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.     

Mixotrophic Cultivation of Microalgae for Biodiesel Production: Status and Prospects

Biodiesel from microalgae provides a promising alternative for biofuel production. Microalgae can be produced under three major cultivation modes, namely photoautotrophic cultivation, heterotrophic cultivation, and mixotrophic cultivation. Potentials and practices of biodiesel production from microalgae have been demonstrated mostly focusing on photoautotrophic cultivation; mixotrophic cultivation of microalgae for biodiesel production has rarely been reviewed. This paper summarizes the mechanisms and virtues of mixotrophic microalgae cultivation through comparison with other major cultivation modes. Influencing factors of microalgal biodiesel production under mixotrophic cultivation are presented, development of combining microalgal biodiesel production with wastewater treatment is especially reviewed, and bottlenecks and strategies for future commercial production are also identified.     

Low n-6/n-3 Gestation and Lactation Diets Influence Early Performance,Muscle and Adipose Polyunsaturated Fatty Acid Content and Deposition,and Relative Abundance of Proteins in Suckling Piglets

Elevated omega-6 (n-6) and omega-3 (n-3) polyunsaturated fatty acids (PUFAs) ratios in swine diets can potentially impose a higher risk of inflammatory and metabolic diseases in swine. A low ratio between the two omega PUFAs has beneficial effects on sows’ and piglets’ production performance and immunity status. At present, there are few studies on how sow nutrition directly affects the protein and fat deposition in suckling piglets. Two groups of sows were fed diets with high or low n-6/n-3 polyunsaturated ratios of 13:1 (SOY) and 4:1 (LIN), respectively, during gestation and lactation. Longissimus dorsi muscle and adipose tissue from newborn piglets, nourished only with sow’s milk, were subjected to fatty acid profiling by gas chromatography–mass spectrometry (GC-MS) and to proteomics assays based on nano-liquid chromatography coupled to high-resolution tandem mass spectrometry (nLC-HRMS). Fatty acid profiles on both muscle and adipose tissues resembled the magnitude of the differences between fatty acid across diets. Proteomic analysis revealed overabundance of 4 muscle and 11 adipose tissue proteins in SOY compared to LIN in both piglet tissues. The detected overabundance of haptoglobin, an acute-phase protein, and the stimulation of protein-coding genes and proteins related to the innate immune response and acute inflammatory response could be associated with the pro-inflammatory role of n-6 PUFAs.     

Chemical Characterization,Antiproliferative and Antioxidant Activities of Polyunsaturated Fatty Acid-Rich Extracts from Chlorella sp. S14

Microalgae is a rich source of polyunsaturated fatty acid. This study was conducted to identify and isolate microalgal strain with the potentials for producing polyunsaturated fatty acids (PUFAs) and determine its cytotoxic effect on some cancer cells. The algal strain (Chlorella sp. S14) was cultivated using modified BG-11 media, and algal biomass obtained was used for fatty acid extraction. Gas chromatographic–mass spectrometry was used to identify and quantify the levels of the fatty acid constituents. The total content of monounsaturated fatty acids (1.12%) was low compared to polyunsaturated fatty acids (PUFAs) (52.87%). Furthermore, n-3 PUFAs accounted for (12.37%) of total PUFAs with the presence of α-linolenic acid (2.16%) and cis-11,14,17-eicosatrienoic acid (2.16%). The PUFA-rich extract did not exhibit a cytotoxic effect on normal cells. Treatment with the PUFA-rich extract (150 µg/mL) significantly reduced cell viability in MCF-7 (31.58%) and A549 (62.56%) cells after the 48 h treatment. Furthermore, treatment of MCF-7 with fatty acid extracts (125 and 150 µg/mL) showed a significant reduction in MDA levels, increase in catalase activities and decrease in GSH level compared to untreated cells. However, a slight decrease in MDA level was observed in A549 cells after the 48 h treatment. There are no significant changes in catalase activities and GSH level in treated A549 cells. However, a slight reduction of NO levels was observed in treated MCF-7 and A549 cells. These results indicate the potentials of PUFA-rich extracts from Chlorella sp. S14 to reduce viability and modulate redox status in A549 and MCF-7 cells.     

