Ultrasound-assisted green solvent extraction of high-added value compounds from microalgae Nannochloropsis spp

Alternative green solvents associated with ultrasound-assisted extraction: A green chemistry approach for the extraction of carotenoids and chlorophylls from microalgae

This study proposes a method for the ultrasonic extraction of carotenoids and chlorophyll from Scenedesmus obliquus and Arthrospira platensis microalgae with green solvents. Ethanol and ethanolic solutions of ionic liquids were tested with a variety of extraction parameters, including number of extractions, time of extraction, and solid-liquid ratio R(S/L), to determine the optimal conditions. After selecting the most effective green solvent (ethanol), the process conditions were established: R(S/L) of 1:10, three extraction cycles at 3 min each), giving an extraction yield of 2602.36 and 764.21 μgcarotenoids.gdried biomass-1; and 22.01 and 5.81 mgchlorophyll.gdried biomass-1 in S. obliquus and A. platensis, respectively. The carotenoid and chlorophyll extracts obtained using ethanol were shown to be potent scavengers of peroxyl radical, being 5.94 to 26.08 times more potent α-tocopherol. These findings pave the way for a green strategy for valorizing microalgal biocompounds through efficient and environmentally friendly technological processes.

Effect of Salt Stress on the Phenolic Compounds, Antioxidant Capacity, Microbial Load, and In Vitro Bioaccessibility of Two Microalgae Species (Phaeodactylum tricornutum and Spirulina platensis)

Microalgae have gained attention as alternative food sources due to their nutritional value and biological effects. This study investigated the effect of salt stress on the antioxidant activity, phenolic profile, bioavailability of bioactive compounds, and microbial counts in the blue-green algae Spirulina platensis and diatom species Phaeodactylum tricornutum. These microalgae were cultured in growth mediums with different salt concentrations (15-35‱) We observed the highest antioxidant activity and phenolic compounds in the control groups. S. platensis (20‱) exhibited higher antioxidant activity compared to P. tricornutum (30‱), which decreased with increasing salt stress. Using HPLC-DAD-ESI-MS/MS, we identified and quantified 20 and 24 phenolic compounds in the P. tricornutum and S. platensis culture samples, respectively. The bioavailability of these compounds was assessed through in vitro digestion with the highest amounts observed in the intestinal phase. Salt stress negatively affected the synthesis of bioactive substances. Microbial counts ranged from 300 to 2.78 × 104 cfu/g for the total aerobic mesophilic bacteria and from 10 to 1.35 × 104 cfu/g for yeast/mold in P. tricornutum samples while the S. platensis samples had microbial counts from 300 to 1.9 × 104 cfu/g and the total aerobic mesophilic bacteria from 10 to 104 cfu/g, respectively. This study suggests that adding salt at different ratios to the nutrient media during the production of P. tricornutum and S. platensis can impact phenolic compounds, antioxidant capacity, microbial load evaluation, and in vitro bioaccessibility of the studied microalgae.

Extraction of Nannochloropsis Fatty Acids Using Different Green Technologies: The Current Path

Nannochloropsis is a genus of microalgae widely recognized as potential sources of distinct lipids, particularly polyunsaturated fatty acids (PUFA). These may be obtained through extraction, which has conventionally been performed using hazardous organic solvents. To substitute such solvents with "greener" alternatives, several technologies have been studied to increase their extraction potential. Distinct technologies utilize different principles to achieve such objective; while some aim at disrupting the cell walls of the microalgae, others target the extraction per se. While some methods have been utilized independently, several technologies have also been combined, which has proven to be an effective strategy. The current review focuses on the technologies explored in the last five years to extract or increase extraction yields of fatty acids from Nannochloropsis microalgae. Depending on the extraction efficacy of the different technologies, distinct types of lipids and/or fatty acids are obtained accordingly. Moreover, the extraction efficiency may vary depending on the Nannochloropsis species. Hence, a case-by-case assessment must be conducted in order to ascertain the most suited technology, or tailor a specific one, to be applied to recover a particular fatty acid (or fatty acid class), namely PUFA, including eicosapentaenoic acid.

