Joana Oliveira

Global population growth has emphasised the need to have sustainable and alternative sources of nutrients. In this context, microalgae have emerged as a potential solution due to their rich biochemical composition, including high-quality proteins, carbohydrates, lipids, and pigments. This study investigates the variation in microalgal growth and biochemical composition over a light:dark cycle, with a focus on the night period. Batch experiments were performed with eight Chlorella vulgaris cultures over a 7-day period. On the seventh day, biomass samples were collected at four time points in four-hour intervals and stored for subsequent biochemical analyses. During the eight-hour dark period, biomass, carbohydrate, and total chlorophyll concentrations decreased by 9%, 12.5%, and 14.4%, respectively. After four hours of light exposure, these parameters increased significantly by 6%, 15.4%, and 12.7%, respectively. Total protein, carotenoids, and fatty acid contents remained relatively stable throughout the evaluated cycle, although variations were observed in the carotenoid profile. During the dark phase, zeaxanthin decreased by 38.0%, whereas violaxanthin increased by 27.2%, suggesting complementary pigment interconversion consistent with xanthophyll cycle activity. Overall, these results highlight the importance of optimising harvesting time to enhance the production of target compounds in a sustainable production of microalgal biomass.

Microalgae are photosynthetic microorganisms with high biotechnological potential, though optimising inorganic carbon supply remains a critical challenge to enhance growth, biomass quality, and carbon use efficiency. To address this, this study evaluated the impact of sodium bicarbonate supplementation (0, 0.5, 1.5, and 3.0 g L⁻¹) on Chlorella vulgaris growth, carbon dynamics, biochemical composition, and metabolism over 11 days. Higher carbon availability (3.0 g L⁻¹ NaHCO₃) increased the specific growth rate to 0.472 ± 0.004 d⁻¹, accelerated nitrogen removal (85% by day 4), enhanced phosphorus removal (up to 90% by the end of cultivation), and increased dissolved inorganic carbon uptake (93 ± 6 mg L⁻¹). Carbohydrate and lipid contents were not significantly affected by bicarbonate concentration, whereas protein and pigment levels were higher in non-supplemented conditions due to prolonged exponential growth. Bicarbonate supplementation enhanced MUFA content, improving biodiesel quality. Amino acid profiles were similar across conditions, with glutamic acid as the predominant amino acid (up to 17 mg g⁻¹ DW) and higher values under moderate bicarbonate supplementation (1.5 g L⁻¹). Overall, bicarbonate supplementation enhanced microalgal growth, nutrient removal efficiency, and fatty acid composition, highlighting its potential to improve carbon availability for C. vulgaris cultivation.

Interest in microalgae-based technologies has emerged in recent years as a response to environmental challenges and the global food crisis, for providing alternative and sustainable food products. This study used temperature variations between 18 and 32 °C and nitrogen-to-phosphorus (N:P) ratios between 1.9 and 42.6 to model and optimize growth and composition of Chlorella vulgaris, a nutritionally interesting species. Lower temperatures appear ideal for this strain. An increase in average biomass productivity was observed with decreasing temperature, leading to a maximum of 122.27 mg_dw L⁻¹ d⁻¹ at 18 °C on the fourth day of cultivation. The maximum productivities for total proteins, fatty acids, carbohydrates, and pigments were, respectively, 26.9 mg L⁻¹ d⁻¹, 26.4 mg L⁻¹ d⁻¹, 16.0 mg L⁻¹ d⁻¹, and 2.41 mg L⁻¹ d⁻¹, all referring to 18 °C. The fatty acid, carotenoid, and amino acid profiles were also ascertained; several indicators suggested that cultivation of these microalgae under the aforementioned optimal conditions holds potential for the food industry. The high proportion of polyunsaturated fatty acids—including two essential fatty acids; the high production of lutein, and the presence of several essential amino acids are among the favorable indicators. Overall, the information generated by this study is helpful to support future pilot studies aimed at the commercial production of microalgae-derived products.

