Simultaneous cell disruption and lipid extraction of wet aurantiochytrium sp. KRS101 using a high shear mixer

Application of high shear-assisted liquid biphasic system for protein extraction from Chlorella sp

Microalgae is a sustainable alternative source to traditional proteins. Existing pretreatment methods for protein extraction from microalgae still lack scalability, are uneconomical and inefficient. Herein, high shear mixing (HSM) was applied to disrupt the rigid cell walls and was found to assist in protein release from microalgae. This study integrates HSM in liquid biphasic system with seven parameters being investigated on extraction efficiency (EE) and protein yield (Y). The highest EE and Y obtained are 96.83 ± 0.47 % and 40.98 ± 1.27 %, respectively, using 30% w/v K3PO4 salt, 60 % v/v alcohol, volume ratio of 1:1 and 0.5 % w/v biomass loading under shearing rate of 16,000 rpm for 1 min.

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.

Carotenoid Production from Microalgae: The Portuguese Scenario

Microalgae have an outstanding capacity to efficiently produce value-added compounds. They have been inspiring researchers worldwide to develop a blue biorefinery, supporting the development of the bioeconomy, tackling the environmental crisis, and mitigating the depletion of natural resources. In this review, the characteristics of the carotenoids produced by microalgae are presented and the downstream processes developed to recover and purify them are analyzed, considering their main applications. The ongoing activities and initiatives taking place in Portugal regarding not only research, but also industrialization under the blue biorefinery concept are also discussed. The situation reported here shows that new techniques must be developed to make microalgae production more competitive. Downstream pigment purification technologies must be developed as they may have a considerable impact on the economic viability of the process. Government incentives are needed to encourage a constructive interaction between academics and businesses in order to develop a biorefinery that focuses on high-grade chemicals.

Uncovering the Bioactivity of Aurantiochytrium sp.: a Comparison of Extraction Methodologies

Aurantiochytrium sp. is an emerging alternative source of polyunsaturated fatty acids (PUFAs), docosahexaenoic acid (DHA), and squalene, playing an important role in the phasing out of traditional fish sources for these compounds. Novel lipid extraction techniques with a focus on sustainability and low environmental footprint are being developed for this organism, but the exploration of other added-value compounds within it is still very limited. In this work, a combination of novel green extraction techniques (high hydrostatic pressure extraction (HPE) and supercritical fluid extraction (SFE)) and traditional techniques (organic solvent Soxhlet extraction and hydrodistillation (HD)) was used to obtain lipophilic extracts of Aurantiochytrium sp., which were then screened for antioxidant (DPPH radical reduction capacity and ferric-reducing antioxidant potential (FRAP) assays), lipid oxidation protection, antimicrobial, anti-aging enzyme inhibition (collagenase, elastase and hyaluronidase), and anti-inflammatory (inhibition of NO production) activities. The screening revealed promising extracts in nearly all categories of biological activity tested, with only the enzymatic inhibition being low in all extracts. Powerful lipid oxidation protection and anti-inflammatory activity were observed in most SFE samples. Ethanolic HPEs inhibited both lipid oxidation reactions and microbial growth. The HD extract demonstrated high antioxidant, antimicrobial, and anti-inflammatory activities making, it a major contender for further studies aiming at the valorization of Aurantiochytrium sp. Taken together, this study presents compelling evidence of the bioactive potential of Aurantiochytrium sp. and encourages further exploration of its composition and application.

Advances in Lipid Extraction Methods-A Review

Extraction of lipids from biological tissues is a crucial step in lipid analysis. The selection of appropriate solvent is the most critical factor in the efficient extraction of lipids. A mixture of polar (to disrupt the protein-lipid complexes) and nonpolar (to dissolve the neutral lipids) solvents are precisely selected to extract lipids efficiently. In addition, the disintegration of complex and rigid cell-wall of plants, fungi, and microalgal cells by various mechanical, chemical, and enzymatic treatments facilitate the solvent penetration and extraction of lipids. This review discusses the chloroform/methanol-based classical lipid extraction methods and modern modifications of these methods in terms of using healthy and environmentally safe solvents and rapid single-step extraction. At the same time, some adaptations were made to recover the specific lipids. In addition, the high throughput lipid extraction methodologies used for liquid chromatography-mass spectrometry (LC-MS)-based plant and animal lipidomics were discussed. The advantages and disadvantages of various pretreatments and extraction methods were also illustrated. Moreover, the emerging green solvents-based lipid extraction method, including supercritical CO2 extraction (SCE), is also discussed.

Interplay between interfacial behaviour, cell structure and shear enables biphasic lipid extraction from whole diatom cells (Navicula sp.)

HYPOTHESIS

Bacillariophyceae (i.e., diatoms) are an important class of algae with potential use in the production of proteins and lipids including long-chain ω-3 polyunsaturated fatty acids. Biphasic extraction of microalgae lipids using water-immiscible solvents such as hexane, can avoid the excessive energy required to distil solvents from water, but generally requires energy-intensive rupture of the cells. The unique cell structure and surface chemistry of diatoms compared to other microalgae species might allow biphasic lipid extraction without prior cell rupture.