Smart systems in producing algae-based protein to improve functional food ingredients industries

Production and extraction systems of algal protein and handling process of functional food ingredients need to control several parameters such as temperature, pH, intensity, and turbidity. Many researchers have investigated the Internet of Things (IoT) approach for enhancing the yield of microalgae biomass and machine learning for identifying and classifying microalgae. However, there have been few specific studies on using IoT and artificial intelligence (AI) for production and extraction of algal protein as well as functional food ingredients processing. In order to improve the production of algal protein and functional food ingredients, the implementation of smart system is a must to have real-time monitoring, remote control system, quick response to sudden events, prediction and characterisation. Techniques of IoT and AI are expected to help functional food industries to have a big breakthrough in the future. Manufacturing and implementation of beneficial smart systems are important to provide convenience and to increase the efficiency of work by using the interconnectivity of IoT devices to have good capturing, processing, archiving, analyzing, and automation. This review investigates the possibilities of implementation of IoT and AI in production and extraction of algal protein and processing of functional food ingredients.

Emerging trends in the pretreatment of microalgal biomass and recovery of value-added products: A review

Microalgae are a promising source of raw material (i.e., proteins, carbohydrates, lipids, pigments, and micronutrients) for various value-added products and act as a carbon sink for atmospheric CO₂. The rigidity of the microalgal cell wall makes it difficult to extract different cellular components for its applications, including biofuel production, food and feed supplements, and pharmaceuticals. To improve the recovery of products from microalgae, pretreatment strategies such as biological, physical, chemical, and combined methods have been explored to improve whole-cell disruption and product recovery efficiency. However, the diversity and uniqueness of the microalgal cell wall make the pretreatment process more species-specific and limit its large-scale application. Therefore, advancing the currently available technologies is required from an economic, technological, and environmental perspective. Thus, this paper provides a state-of-art review of the current trends, challenges, and prospects of sustainable microalgal pretreatment technologies from a microalgae-based biorefinery concept.

Microalgae biomass deconstruction using green solvents: Challenges and future opportunities

Microalgae enablefixation of CO₂into carbohydrates, lipids, and proteins through inter and intracellularly biochemical pathways. These cellular components can be extracted and transformed into renewable energy, chemicals, and materials through biochemical and thermochemical transformation processes.However, recalcitrant cell wall andlack of environmentally benign efficient pretreatment processes are key obstacles in the commercialization of microalgal biorefineries.Thus,current article describes the microalgal chemical structure, type, and structural rigidity and summarizes the traditional pretreatment methods to extract cell wall constituents. Green solvents such as ionic liquid (ILs), deep eutectic solvents (DES), and natural deep eutectic solvents (NDESs) have shown interesting solvent characteristics to pretreat biomass with selective biocomponent extraction from microalgae. Further research is needed in task-specific IL/DES design, cation-anion organization, structural activity understanding of ILs-biocomponents, environmental toxicity, biodegradability, and recyclability for deployment of carbon-neutral technologies. Additionally, coupling the microalgal industry with biorefineries may facilitate waste management, sustainability, and gross revenue.

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.

Effect of the Application of Hydrolysate of Chlorella vulgaris Extracted by Different Techniques on the Growth of Pelargonium × hortorum

The extraction method used to obtain biologically active compounds from microalgal biomass may affect the biostimulant capacity of the microalgae. The objective of this assay was to determine the most efficient extraction method to release the active components of the biomass of Chlorella vulgaris (C. vulgaris). Plantlets of Pelargonium × hortorum were grown in a greenhouse and five treatments were applied: C-application with water; M-application with untreated C. vulgaris microalgae; M-US-application with C. vulgaris microalgae treated with ultrasound; M-USHY-application with C. vulgaris microalgae treated with ultrasound and enzymatic hydrolysis; and M-USHYAU-application with C. vulgaris microalgae treated with ultrasound, enzymatic hydrolysis, and autoclaving. All microalgae treatments increased shoot number and stem and plant diameter. The US-treated biomass increased the inflorescence of the plant significantly compared to the control. To extract bioactive compounds from eukaryotic microalgae for plant biostimulating purposes, the US-treatment (or any other method damaging the plasma membrane) of microalgae cell is, or seems to be, suitable.. Macronutrient content in leaves was not affected by the microalgae treatment, except for K.

Carotenoids Biosynthesis, Accumulation, and Applications of a Model Microalga Euglenagracilis

The carotenoids, including lycopene, lutein, astaxanthin, and zeaxanthin belong to the isoprenoids, whose basic structure is made up of eight isoprene units, resulting in a C40 backbone, though some of them are only trace components in Euglena. They are essential to all photosynthetic organisms due to their superior photoprotective and antioxidant properties. Their dietary functions decrease the risk of breast, cervical, vaginal, and colorectal cancers and cardiovascular and eye diseases. Antioxidant functions of carotenoids are based on mechanisms such as quenching free radicals, mitigating damage from reactive oxidant species, and hindering lipid peroxidation. With the development of carotenoid studies, their distribution, functions, and composition have been identified in microalgae and higher plants. Although bleached or achlorophyllous mutants of Euglena were among the earliest carotenoid-related microalgae under investigation, current knowledge on the composition and biosynthesis of these compounds in Euglena is still elusive. This review aims to overview what is known about carotenoid metabolism in Euglena, focusing on the carotenoid distribution and structure, biosynthesis pathway, and accumulation in Euglena strains and mutants under environmental stresses and different culture conditions. Moreover, we also summarize the potential applications in therapy preventing carcinogenesis, cosmetic industries, food industries, and animal feed.