Interest in microalga-based technologies has emerged in recent years as a response to environmental challenges and the global food crisis for providing alternative and sustainable food products. This study used temperature variations between 18 and 32 °C, and nitrogen-to-phosphorus (N:P) ratios between 1.9 and 42.6, to model and optimize growth and composition of Chlorella vulgaris, a nutritionally interesting species. Lower temperatures appear ideal for this strain. An increase in average biomass productivity was observed with decreasing temperature, leading to a maximum of 122.27 mg_dw L^-1 d^-1 at 18 °C on the 4^th day of cultivation. The maximum productivities for total proteins, fatty acids, carbohydrates, and pigments were, respectively, 26.9 mg L^-1 d^-1, 26.4 mg L^-1 d^-1, 16.0 mg L^-1 d^-1, and 2.41 mg L^-1 d^-1, all referring to 18 °C. The fatty acid, carotenoid, and amino acid profiles were also ascertained; several indicators suggested that cultivation of this microalga under the aforementioned optimal conditions holds potential for the food industry. The high proportion of polyunsaturated fatty acids, including two essential fatty acids; the high production of lutein; and the presence of several essential amino acids are among the favorable indicators. Overall, the information generated by this study is helpful to support future pilot studies aimed at the commercial production of microalga-derived products.

Microalgae are lipid-rich microscopic eukaryotic algae that can be used aiming for more sustainable biodiesel production by employing environmentally sound processes. The present work evaluates biodiesel production using a biocatalyst and two microalgae species as oil feedstock (Chlorella vulgaris and Aurantiochytrium sp.). Lipid extraction was performed using different techniques, namely, Soxhlet extractions (8 h — both species) with different solvents (hexane; hexane:ethanol (1:1 v/v); and chloroform) and room temperature hexane extraction (72 h — Aurantiochytrium sp.). Transesterification occurred for 24 h (150 rpm), using 30 % lipase loading. The results showed that high extraction temperatures cause microalgae oil degradation, focused on unsaturated fatty acids, leading to a lower biodiesel conversion yield. Using Aurantiochytrium sp. oil, it was possible to obtain around 55 %wt. of biodiesel conversion yield using oil extracted at room temperature (6:1 methanol:oil molar ratio), whereas for the oil extracted in the Soxhlet apparatus, the biodiesel conversion yield was around 30 %wt.. The low lipid content (1.0 %wt.) and biodiesel conversion yield (up to 25 %wt.) obtained using C. vulgaris show that the biomass used in the current study has low potential for biodiesel production. However, enzymatic biodiesel production from microalgae represents a promising avenue for sustainable energy generation, offering a renewable and environmentally responsible solution to the world’s energy needs. For that purpose, further studies, such as the optimisation of the extraction and transesterification of Aurantiochytrium sp. oil, should be carried out.

Microalgae are a promising feedstock for bioethanol production, essentially due to their high growth rates and absence of lignin. Hydrolysis—where the monosaccharides are released for further fermentation—is considered a critical step, and its optimization is advised for each raw material. The present study focuses on the thermal acid hydrolysis (with sulfuric acid) of Aurantiochytrium sp. through a response surface methodology (RSM), studying the effect of acid concentration, hydrolysis time and biomass/acid ratio on both sugar concentration of the hydrolysate and biomass conversion yield. Preliminary studies allowed to establish the range of the variables to be optimized. The obtained models predicted a maximum sugar concentration (18.05 g/L; R² = 0.990) after 90 min of hydrolysis, using 15% (w/v) biomass/acid ratio and sulfuric acid at 3.5% (v/v), whereas the maximum conversion yield (12.86 g/100 g; R² = 0.876) was obtained using 9.3% (w/v) biomass/acid ratio, maintaining the other parameters. Model outputs indicate that the biomass/acid ratio and time are the most influential parameters on the sugar concentration and yield models, respectively. The study allowed to obtain a predictive model that is very well adjusted to the experimental data to find the best saccharification conditions for the Aurantiochytrium sp. microalgae.