EXPERIMENTS

The kinetics of biphasic lipid extraction from intact Navicula sp. cells was investigated during low-shear and high-shear mixing, and with prior or simultaneous application of ultrasound (20 kHz at 0.57 W/mL). Dynamic interfacial tension measurements and electron microscopic analysis were used to investigate lipid extraction in relation to interfacial behaviour and cell structure.

RESULTS

High yields (>80%) of intracellular lipids were extracted from intact cells over the course of hours upon low-shear contacting with hexane. The cells associated with and stabilised the hexane-water interface, allowing hexane to infiltrate pores in the frustule component of the cell walls and access the intracellular lipids. It was shown that mucilaginous extracellular polymeric substances (EPS) bound to the cell walls acted as a barrier to solvent penetration into the cells. This EPS could be removed by prior ultrasonication. Biphasic extraction was greatly accelerated by shear applied by rotor-stator mixing or ultrasound. High-shear could remove mucilaginous EPS from the cell surfaces to facilitate direct contact of the cell surface with hexane and produced smaller emulsion droplets with increased surface area. The combination of high-shear in the presence of hexane resulted in the in-situ rupture of the cells, which greatly accelerated lipid extraction and allowed high yields of neutral lipid (>95%) to be recovered from freshly harvested cells within less than 5 min. The study demonstrated the ability of shear to enable simultaneous cell rupture and lipid extraction from a diatom alga based on its cell structure and interfacial behaviour.

In situ solvent recovery by using hydrophobic/oleophilic filter during wet lipid extraction from microalgae

While lipid extraction from wet microalgae has attracted attention as an economical method for microalgal biofuel production, few studies have focused the actual separation of extract phase from the emulsified extraction mixture. Here, a novel approach which utilizes hydrophobic/oleophilic filter was developed for the efficient solvent recovery. The filter was surface-modified by coating a functional polymer via initiated vapor deposition for the selective solvent permeability. While acid-treated Chlorella sorokiniana HS1 and n-hexane was stirred for lipid extraction, tubular filter module was immersed into the mixture for separation. The mixture was kept stirred during the separation to inhibit the buildup of cell debris on the filter by inducing crossflow on the filter. Extract phase was separated directly from the raffinate phase with high separation efficiency (> 98.3%) while maintaining permeation flux. The place-, space- and energy-efficient strategy reported here could be a useful tool for the solvent extraction process.

High-Throughput Biochemical Fingerprinting of Oleaginous Aurantiochytrium sp. Strains by Fourier Transform Infrared Spectroscopy (FT-IR) for Lipid and Carbohydrate Productions

The traditional biochemical methods for analyzing cellular composition of oleaginous microorganisms are time-consuming, polluting, and expensive. In the present study, an FT-IR method was used to analyze the cellular composition of the marine oleaginous protist Aurantiochytrium sp. during various research processes, such as strains screening, medium optimization, and fermentation, and was evaluated as a green, low-cost, high throughput, and accurate method compared with the traditional methods. A total of 109 Aurantiochytrium sp. strains were screened for lipid and carbohydrate production and the best results were found for the strains No. 6 and No. 32. The yields and productivities could reach up to 47.2 g/L and 0.72 g/L/h for lipid, 21.6 g/L and 0.33 g/L/h for docosahexaenoic acid (DHA) in the strain No. 6, and 15.4 g/L and 0.18 g/L/h for carbohydrate in the strain No. 32, under the optimal conditions, respectively. These results confirmed potentials of the two Aurantiochytrium sp. strains for lipid, DHA, and carbohydrate productions at industrial scales. The FT-IR method in this study will facilitate research on the oleaginous Aurantiochytrium sp., and the obtained two strains for lipid and carbohydrate productions will provide the foundations for their applications in medical, food, and feed industries.

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.

An Overview of Current Pretreatment Methods Used to Improve Lipid Extraction from Oleaginous Micro-Organisms

Microbial oils, obtained from oleaginous microorganisms are an emerging source of commercially valuable chemicals ranging from pharmaceuticals to the petroleum industry. In petroleum biorefineries, the microbial biomass has become a sustainable source of renewable biofuels. Biodiesel is mainly produced from oils obtained from oleaginous microorganisms involving various upstream and downstream processes, such as cultivation, harvesting, lipid extraction, and transesterification. Among them, lipid extraction is a crucial step for the process and it represents an important bottleneck for the commercial scale production of biodiesel. Lipids are synthesized in the cellular compartment of oleaginous microorganisms in the form of lipid droplets, so it is necessary to disrupt the cells prior to lipid extraction in order to improve the extraction yields. Various mechanical, chemical and physicochemical pretreatment methods are employed to disintegrate the cellular membrane of oleaginous microorganisms. The objective of the present review article is to evaluate the various pretreatment methods for efficient lipid extraction from the oleaginous cellular biomass available to date, as well as to discuss their advantages and disadvantages, including their effect on the lipid yield. The discussed mechanical pretreatment methods are oil expeller, bead milling, ultrasonication, microwave, high-speed and high-pressure homogenizer, laser, autoclaving, pulsed electric field, and non-mechanical methods, such as enzymatic treatment, including various emerging cell disruption techniques.