Ultrasound for microalgal cell disruption and product extraction: A review

Microalgae are a promising feedstock for the production of biofuels, nutraceuticals, pharmaceuticals and cosmetics, due to their superior capability of converting solar energy and CO₂ into lipids, proteins, and other valuable bioactive compounds. To facilitate the release of these important biomolecules from microalgae, effective cell disruption is usually necessary, where the use of ultrasound has gained tremendous interests as an alternative to traditional methods. This review not only summarizes the mechanisms of and operation parameters affecting cell disruption, but also takes an insight into measuring techniques, synergistic integration with other disruption methods, and challenges of ultrasonication for microalgal biorefining. Optimal conditions including ultrasonic frequency, intensity, and duration, and liquid viscosity and sonochemical reactor are the key factors for maximizing the disruption and extraction efficiency. A combination of ultrasound with other disruption methods such as ozonation, microwave, homogenization, enzymatic lysis, and solvents facilitates cell disruption and release of target compounds, thus provides powerful solutions to commercial scale-up of ultrasound extraction for microalgal biorefining. It is concluded that ultrasonication is a sustainable "green" process, but more research and work are needed to upscale this process without sacrificing performance or consuming more energy.

Microalgal Biorefinery Concepts’ Developments for Biofuel and Bioproducts: Current Perspective and Bottlenecks

Microalgae have received much interest as a biofuel feedstock. However, the economic feasibility of biofuel production from microalgae does not satisfy capital investors. Apart from the biofuels, it is necessary to produce high-value co-products from microalgae fraction to satisfy the economic aspects of microalgae biorefinery. In addition, microalgae-based wastewater treatment is considered as an alternative for the conventional wastewater treatment in terms of energy consumption, which is suitable for microalgae biorefinery approaches. The energy consumption of a microalgae wastewater treatment system (0.2 kW/h/m³) was reduced 10 times when compared to the conventional wastewater treatment system (to 2 kW/h/m³). Microalgae are rich in various biomolecules such as carbohydrates, proteins, lipids, pigments, vitamins, and antioxidants; all these valuable products can be utilized by nutritional, pharmaceutical, and cosmetic industries. There are several bottlenecks associated with microalgae biorefinery. Hence, it is essential to promote the sustainability of microalgal biorefinery with innovative ideas to produce biofuel with high-value products. This review attempted to bring out the trends and promising solutions to realize microalgal production of multiple products at an industrial scale. New perspectives and current challenges are discussed for the development of algal biorefinery concepts.

Environmentally Friendly Techniques for the Recovery of Polyphenols from Food By-Products and Their Impact on Polyphenol Oxidase: A Critical Review

Even though food by-products have many negative financial and environmental impacts, they contain a considerable quantity of precious bioactive compounds such as polyphenols. The recovery of these compounds from food wastes could diminish their adverse effects in different aspects. For doing this, various nonthermal and conventional methods are used. Since conventional extraction methods may cause plenty of problems, due to their heat production and extreme need for energy and solvent, many novel technologies such as microwave, ultrasound, cold plasma, pulsed electric field, pressurized liquid, and ohmic heating technology have been regarded as alternatives assisting the extraction process. This paper highlights the competence of mild technologies in the recovery of polyphenols from food by-products, the effect of these technologies on polyphenol oxidase, and the application of the recovered polyphenols in the food industry.

Extraction, Purification and In Vitro Antioxidant Activity Evaluation of Phenolic Compounds in California Olive Pomace

Olive pomace (OP) is a valuable food byproduct that contains natural phenolic compounds with health benefits related to their antioxidant activities. Few investigations have been conducted on OP from the United States while many studies on European OP have been reported. OP of Arbequina, the most common cultivar from California, was collected and extracted by water, 70% methanol and 70% ethanol, followed by purification using macroporous absorbing resin. Results showed that the extractable total phenolic content (TPC) was 36–43 mg gallic acid equivalents (GAE)/g in pitted, drum-dried defatted olive pomace (DOP), with major contributions from hydroxytyrosol, oleuropein, rutin, verbascoside, 4-hydroxyphenyl acetic acid, hydroxytyrosol-glucoside and tyrosol-glucoside. Macroporous resin purification increased TPC by 4.6 times the ethanol crude extracts of DOP, while removing 37.33% total sugar. The antioxidant activities increased 3.7 times Trolox equivalents (TrE) by DPPH and 4.7 times TrE by ferric reducing antioxidant power (FRAP) in the resin purified extracts compared to the ethanol crude extracts. This study provided a new understanding of the extraction of the bioactive compounds from OP which could lead to practical applications as natural antioxidants, preservatives and antimicrobials in clean-label foods in the US.