Alkaloids Used as Medicines: Structural Phytochemistry Meets Biodiversity—An Update and Forward Look

Selecting candidates for drug developments using computational design and empirical rules has resulted in a broad discussion about their success. In a previous study, we had shown that a species’ abundance [as expressed by the GBIF (Global Biodiversity Information Facility)] dataset is a core determinant for the development of a natural product into a medicine. Our overarching aim is to understand the unique requirements for natural product-based drug development. Web of Science was queried for research on alkaloids in combination with plant systematics/taxonomy. All alkaloids containing species demonstrated an average increase of 8.66 in GBIF occurrences between 2014 and 2020. Medicinal Species with alkaloids show higher abundance compared to non-medicinal alkaloids, often linked also to cultivation. Alkaloids with high biodiversity are often simple alkaloids found in multiple species with the presence of ’driver species‘ and are more likely to be included in early-stage drug development compared to ‘rare’ alkaloids. Similarly, the success of an alkaloid containing species as a food supplement (‘botanical’) is linked to its abundance. GBIF is a useful tool for assessing the druggability of a compound from a certain source species. The success of any development programme from natural sources must take sustainable sourcing into account right from the start.     

Trends on CO2 Capture with Microalgae: A Bibliometric Analysis

The alarming levels of carbon dioxide (CO₂) are an environmental problem that affects the economic growth of the world. CO₂ emissions represent penalties and restrictions due to the high carbon footprint. Therefore, sustainable strategies are required to reduce the negative impact that occurs. Among the potential systems for CO₂ capture are microalgae. These are defined as photosynthetic microorganisms that use CO₂ and sunlight to obtain oxygen (O₂) and generate value-added products such as biofuels, among others. Despite the advantages that microalgae may present, there are still technical–economic challenges that limit industrial-scale commercialization and the use of biomass in the production of added-value compounds. Therefore, this study reviews the current state of research on CO₂ capture with microalgae, for which bibliometric analysis was used to establish the trends of the subject in terms of scientometric parameters. Technological advances in the use of microalgal biomass were also identified. Additionally, it was possible to establish the different cooperation networks between countries, which showed interactions in the search to reduce CO₂ concentrations through microalgae.     

Development of a Functional Cookie Formulated with Chaya (Cnidoscolus aconitifolius (Mill.) I.M. Johnst) and Amaranth (Amaranthus cruentus)

Chaya and amaranth are Mexican traditional foods with a high nutritional value. Many studies have demonstrated the individual beneficial effect of each. However, there is no evidence of the use of these foods on the formulation of functional foods. This study evaluated the effect of replacing 5–20% of wheat flour with chaya and amaranth flours to generate four different formulations of cookies. Proximal analysis, total polyphenols and oxalate content, antioxidant activity, fatty acid profile, and sensory analysis were performed on the cookies. The results of the chemical composition showed that all cookies have a high protein content (9.21–10.10%), an adequate amount of fiber (5.34–6.63%), and a balanced ratio of unsaturated–saturated fatty acids (70:20), and they contain PUFAs (50.4–53.2 g/100 g of fatty acids), especially α-linolenic and oleic acids. All formulations presented antioxidant activity (2540 ± 65.9 to 4867 ± 61.7 Trolox equivalents (μmoles/100 g)) and polyphenols (328–790 mg/100 g); in particular, quercetin was identified in their composition. Results of the sensory analysis indicated that incorporation of chaya and amaranth flour in cookies does not affect the acceptability of the products. The inclusion of traditional foods, such as chaya and amaranth, in cookies enhances their nutritional value and increases the content of bioactive compounds associated with health effects.     

