments were applied during the fermentation process using a recirculation pump and a PEF treatment chamber coupled with a PEF generator. The medium flow rate through the chamber was first optimized to obtain the same growth and acidification kinetics than the control fermentation without medium recirculation. Different PEF intensities (60-428 V cm-1) were then applied to the culture medium to study the impact of PEF on the cells' behavior. The growth and acidification kinetics were recorded during the fermentation and the specific growth rates µ, pH, and acidification rate (dpH/dt) were assessed. The results obtained showed a biphasic growth by applying high PEF intensities (beyond 285 V cm-1) with the presence of two maximal specific growth rates and a decrease in the acidification activities. It was demonstrated that the cells were stressed during the PEF treatment, but presented an accelerated growth after stopping it, leading thereby to similar absorbance and pH at the end of the fermentation. These results show the great potential of PEF technology to be applied to generate low acidified products by performing PEF-assisted fermentations.

Matrix solid-phase dispersion as a greener alternative to obtain bioactive extracts from Haematococcus pluvialis. Characterization by UHPLC-QToF

So far, research on the microalga Haematococcus pluvialis has been focused mainly on the exploitation of its high astaxanthin content, leaving aside the use of other bioactive compounds present. This study is focused on obtaining and characterizing extracts enriched in bioactive compounds from this microalga red aplanospores. This is performed by means of Matrix Solid-Phase Dispersion (MSPD) extraction process, in an environmentally friendly way with low energy consumption and GRAS solvents. The effects of extraction parameters, particularly the extraction solvents (ethanol, ethyl lactate and water) are studied, in order to obtain maximum recovery of the main antioxidant compounds of interest (carotenoids, fatty acids and derivatives). Characterization of extracts is carried out by HPLC-DAD (High Performance Liquid Chromatography Diode Array Detector) and UHPLC-QToF (Ultra High-Performance Liquid Chromatography Quadrupole Time-of-Flight). The results show that MSPD produced extracts with higher bioactive compound recoveries than conventional cell disruption extractions. At the same time, a novel untargeted characterization for this species is performed, identifying compounds not previously dated in H. pluvialis, which include 10-phenyldecanoic acid and the -oxo and -hydroxy derivatives of palmitic acid. This approach, first applied to a freshwater microalgae, characterized by rigid and resistant aplanospores, provided a synergistic and sustainable extract, giving a broader focus on the use of this microalga.

Untargeted characterization and alternative extraction of carotenoids, fatty acids, and new bioactive compounds from microalga Haematococcus pluvialis using GRAS solvents.

Fungi as a Potential Source of Pigments: Harnessing Filamentous Fungi

The growing concern over the harmful effects of synthetic colorants on both the consumer and the environment has raised a strong interest in natural coloring alternatives. As a result the worldwide demand for colorants of natural origin is rapidly increasing in the food, cosmetic and textile sectors. Natural colorants have the capacity to be used for a variety of industrial applications, for instance, as dyes for textile and non-textile substrates such as leather, paper, within paints and coatings, in cosmetics, and in food additives. Currently, pigments and colorants produced through plants and microbes are the primary source exploited by modern industries. Among the other non-conventional sources, filamentous fungi particularly ascomycetous and basidiomycetous fungi (mushrooms), and lichens (symbiotic association of a fungus with a green alga or cyanobacterium) are known to produce an extraordinary range of colors including several chemical classes of pigments such as melanins, azaphilones, flavins, phenazines, and quinines. This review seeks to emphasize the opportunity afforded by pigments naturally found in fungi as a viable green alternative to current sources. This review presents a comprehensive discussion on the capacity of fungal resources such as endophytes, halophytes, and fungi obtained from a range or sources such as soil, sediments, mangroves, and marine environments. A key driver of the interest in fungi as a source of pigments stems from environmental factors and discussion here will extend on the advancement of greener extraction techniques used for the extraction of intracellular and extracellular pigments. The search for compounds of interest requires a multidisciplinary approach and techniques such as metabolomics, metabolic engineering and biotechnological approaches that have potential to deal with various challenges faced by pigment industry.