Supercritical fluid extraction (SCFE) as green extraction technology for high-value metabolites of algae, its potential trends in food and human health

Application of high-value algal metabolites (HVAMs) in cosmetics, additives, pigments, foods and medicines are very important. These HVAMs can be obtained from the cultivation of micro- and macro-algae. These metabolites can benefit human and animal health in a physiological and nutritional manner. However, because of conventional extraction methods and their energy and the use of pollutant solvents, the availability of HVAMs from algae remains insufficient. Receiving their sustainability and environmental benefits have recently made green extraction technologies for HVAM extractions more desirable. But very little information is available about the technology of green extraction of algae from these HVAM. This review, therefore, highlights the supercritical fluid extraction (SCFE) as principal green extraction technologyand theirideal parameters for extracting HVAMs. In first, general information is provided concerning the HVAMs and their components of macro and micro origin. The review also includes a description of SCFE technology's properties, instrumentation operation, solvents used, and the merits and demerits. Moreover, there are several HVAMs associated with their numerous high-level biological activities which include high-level antioxidant, anti-inflammatory, anticancer and antimicrobial activity and have potential health-beneficial effects in humans since they are all HVAMs, such as foods and nutraceuticals. Finally, it provides future insights, obstacles, and suggestions for selecting the right technologies for extraction.

Experimental and Theoretical Screening for Green Solvents Improving Sulfamethizole Solubility

Solubility enhancement of poorly soluble active pharmaceutical ingredients is of crucial importance for drug development and processing. Extensive experimental screening is limited due to the vast number of potential solvent combinations. Hence, theoretical models can offer valuable hints for guiding experiments aimed at providing solubility data. In this paper, we explore the possibility of applying quantum-chemistry-derived molecular descriptors, adequate for development of an ensemble of neural networks model (ENNM), for solubility computations of sulfamethizole (SMT) in neat and aqueous binary solvent mixtures. The machine learning procedure utilized information encoded in σ-potential profiles computed using the COSMO-RS approach. The resulting nonlinear model is accurate in backcomputing SMT solubility and allowed for extensive screening of green solvents. Since the experimental characteristics of SMT solubility are limited, the data pool was extended by new solubility measurements in water, five neat organic solvents (acetonitrile, N,N-dimethylformamide, dimethyl sulfoxide, 1,4-dioxane, and methanol), and their aqueous binary mixtures at 298.15, 303.15, 308.15, and 313.15 K. Experimentally determined order of decreasing SMT solubility in neat solvents is the following: N,N-dimethylformamide > dimethyl sulfoxide > methanol > acetonitrile > 1,4dioxane >> water, in all studied temperatures. Similar trends are observed for aqueous binary mixtures. Since N,N-dimethylformamide is not considered as a green solvent, the more acceptable replacers were searched for using the developed model. This step led to the conclusion that 4-formylmorpholine is a real alternative to N,N-dimethylformamide, fulfilling all requirements of both high dissolution potential and environmental friendliness.

Insights into diatom microalgal farming for treatment of wastewater and pretreatment of algal cells by ultrasonication for value creation

Wastewater management and its treatment have revolutionized the industry sector into many innovative techniques. However, the cost of recycling via chemical treatment has major issues especially in economically poor sectors. On the offset, one of the most viable and economical techniques to clean wastewater is by growing microalgae in it. Since wastewater is rich in nitrates, phosphates and other trace elements, the environment is suitable for the growth of microalgae. On the other side, the cost of harvesting microalgae for its secondary metabolites is burgeoning. While simultaneously growing of microalgae in photobioreactors requires regular feeding of the nutrients and maintenance which increases the cost of operation and hence cost of its end products. The growth of microalgae in waste waters makes the process not only economical but they also manufacture more amounts of value added products. However, harvesting of these values added products is still a cumbersome task. On the offset, it has been observed that pretreating the microalgal biomass with ultrasonication allows easy oozing of the secondary metabolites like oil, proteins, carbohydrates and methane at much lower cost than that required for their extraction. Among microalgae diatoms are more robust and have immense crude oil and are rich in various value added products. However, due to their thick silica walls they do not ooze the metabolites until the mechanical force on their walls reaches certain threshold energy. In this review recycling of wastewater using microalgae and its pretreatment via ultrasonication with special reference to diatoms is critically discussed. Perspectives on circular bioeconomy and knowledge gaps for employing microalgae to recycle wastewater have been comprehensively narrated.