Bioactive Hydrolysates from Chlorella vulgaris: Optimal Process and Bioactive Properties

Microalgae have been described as a source of bioactive compounds, such as peptides. Microalgae are easy to produce, making them a sustainable resource for extracting active ingredients for industrial applications. Several microalgae species have interesting protein content, such as Chlorella vulgaris with around 52.2% of protein, making it promising for peptide hydrolysate production. Therefore, this work focused on the production of water-soluble hydrolysates rich in proteins/peptides from the microalgae C. vulgaris and studied bioactive properties. For that, a design of experiments (DOE) was performed to establish the optimal conditions to produce hydrolysates with higher levels of protein, as well as antioxidant and antihypertensive properties. Four experimental factors were considered (cellulase percentage, protease percentage, hydrolysis temperature, and hydrolysis duration) for three responses (protein content, antioxidant activity, and antihypertensive activity). The optimal conditions determined by the DOE allowed producing a scaled-up hydrolysate with 45% protein, with antioxidant activity, measured by oxygen radical absorbance capacity assay, of 1035 µmol TE/g protein, IC₅₀ for angiotensin-converting enzyme inhibition activity of 286 µg protein/mL, and α-glucosidase inhibition of 31% (30 mg hydrolysate/mL). The obtained hydrolysates can be used as functional ingredients for food and nutraceuticals due to their antioxidant, antihypertensive, and antidiabetic potential. Moreover, the antioxidant potential of the extracts may be relevant for the cosmetic industry, especially in antiaging formulations.     

Anthocyanins Recovered from Agri-Food By-Products Using Innovative Processes: Trends,Challenges, and Perspectives for Their Application in Food Systems

Anthocyanins are naturally occurring phytochemicals that have attracted growing interest from consumers and the food industry due to their multiple biological properties and technological applications. Nevertheless, conventional extraction techniques based on thermal technologies can compromise both the recovery and stability of anthocyanins, reducing their global yield and/or limiting their application in food systems. The current review provides an overview of the main innovative processes (e.g., pulsed electric field, microwave, and ultrasound) used to recover anthocyanins from agri-food waste/by-products and the mechanisms involved in anthocyanin extraction and their impacts on the stability of these compounds. Moreover, trends and perspectives of anthocyanins’ applications in food systems, such as antioxidants, natural colorants, preservatives, and active and smart packaging components, are addressed. Challenges behind anthocyanin implementation in food systems are displayed and potential solutions to overcome these drawbacks are proposed.     

High Endogenously Synthesized N-3 Polyunsaturated Fatty Acids in Fat-1 Mice Attenuate High-Fat Diet-Induced Insulin Resistance by Inhibiting NLRP3 Inflammasome Activation via Akt/GSK-3β/TXNIP Pathway

High-fat (HF) diets and low-grade chronic inflammation contribute to the development of insulin resistance and type 2 diabetes (T2D), whereas n-3 polyunsaturated fatty acids (PUFAs), due to their anti-inflammatory effects, protect against insulin resistance. Interleukin (IL)-1β is implicated in insulin resistance, yet how n-3 PUFAs modulate IL-1β secretion and attenuate HF diet-induced insulin resistance remains elusive. In this study, a HF diet activated NLRP3 inflammasome via inducing reactive oxygen species (ROS) generation and promoted IL-1β production primarily from adipose tissue preadipocytes, but not from adipocytes and induced insulin resistance in wild type (WT) mice. Interestingly, endogenous synthesized n-3 polyunsaturated fatty acids (PUFAs) reversed this process in HF diet-fed fat-1 transgenic mice although the HF diet induced higher weight gain in fat-1 mice, compared with the control diet. Mechanistically, palmitic acid (PA), the main saturated fatty acid in an HF diet inactivated AMPK and led to decreased GSK-3β phosphorylation, at least partially through reducing Akt activity, which ultimately blocked the Nrf2/Trx1 antioxidant pathway and induced TXNIP cytoplasm translocation and NLRP3 inflammasome activation, whereas docosahexaenoic acid (DHA), the most abundant n-3 PUFA in fat-1 adipose tissue, reversed this process via inducing Akt activation. Our GSK-3β shRNA knockdown study further revealed that GSK-3β played a pivot role between the upstream AMPK/Akt pathway and downstream Nrf2/Trx1/TXNIP pathway. Given that NLRP3 inflammasome is implicated in the development of most inflammatory diseases, our results suggest the potential of n-3 PUFAs in the prevention or adjuvant treatment of NLRP3 inflammasome-driven diseases.     