Current application of electrical pre-treatment for enhanced microalgal biomolecules extraction

Pretreatment of microalgal biomass possessing rigid cell wall is a critical step for enhancing the efficiency of microalgal biorefinery. However, the conventional pretreatment processes suffer the drawbacks of complex processing steps, long processing time, low conversion efficiency and high processing costs. This significantly hinders the industrial applicability of microalgal biorefinery. The innovative electricity-aid pretreatment techniques serve as a promising processing tool to extensively enhance the release of intracellular substances from microalgae. In this review, application of electric field-based techniques and recent advances of using electrical pretreatments on microalgae cell focusing on pulsed electric field, electrolysis, high voltage electrical discharges and moderate electric field are reviewed. In addition, the emerging techniques integrating electrolysis with liquid biphasic flotation process as promising downstream approach is discussed. This review delivers broad knowledge of the present significance of the application of these methods focusing on the development of electric assisted biomolecules extraction from microalgae.

Two-step procedure for selective recovery of bio-molecules from microalga Nannochloropsis oculata assisted by high voltage electrical discharges

Two-step procedure with the initial aqueous extraction from raw microalgae Nannochloropsis oculata and secondary organic solvent extraction from vacuum dried (VD) microalgae were applied for selective recovery of bio-molecules. The effects of preliminary aqueous washing and high voltage electrical discharges (HVED, 40 kV/cm, 4 ms pulses) were tested. The positive effects of HVED treatment and washing on selectivity of aqueous extraction of ionics and other water-soluble compounds (carbohydrates, proteins and pigments) were observed. Moreover, the HVED treatment allowed improving the kinetic of vacuum drying, and significant effects of HVED treatment on organic solvent extraction of chlorophylls, carotenoids and lipids were determined. The proposed two-step procedure combining the preliminary washing, HVED treatment and aqueous/organic solvents extraction steps are useful for selective extraction of different bio-molecules from microalgae biomass.

Bio-refinery of Chlorella sorokiniana with pulsed electric field pre-treatment

The aim of this work was to investigate the potential of PEF technology for green extraction of microalgal pigments and lipids from fresh Chlorella sorokiniana suspensions. Efficiencies of PEF treatment and different solvent systems application to C.sorokiniana were compared to efficiencies of untreated biomass extraction. Differences in chlorophyll extraction of untreated and PEF treated C.sorokiniana were only seen at short extraction times. Beneficial PEF-effect was minimised for long-time extractions of larger algae quantities where yields aligned. Extraction attempts on C. sorokiniana lipids did not show increased extractability after PEF treatment, which underlined the statement of PEF representing a rather ineffective disruption method for microalgae holding rigid cell walls.

Pulsed electric field-assisted extraction of valuable compounds from microorganisms

Microorganisms (bacteria, yeast, and microalgae) are a promising resource for products of high value such as nutrients, pigments, and enzymes. The majority of these compounds of interest remain inside the cell, thus making it necessary to extract and purify them before use. This review presents the challenges and opportunities in the production of these compounds, the microbial structure and the location of target compounds in the cells, the different procedures proposed for improving extraction of these compounds, and pulsed electric field (PEF)-assisted extraction as alternative to these procedures. PEF is a nonthermal technology that produces a precise action on the cytoplasmic membrane improving the selective release of intracellular compounds while avoiding undesirable consequences of heating on the characteristics and purity of the extracts. PEF pretreatment with low energetic requirements allows for high extraction yields. However, PEF parameters should be tailored to each microbial cell, according to their structure, size, and other factors affecting efficiency. Furthermore, the recent discovery of the triggering effect of enzymatic activity during cell incubation after electroporation opens up the possibility of new implementations of PEF for the recovery of compounds that are bounded or assembled in structures. Similarly, PEF parameters and suspension storage conditions need to be optimized to reach the desired effect. PEF can be applied in continuous flow and is adaptable to industrial equipment, making it feasible for scale-up to large processing capacities.