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 optimization of bioactive compounds from ora-pro-nobis (Pereskia aculeata Miller) leaves and their in vitro antioxidant and antihemolytic activities

Ora-pro-nobis (Pereskia aculeata Miller) is a non-conventional food plant common in Brazil. The objective of this study was to optimize the extraction of bioactive phenolic compounds from ora-pro-nobis leaves by employing solvent mixtures. Ten extracts were obtained with water, ethanol, acetone, and their binary and ternary mixtures, evaluating the chemical composition, antioxidant activity and bioactivities in vitro. The response surface methodology was applied to model the results and calculate the optimal solvent composition, which is 60% water, 40% ethanol and 0% acetone. The optimized extract is rich in phenolic compounds (64 mg GAE/g) and proteins (823 mg/g) and presents antioxidant activity (in intracellular media as well) and inhibits lipid peroxidation (32%) along with hypotonic hemolysis (H₅₀ = 0.339%), it does not present toxicity in vitro against cancer and normal cells. This is the first report of chicoric, caffeoyl-hexaric and coumaroyl-hexaric acids and some glycosylate derivatives of flavonols in ora-pro-nobis leaves.

Comparison and optimization of conventional and ultrasound-assisted solvent extraction for synthetization of lemongrass (Cymbopogon)-infused cooking oil

The lemongrass plant, which is widely cultivated in Asia, Australia, and Africa, has been reported to have many significant health benefits such as antimicrobial, insecticide, anticancer, fight fever, and disinfection. Therefore, it is an added benefit to have lemongrass compounds in cooking oil. This study was aimed to compare the conventional (CSE), and ultrasound-assisted solvent extraction (UASE) for citral compounds from lemongrass (Cymbopogon) leaves and to optimize the best extraction method using the response surface methodology (RSM) and ANOVA. RSM design of experiments using three types of cooking oils; palm oil, sunflower oil, and corn oil. The effect of three independent variables, which are temperature (48.2-81.8°C), extraction time (4.8-55.2 min), and solvent to leaves ratio (5.3-18.7), was investigated. The characterization of lemongrass-infused cooking oil was evaluated by Fourier transform infrared spectroscopy (FT-IR), Gas Chromatography-Mass Spectrometry (GC-MS) and Scanning Electron Microscopy (SEM) analysis for confirmation of the citral compound extraction. This extraction process is optimized using Response Surface Methodology (RSM) for producing the lemongrass-infused cooking oil. After optimization, the UASE process gives 1.009 × 106 maximum citral area for palm oil and 1.767 × 106 maximum citral area for sunflower oil. CSE process only can give 2.025 × 105 and 2.179 × 105 citral area in the GC-MS spectrum for palm oil and sunflower oil respectively. For both the UASE and the CSE, the optimum operating conditions are 81.8°C of extraction temperature and 55.2 min of extraction time except for lemongrass-infused palm oil in the CSE process with 45 min extraction time. The optimum solvent to leaves ratio varies from 5.3:1 to 12.9:1. This study found that corn oil cannot be used as a solvent to extract lemongrass-infused cooking oil due to the insignificant changes and no citral peak. The lemongrass (Cymbopogon)-infused palm oil and sunflower oil extracted using the UASE have a higher maximum citral area than the CSE process.

Development of an aqueous ultrasound-assisted extraction process of bioactive compounds from beet leaves: a proposal for reducing losses and increasing biomass utilization

BACKGROUND

Red beet plants are cultivated worldwide for the consumption of their roots, generating large amounts of unexploited by-products. In particular, beet leaves (BLs) represent about 50% of the whole plant and are usually discarded as waste. This constitutes not only an economic issue, since multiple resources invested in the production will be wasted, but also an environmental problem because of the pollution associated with their disposal. However, BLs comprise an important source of functional compounds (polyphenols and betalains) that could be recovered from the raw material, representing a sustainable solution for the underutilization of this by-product. This study proposes the recovery of polyphenols and betalains using an aqueous ultrasound-assisted extraction (UAE) process at different powers (35, 50, and 100 W) that was characterized and optimized.