Biosurfactants: Formulations,properties, and applications

In this review, we attempt to give an overview on the recent progress made on biosurfactants, surface-active biomolecules produced by microorganisms, which are a sustainable alternative to synthetic surfactants. Different biosurfactants, their production techniques, and their physical and chemical properties are discussed. There is a focus on recent studies related to surface properties and rheology of biosurfactants, both being properties which affect their ability to take part in a stable formulation. Biosurfactants can have applications in multiple different industrial sectors, such as agriculture, medicine, personal care, food, petroleum, etc. The specific properties important for applications in these sectors are discussed in detail.     

Heterotrophic Cultivation of Euglena gracilis in Stirred Tank Bioreactor: A Promising Bioprocess for Sustainable Paramylon Production

Paramylon is a valuable intracellular product of the microalgae Euglena gracilis, and it can accumulate in Euglena cells according to the cultivation conditions. For the sustainable production of paramylon and appropriate cell growth, different bioreactor processes and industrial byproducts can be considered as substrates. In this study, a complex medium with corn steep solid (CSS) was used, and various bioreactor processes (batch, fed batch, semicontinuous and continuous) were performed in order to maximize paramylon production in the microalgae Euglena gracilis. Compared to the batch, fed batch and repeated batch bioprocesses, during the continuous bioprocess in a stirred tank bioreactor (STR) with a complex medium containing 20 g/L of glucose and 25 g/L of CSS, E. gracilis accumulated a competitive paramylon content (67.0%), and the highest paramylon productivity of 0.189 g/Lh was observed. This demonstrated that the application of a continuous bioprocess, with corn steep solid as an industrial byproduct, can be a successful strategy for efficient and economical paramylon production.     

Plant-Derived Pesticides as an Alternative to Pest Management and Sustainable Agricultural Production: Prospects,Applications and Challenges

Pests and diseases are responsible for most of the losses related to agricultural crops, either in the field or in storage. Moreover, due to indiscriminate use of synthetic pesticides over the years, several issues have come along, such as pest resistance and contamination of important planet sources, such as water, air and soil. Therefore, in order to improve efficiency of crop production and reduce food crisis in a sustainable manner, while preserving consumer’s health, plant-derived pesticides may be a green alternative to synthetic ones. They are cheap, biodegradable, ecofriendly and act by several mechanisms of action in a more specific way, suggesting that they are less of a hazard to humans and the environment. Natural plant products with bioactivity toward insects include several classes of molecules, for example: terpenes, flavonoids, alkaloids, polyphenols, cyanogenic glucosides, quinones, amides, aldehydes, thiophenes, amino acids, saccharides and polyketides (which is not an exhaustive list of insecticidal substances). In general, those compounds have important ecological activities in nature, such as: antifeedant, attractant, nematicide, fungicide, repellent, insecticide, insect growth regulator and allelopathic agents, acting as a promising source for novel pest control agents or biopesticides. However, several factors appear to limit their commercialization. In this critical review, a compilation of plant-derived metabolites, along with their corresponding toxicology and mechanisms of action, will be approached, as well as the different strategies developed in order to meet the required commercial standards through more efficient methods.     