Extraction of valuable compounds from Arthrospira platensis using pulsed electric field treatment

Pulsed electric field (PEF) treatment was evaluated for phycocyanin and proteins extraction from Arthrospira platensis (Spirulina platensis). PEF extractions were performed using different specific energies (28, 56 and 122 J·ml^-1 of suspension) and the results were compared to the extraction with bead milling. At highest PEF-treatment energies a damage of the cell morphology could be observed and the highest yields (up to 85.2 ± 5.7 mg·g^-1 and 48.4 ± 4.4 g·100 g^-1 of phycocyanins and proteins, respectively) could be obtained at 122 and 56 J·ml^-1. The yields increased with incubation time after PEF-treatment. The antioxidant capacity of the extracts obtained after PEF-treatment was higher than of those obtained after bead milling. PEF treatment is a promising technology to obtain blue-green antioxidant extracts from A. platensis in an environmental friendly process.

A chemometric approach to evaluate the impact of pulses, Chlorella and Spirulina on proximate composition, amino acid, and physicochemical properties of turkey burgers

BACKGROUND

Changes in physicochemical parameters, proximate composition, amino acid and taste profiles of turkey burgers enriched by 1% with soy (control), pulses, Chlorella and Spirulina proteins were studied.

RESULTS

Color parameters, pH, ash content, total, essential and non-essential amino acids were significantly different among the different types of turkey burgers prepared. In this regard, turkey burgers made with pea protein presented the highest values for pH and lightness, whereas the samples prepared with broad bean showed the highest redness. The inclusion of bean and seaweed produced a marked increase of glutamic acid, lysine and aspartic acid. However, the taste profile was similar in the different six turkey burgers studied (soy, pea, lentil, broad bean, Chlorella and Spirulina protein). Orthogonal projections to latent structures discriminant analysis (OPLS-DA) allowed to classify turkey burgers according to protein sources, as compared to soy (control). Textural parameters, moisture and color were found to be the most discriminant parameters, able to describe the differences among burgers. Nonetheless, according to the supervised OPLS model, broad beans were found to possess a similar profile to soy (control).

CONCLUSION

Considering all studied parameters, the enrichment of turkey burgers with bean proteins could be used as a promising alternative to soy proteins from a technological point of view. © 2019 Society of Chemical Industry.

Incubation time after pulsed electric field treatment of microalgae enhances the efficiency of extraction processes and enables the reduction of specific treatment energy

Pulsed Electric Field (PEF) pre-treatment, applied on fresh microalgae Auxenochlorella protothecoides, induces spontaneous release of a substantial water fraction and enables subsequent lipid extraction using ethanol-hexane blends. In this study, fresh microalgae suspensions were treated with PEF and incubated under inert conditions. Incubation promotes the release of ions and carbohydrates and increases the yields of subsequent lipid extraction thus enabling a considerable reduction of PEF-treatment energy. With a 20 h incubation period at 25 °C, almost total lipid extraction is achieved with a specific PEF-treatment energy of only 0.25 MJ/kg_DW. Incubation on ice remains beneficial but less efficient than at 25 °C. Additionally, incubating microalgae cells in suspension at 100g_DW/L or in a dense paste, was almost equally efficient. Correlation between the different results suggests that spontaneous release of ions and carbohydrates facilitates more successful lipid extraction. A direct causality between the two phenomena remains to be demonstrated.

Emerging techniques for cell disruption and extraction of valuable bio-molecules of microalgae Nannochloropsis sp

Microalgae of Nannochloropsis sp. present valuable source of bio-molecules (pigments, lipids, proteins) that have nutritional potential for the prevention and treatment of human diseases. Moreover, some species of Nannochloropsis are the promising sources of biofuels and excellent candidates for the replacement of classical biofuel crops. This review describes and compares the efficiency of different conventional and novel techniques that can be used for cell disruption and recovery of bio-molecules from Nannochloropsis sp. Classification of different extraction techniques includes chemical, enzymatic, mechanical and other physical methods. The detailed analysis of extraction efficiency assisted by pressure and temperature (subcritical and supercritical fluids, hydrothermal liquefaction), ultrasound, microwaves, and pulsed electric energy (pulsed electric fields and high voltage electrical discharges) is presented. The general discussion includes comparison between techniques, their effectiveness for cell disruption and selectivity of bio-molecules extraction from Nannochloropsis sp. The cost-effectiveness, benefits and limitations of different techniques are also analyzed.