RESULTS

UAE significantly enhanced the recovery of bioactive compounds and shortened the time required for extraction in comparison with traditional macerations (35 < 50 < 100 W). During UAE, the temperature of the systems increased as a function of the power applied, favouring the recovery of these phytochemicals. Additionally, a Box-Behnken design and response surface methodology were employed to optimize UAE conditions (90 W ultrasound power, 1:20 solid:liquid ratio, 16 min extraction time), under which the yields were 14.9 mg g^-1 (polyphenols), 949.1 μg g^-1 (betaxanthins), and 562.2 μg g^-1 (betacyanins), consistent with the values predicted by the models.

CONCLUSION

This study enabled the development of a green-solvent UAE process that constitutes an effective post-harvest by-products strategy to minimize losses and increase biomass utilization through the recovery of bioactive compounds from BLs, promoting sustainability in the agri-food chain. © 2020 Society of Chemical Industry.

Progress in ultrasound-assisted extraction of the value-added products from microorganisms

Extracting value-added products from microorganisms is an important research focus for the future. Among the many extraction methods, ultrasound-assisted extraction (UAE) has attracted more attention owing to its advantages in reducing working time, increasing yield, and improving the quality of the extract. This review summarizes the use of UAE value-added products from microorganisms, with the main extracted substances are pigments, lipids, polysaccharides, and proteins. In addition, this work also summarizes the mechanism of UAE and highlights the factors that affect UAE operation, such as ultrasonic power intensity or power density, operation mode, and energy consumption, which need to be considered. All extraction products from microorganisms showed that UAE can effectively improve the extraction yields of value-added products. It also highlights the existing problems of the technology and possible future prospects. In general, the UAE of value-added substances from microorganisms is feasible and has the potential for development.

Mechanical Cell Disruption Technologies for the Extraction of Dyes and Pigments from Microorganisms: A Review

The production of pigments using single cell microorganisms is gaining traction as a sustainable alternative to conventional syntheses, which rely, in no negligible proportions, on petrochemicals. In addition to depending on petroleum, these syntheses involved the use of toxic organic solvents, which may be inadequately disposed of across a range of industries, thus compounding the deleterious effects of fossil fuel exploitation. Literature suggests that notable research efforts in the area of sustainable pigment production using single cell microorganisms are focused on the production of pigments coveted for their interesting qualities, which transcend their mere capacity to dye various fabrics both natural and synthetic. As interest in sustainable pigment biosynthesis grows, the need to devise effective and efficient cell disruption processes becomes more pressing given that the viability of pigment biosynthesis is not only dependent on microorganisms’ yield in terms of production, but also on researchers’ ability to recover them. This review chiefly reports findings as to mechanical cell disruption methods, used individually or in various combinations, and their aptitude to recover biosynthetic pigments.

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).

Extracellular and intracellular phenol production by microalgae during photoautotrophic batch cultivation

Understanding the mechanisms of phenol production by microalgae can contribute to the development of microalgal biorefinery processes with higher economic and environmental sustainability. However, little is known about how phenols are produced and accumulate during microalgal cultivation. In this study, both extracellular and intracellular phenol production by two microalgal strains (Tetradesmus obliquus and Chlorella sp.) were investigated throughout a conventional photoautotrophic batch cultivation. The highest intracellular phenol content (10-25 mg g^-1) and productivity (12-18 mg L^-1 d^-1) were attained for both strains in the first part of the batch, indicating a positive relation with nutrient availability and biomass productivity. Extracellular phenol production was 2-20 fold lower than intracellular phenols, but reached up to 27 mg L^-1 for T. obliquus and 13 mg L^-1 for Chlorella sp. The latter finding highlights relevant issues about the management of the exhausted culture medium, due to likely antimicrobial effects.

In-situ lipid and fatty acid extraction methods to recover viable products from Nannochloropsis sp