From Fish Waste to Value: An Overview of the Sustainable Recovery of Omega-3 for Food Supplements

The disposal of food waste is a current and pressing issue, urging novel solutions to implement sustainable waste management practices. Fish leftovers and their processing byproducts represent a significant portion of the original fish, and their disposal has a high environmental and economic impact. The utilization of waste as raw materials for the production of different classes of biofuels and high-value chemicals, a concept known as “biorefinery”, is gaining interest in a vision of circular economy and zero waste policies. In this context, an interesting route of valorization is the extraction of omega-3 fatty acids (ω-3 FAs) for nutraceutical application. These fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have received attention over the last decades due to their beneficial effects on human health. Their sustainable production is a key process for matching the increased market demand while reducing the pressure on marine ecosystems and lowering the impact of waste production. The high resale value of the products makes this waste a powerful tool that simultaneously protects the environment and benefits the global economy. This review aims to provide a complete overview of the sustainable exploitation of fish waste to recover ω-3 FAs for food supplement applications, covering composition, storage, and processing of the raw material.     

Environmental control of lipids and fatty acid production in the diatomNavicula saprophila

The unique ability of microalgae to accumulate large amounts of lipids has led to an increase in the research on the cultivation of these organisms for the production of fuels. This paper describes the accumulation of cellular lipids by the diatom,Navicula saprophila, as a result of culture management strategies. The cells were grown in two different nutrient concentrations (nitrogen and silica) maintained at 20° and 30°C. The biomass, lipids, and fatty acids were measured. Biomass yield was higher in a nutrient (nitrogen/silica) nonstress treatment; however, the production of lipids was enhanced in a nutrient stress medium at 30 °C. The influence of the environmental conditions on the distribution of fatty acids was also observed.

     

Valorisation,Green Extraction Development,and Metabolomic Analysis of Wild Artichoke By-Product Using Pressurised Liquid Extraction UPLC–HRMS and Multivariate Data Analysis

Valorisation of food by-products has recently attracted considerable attention due to the opportunities to improve the economic and environmental sustainability of the food production chain. Large quantities of non-edible parts of the artichoke plant (Cynara cardunculus L.) comprising leaves, stems, roots, bracts, and seeds are discarded annually during industrial processing. These by-products contain many phytochemicals such as dietary fibres, phenolic acids, and flavonoids, whereby the most challenging issue concerns about the recovery of high-added value components from these by-products. The aim of this work is to develop a novel valorisation strategy for the sustainable utilisation of artichoke leaves’ waste, combining green pressurised-liquid extraction (PLE), spectrophotometric assays and UPLC–HRMS phytochemical characterization, to obtain bioactive-rich extract with high antioxidant capacity. Multivariate analysis of the major selected metabolites was used to compare different solvent extraction used in PLE.     

Analytical Extraction Methods and Sorbents’ Development for Simultaneous Determination of Organophosphorus Pesticides’ Residues in Food and Water Samples: A Review

Extensive use of organophosphorus pesticides in agriculture leads to adverse effects to the environment and human health. Sample preparation is compulsory to enrich target analytes prior to detection as they often exist at trace levels and this step is critical as it determines the concentration of pollutants present in samples. The selection of a suitable extraction method is of great importance. The analytical performance of the extraction methods is influenced by the selection of sorbents as sorbents play a vital role in the sensitivity and selectivity of an analytical method. To date, numerous sorbent materials have been developed to cater to the needs of selective and sensitive pesticides’ detection. Comprehensive details pertaining to extraction methods, developed sorbents, and analytical performance are provided. This review intended to provide a general overview on different extraction techniques and sorbents that have been developed in the last 10 years for organophosphorus pesticides’ determinations in food and water samples.     

