The effect of cell disruption on the extraction of oil and protein from concentrated microalgae slurries

Chlorella sp. as a promising protein source: insight to novel extraction techniques, nutritional and techno-functional attributes of derived proteins

Amidst the mounting environmental crises and ever-increasing global population, the quest for sustainable food production and resource utilization solutions has taken center stage. Microalgae, with Chlorella species at the forefront, present a promising avenue. They serve as a bountiful protein source and can be conveniently grown in waste streams, thereby tackling food security, environmental sustainability, and economic feasibility. This article embarks on a comprehensive journey through recent research on Chlorella by shedding light on its unique characteristics, its market value, cultivation techniques, and harvesting methods. It also delves into traditional and innovative extraction methods, underscoring the hurdles and breakthroughs in achieving high protein yields from the Chlorella biomass. Moreover, exploration of the protein's nutritional properties, bioactive peptides, and techno-functional attributes, enhance its potential for food applications. Further, this review also examines current market trends in consumer acceptance of this alternative protein and discusses strategies for reducing greenhouse gas emissions in their production. By providing invaluable insights into the current status and future prospects of Chlorella protein, it aspires to make a significant contribution to the ongoing dialogue on sustainable food production and resource management.

Cell rupture of Tetradesmus obliquus using high-pressure homogenization at the pilot scale and recovery of pigments and lipids

Microalgae are promising sources of intracellular metabolites such as proteins, polysaccharides, pigments, and lipids. Thus, this study applied high-pressure homogenization (HPH) techniques on a pilot scale to disrupt the cells of Tetradesmus obliquus. The effects of pressure (P; 150, 250, and 350 bar), suspension concentration (Cs; 1.0, 1.5, and 2.0 % w/v), and number of cycles (Nc; 5, 15, and 25) were evaluated in HPH via a Box-Behnken experimental design. Response surface methodology was applied to optimize the recovery rate (dTr) of pigments and lipids. The specific energy consumption (SEC) and color change gradient (ΔE) of the biomass during HPH were also assessed. The optimal HPH conditions for pigment extraction with 1.5 % Cs (w/v) were as follows: P = 312 bar and Nc = 22 for chlorophyll-a (0.83 g/100 g; dTr = 69 %; SEC = 47.50 kJ/g dry matter); P = 345 bar and Nc = 24 for chlorophyll-b (0.63 g/100 g; dTr = 80 %; SEC = 57.30 kJ/g dry matter); P = 345 bar and Nc = 24 for total carotenoids (0.53 g/100 g; dTr = 79 %; SEC = 54.12 kJ/g dry matter); and P = 350 bar and Nc = 25 for β-carotene (299 µg/g; dTr = 58 %; SEC = 62.08 kJ/g dry matter). The optimal HPH conditions for lipid extraction were P = 350 bar and Nc = 23, with a lipid recovery rate of ≥28 %. Cell disruption during HPH caused a change in the color of the biomass (ΔE) due to the release of intracellular biocompounds. Increasing P and Nc led to higher SECs, ΔE gradients, and pigment and lipid contents. Thus, the levels of recovered pigments and lipids can be indicators of cell disruption in T. obliquus.

Stable isotope labeling and functional gene prediction elucidate the carbon metabolism in fermentative bacteria and microalgae coupling system

The application of the fermentative bacteria and microalgae coupling system in the wastewater treatment has been studied, but there remains few knowledge regarding the organic and inorganic carbon metabolism within this system. In this study, the carbon metabolism of microalgae and fermentative bacteria was elucidated by 13C stable isotope labeling and functional gene prediction, respectively. The 13C glucose and 13C NaHCO3 were used as stable isotope tracers to clarify the organic and inorganic carbon metabolism of microalgae, indicating that approximately 71.5 % of the Acetyl-CoA in microalgae was synthesized from organic carbon sources, while 26.8 % was synthesized through the utilization of inorganic carbon sources. Inorganic carbon sources can enhance the activity of photosynthetic system and facilitate the Calvin cycle. Considering the adequate organic carbon sources and insufficient inorganic carbon sources in the fermentative bacteria and microalgae coupling system, NaHCO3 was added to improve carbon utilization of microalgae. The maximum microalgal lipid yield reached 1130.37 mg/L with 1000 mg/L NaHCO3 supplementation. Functional gene prediction was used to analysis the effect of various carbon composition on the bacterial carbon metabolism. Notably, the additional inorganic carbon sources increased the abundance of bacterial functional genes associated with the fermentation and acetic acids synthesis, which was advantageous for VFAs production and further promoted microalgae growth. This study can gain a deeper understanding of microbial metabolic mechanisms during the operation of fermentative bacteria and microalgae system, and improve its sustained operational stability.

Extraction methods of algae oils for the production of third generation biofuels - A review

Microalgae are the main source of third-generation biofuels because they have a lipid content of 20-70%, can be abundantly produced and do not compete in the food market besides other benefits. Biofuel production from microalgae is a promising option to contribute for the resolution of the eminent crisis of fossil energy and environmental pollution specially in the transporting sector. The choice of lipid extraction method is of relevance and associated to the algae morphology (i.e., rigid cells). Therefore, it is essential to develop suitable extraction technologies for economically viable and environment-friendly lipid recovery processes with the aim of achieving a commercial production of biofuels from this biomass. This review presents an exhaustive analysis and discussion of different methods and processes of lipid extraction from microalgae for the subsequent conversion to biodiesel. Physical methods based on the use of supercritical fluids, ultrasound and microwaves were reviewed. Chemical methods using solvents with different polarities, aside from mechanical techniques such as mechanical pressure and enzymatic methods, were also analyzed. The advantages, drawbacks, challenges and future prospects of lipid extraction methods from microalgae have been summarized to provide a wide panorama of this relevant topic for the production of economic and sustainable energy worldwide.

Big Things, Small Packages: An Update on Microalgae as Sustainable Sources of Nutraceutical Peptides for Promoting Cardiovascular Health

In 2017, a review of microalgae protein-derived bioactive peptides relevant in cardiovascular disease (CVD) management was published. Given the rapid evolution of the field, an update is needed to illumininate recent developments and proffer future suggestions. In this review, the scientific literature (2018-2022) is mined for that purpose and the relevant properties of the identified peptides related to CVD are discussed. The challenges and prospects for microalgae peptides are similarly discussed. Since 2018, several publications have independently confirmed the potential to produce microalgae protein-derived nutraceutical peptides. Peptides that reduce hypertension (by inhibiting angiotensin converting enzyme and endothelial nitric oxide synthase), modulate dyslipidemia and have antioxidant and anti-inflammatory properties have been reported, and characterized. Taken together, future research and development investments in nutraceutical peptides from microalgae proteins need to focus on the challenges of large-scale biomass production, improvement in techniques for protein extraction, peptide release and processing, and the need for clinical trials to validate the claimed health benefits as well as formulation of various consumer products with the novel bioactive ingredients.