Nannochloropsis sp. has received increased attention by researchers in recent years due to its complexity and abundance of lipid structures. The lipids of this microalgae species have been identified to contain large quantities of neutral lipids which are capable of producing raw materials for nutraceuticals, food additives and biofuels. The production of biodiesel has received the greatest attention as there is an increase in global demand for both more fuel and more environmentally sustainable methods to produce such resources. The greatest challenges facing industries to mass produce viable products from microalgae involve the degradation of the cell wall and extracting the fatty acid of interest due to high costs. Various studies have shown that the extraction lipids from the microalgae can greatly influence the overall fatty acid composition. Different extraction methods can result in recovering higher quantities of either saturated fatty acids, monounsaturated fatty acids or polyunsaturated fatty acids. Biodiesel production requires higher quantities of saturated fatty acids and monosaturated fatty acids as increased quantities of polyunsaturated fatty acids result in oxidation which decreases the performance of the biodiesel. Whereas, polyunsaturated fatty acids are required in order to produce pharmaceuticals and food additives such as omega 3. This review will focus on how different in-situ extraction methods for lipid and fatty acid recovery, influence the fatty acid composition of various Nannochloropsis species (oculate, gaditana, salina and oceanica). The mechanical methods (microwave, ultrasonic and supercritical‑carbon dioxide) of extraction for Nannochloropsis sp. will be critically evaluated. The use of enzymes will also be addressed, for their ability to extract fatty acids in a more environmentally friendly manner. This paper will report on the viable by-products which can be produced using different extraction methods.

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.

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.

Antioxidant Properties of Agri-food Byproducts |and Specific Boosting Effects of Hydrolytic Treatments

Largely produced agri-food byproducts represent a sustainable and easily available source of phenolic compounds, such as lignins and tannins, endowed with potent antioxidant properties. We report herein the characterization of the antioxidant properties of nine plant-derived byproducts. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing/antioxidant power (FRAP) assays indicated the superior activity of pomegranate peels and seeds, grape pomace and pecan nut shell. An increase in the antioxidant potency was observed for most of the waste materials following a hydrolytic treatment, with the exception of the condensed tannin-rich pecan nut shell and grape pomace. UV-Vis and HPLC investigation of the soluble fractions coupled with the results from IR analysis and chemical degradation approaches on the whole materials allowed to conclude that the improvement of the antioxidant properties was due not only to removal of non-active components (mainly carbohydrates), but also to structural modifications of the phenolic compounds. Parallel experiments run on natural and bioinspired model phenolic polymers suggested that these structural modifications positively impacted on the antioxidant properties of lignins and hydrolyzable tannins, whereas significant degradation of condensed tannin moieties occurred, likely responsible for the lowering of the reducing power observed for grape pomace and pecan nut shell. These results open new perspectives toward the exploitation and manipulation of agri-food byproducts for application as antioxidant additives in functional materials.

Electroporation as a Solvent-Free Green Technique for Non-Destructive Extraction of Proteins and Lipids From Chlorella vulgaris

Proteins extracted from microalgae for food, personal care products and cosmetics must be of high purity, requiring solvent-free extraction techniques despite their generally considerably lower protein yield and higher energy consumption. Here, three such approaches for green extraction of proteins from Chlorella vulgaris were evaluated: ultrasound, freeze-thawing, and electroporation; chemical lysis was used as positive control (maximal achievable extraction), and no extraction treatment as negative control. Compared to chemical lysis, electroporation yielded the highest fraction of extracted protein mass in the supernatant (≤27%), ultrasound ≤24%, and freeze-thawing ≤15%. After a growth lag of several days, electroporated groups of algal cells started to exhibit growth dynamics similar to the negative control group, while no growth regeneration was detected in groups exposed to ultrasound, freeze-thawing, or chemical lysis. For electroporation as the most efficient and the only non-destructive among the considered solvent-free protein extraction techniques, simultaneous extraction of intracellular algal lipids into supernatant was then investigated by HPLC, proving relatively low-yield (≤7% of the total algal lipid mass), yet feasible for glycerides (tri-, di-, and mono-) as well as other fatty acid derivatives. Our results show that electroporation, though lower in extraction yields than chemical lysis or mechanical disintegration, is in contrast to them a technique for largely debris-free extraction of proteins from microalgae, with no need for prior concentration or drying, with feasible growth regeneration, and with potential for simultaneous extraction of intracellular algal lipids into the supernatant.

Extraction and bioprocessing with supercritical fluids

Supercritical fluid (SCF) technologies have emerged as a real alternative to various natural product extraction processes and pharmaceutical production to obtain micronized particles, coprecipitates, nanocomposite polymer structures and liposomes, in addition to other increasingly larger applications described in literature. In the present work, a brief literature review of the application of supercritical fluid extraction (SFE) is presented. This is evidenced by several publications and patents, contributions from several countries and the increase of industries around the world dedicated to this technique. Next, we aim to focus the analysis of SFE on a review of the literature applied to microalgae as a substitute primitive feedstock due to its high growth rate, valuable biologically active lipophilic substances, and photosynthetic efficiency without competition with food sources or needs of arable lands. We finally discussing an SCF bioprocess with a very new perspective for liposome production focalized on its potential at industrial scale.

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.