Metabolomic Study of Heterotrophically Grown Chlorella sp. Isolated from Wastewater in Northern Sweden

There are numerous strains of Chlorella with a corresponding variety of metabolic pathways. A strain we previously isolated from wastewater in northern Sweden can grow heterotrophically as well as autotrophically in light and has higher lipid contents under heterotrophic growth conditions. The aims of the present study were to characterize metabolic changes associated with the higher lipid contents in order to enhance our understanding of lipid production in microalgae and potentially identify new compounds with utility in sustainable development. Inter alia, the amino acids glutamine and lysine were 7-fold more abundant under heterotrophic conditions, the key metabolic intermediate alpha-ketoglutarate was more abundant under heterotrophic conditions with glucose, and maltose was more abundant under heterotrophic conditions with glycerol than under autotrophic conditions. The metabolite 3-hydroxy-butyric acid, the direct precursor of the biodegradable plastic PHB (poly-3-hydroxy-butyric acid), was also more abundant under heterotrophic conditions. Our metabolomic analysis has provided new insights into the alga’s lipid production pathways and identified metabolites with potential use in sustainable development, such as the production of renewable, biodegradable plastics, cosmetics, and nutraceuticals, with reduced pollution and improvements in both ecological and human health.     

Crop Yield and Essential Oil Composition of Two Thymus vulgaris Chemotypes along Three Years of Organic Cultivation in a Hilly Area of Central Italy

Thymus vulgaris L. is one of the most commonly used medicinal and aromatic plants (MAPs), owing to a range of therapeutic properties of its essential oil. Plant growth, biomass yield, essential oil content and composition are influenced by chemotype, environmental conditions, cultivation techniques and vegetative development. Since in MAPs cultivation special attention is paid on high quality of raw material, the adoption of sustainable agriculture methods is of pivotal importance. Therefore, we evaluated the agronomic and qualitative performances of two Thymus vulgaris L. chemotypes, organically cultivated under the Mediterranean climate of hilly lands of central Italy for three consecutive years (2017–2019). Along the trial, total above-ground dry biomass significantly increased from the 1st to 3rd year after planting and large variations in the main biological, biometric and productive traits were observed between the two chemotypes. The ‘thymol’ chemotype EO obviously showed thymol as the major constituent (51.26–49.87%) followed by γ-terpinene and p-cymene. The ‘linalool’ chemotype EO showed high percentages of oxygenated monoterpenes (about 90%) with linalool (75%), linalyl acetate (8.15%) and b-caryophyllene (3.2%) as main constituents. This study highlighted that T. vulgaris can be successfully organically grown in the hilly lands of Tuscany, with interesting biomass and essential oil yields, even though the plants were in the initial years of crop establishment (start in 2017). The introduction of this species into organic cultivation systems could contribute to obtain high-quality raw material, as well as to enhance crop rotation diversification, which is of pivotal importance in the management of organic farms.     

Olive Oil Traceability Studies Using Inorganic and Isotopic Signatures: A Review

The olive oil industry is subject to significant fraudulent practices that can lead to serious economic implications and even affect consumer health. Therefore, many analytical strategies have been developed for olive oil’s geographic authentication, including multi-elemental and isotopic analyses. In the first part of this review, the range of multi-elemental concentrations recorded in olive oil from the main olive oil-producing countries is discussed. The compiled data from the literature indicates that the concentrations of elements are in comparable ranges overall. They can be classified into three categories, with (1) Rb and Pb well below 1 µg kg⁻¹; (2) elements such as As, B, Mn, Ni, and Sr ranging on average between 10 and 100 µg kg⁻¹; and (3) elements including Cr, Fe, and Ca ranging between 100 to 10,000 µg kg⁻¹. Various sample preparations, detection techniques, and statistical data treatments were reviewed and discussed. Results obtained through the selected analytical approaches have demonstrated a strong correlation between the multi-elemental composition of the oil and that of the soil in which the plant grew. The review next focused on the limits of olive oil authentication using the multi-elemental composition method. Finally, different methods based on isotopic signatures were compiled and critically assessed. Stable isotopes of light elements have provided acceptable segregation of oils from different origins for years already. More recently, the determination of stable isotopes of strontium has proven to be a reliable tool in determining the geographical origin of food products. The ratio ⁸⁷Sr/⁸⁶Sr is stable over time and directly related to soil geology; it merits further study and is likely to become part of the standard tool kit for olive oil origin determination, along with a combination of different isotopic approaches and multi-elemental composition.