Progress in the physicochemical treatment of microalgae biomass for value-added product recovery

Interest in microalgae-derived products is growing, mostly due to their unique characteristics and range of industrial applications. To obtain different products, one must employ specific pretreatments that retain the properties of the biologically active compounds extracted from microalgae biomass; thus, new extraction techniques require frequent upgrades. Due to increased interest in economically viable and ecologically friendly processes, new extraction methods that can be incorporated into microalgae biorefinery systems have become the main focus of research. Therefore, this review aims to address the potential applications, future prospects, and economic scenario of the new physicochemical treatments used in the extraction of bioactive microalgae compounds.

Organic-solvent-free extraction of carotenoids from yeast Rhodotorula glutinis by application of ultrasound under pressure

The extraction of Rhodotorula glutinis carotenoids by ultrasound under pressure (manosonication) in an aqueous medium has been demonstrated. The influence of treatment time, pressure, and ultrasound amplitude on R. glutinis inactivation and on the extraction of carotenoids was evaluated, and the obtained data were described mathematically. The extraction yields were lineal functions of those three parameters, whereas inactivation responded to a more complex equation. Under optimum treatment conditions, 82% of carotenoid content was recovered. Extraction of carotenoids in an aqueous medium was attributed to the capacity of ultrasound for cell disruption and emulsification. Cavitation caused the rupture of cell envelopes and the subsequent formation of small droplets of carotenoids surrounded by the phospholipids of the cytoplasmic membrane that would stabilize the emulsion. Analysis of the dispersed particle size of the extracts demonstrated that a fine, homogeneous emulsion was formed after treatment (average size: 230 nm; polydispersity <0.22). This research describes an innovative green process for extracting carotenoids from fresh biomass of R. glutinis in which only two unit operations are required: ultrasonic treatment, followed by a centrifugation step to discard cell debris. The extract obtained thanks to this procedure is rich in carotenoids (25 mg/L) and could be directly incorporated as a pigment in foods, beverages, and diet supplements; it can also be utilized as an ingredient in drugs or cosmetics.

Rational design, synthesis, adsorption principles and applications of metal oxide adsorbents: a review

The shortage of water resources and increasingly serious water pollution have driven the development of high-efficiency water treatment technology. Among a variety of technologies, adsorption is widely used in environmental remediation. As a class of typical adsorbents, metal oxides have been developed for a long time and continued to attract widespread attention, since they have unique physicochemical properties, including abundant surface active sites, high chemical stability, and adjustable shape and size. In this review, the basic principles of the adsorption process will be first elucidated, including affecting factors, evaluation index, adsorption mechanisms, and common kinetic and isotherm models. Then, the adsorption properties of several typical metal oxides, and key parameters affecting the adsorption performance such as particle/pore size, morphology, functionalization and modification, supports and calcination temperature will be discussed, as well as their application in the removal of various inorganic and organic contaminants. In addition, desorption and recycling of the spent adsorbent are summarized. Finally, the future development of metal oxide based adsorbents is also discussed.

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.

Ultrasound-Assisted Extraction Optimization of Phenolic Compounds from Citrus latifolia Waste for Chitosan Bioactive Nanoparticles Development

Bioactive Phenols-loaded chitosan nanoparticles (PL-CNps) were developed by ionic gelation from Persian lemon (Citrus latifolia) waste (PLW) and chitosan nanoparticles. Response Surface Methodology (RSM) was used to determine the optimal Ultrasound-Assisted Extraction (UAE) conditions for the total phenolic compounds (TPC) recovery from PLW (58.13 mg GAE/g dw), evaluating the ethanol concentration, extraction time, amplitude, and solid/liquid ratio. Eight compounds expressed as mg/g dry weight (dw) were identified by ultra-performance liquid chromatography coupled photo diode array (UPLC-PDA) analysis: eriocitrin (20.71 ± 0.09), diosmin (18.59 ± 0.13), hesperidin (7.30 ± 0.04), sinapic acid (3.67 ± 0.04), catechin (2.92 ± 0.05), coumaric acid (2.86 ± 0.01), neohesperidin (1.63 ± 0.00), and naringenin (0.44 ± 0.00). The PL-CNps presented size of 232.7 nm, polydispersity index of 0.182, Z potential of -3.8 mV, and encapsulation efficiency of 81.16%. The results indicated that a synergic effect between phenolic compounds from PLW and chitosan nanoparticles was observed in antioxidant and antibacterial activity, according to Limpel's equation. Such results indicate that PLW in such bioprocesses shows excellent potential as substrates for the production of value-added compounds with a special application for the food industry.