Recovery of aqueous phase of sub-critical water extraction (SWE) from Nannochloropsis gaditana

Microalgae had been proven to be rich in valuable biochemical components such as antioxidants and omega-3. Sub-critical water extraction (SWE) is considered an excellent technology for extraction as the process involves shorter extraction period with high efficiency and it uses a green solvent which is only water. Additional benefit of SWE would be the potential to recover the aqueous extracts which is rich in compounds such as sugar and organic carbon. Sugar could be used in fermentation process for bioenergy production and total organic carbon (TOC) could be used for nutrient recycling for microalgal cultivation. In this experiment, the process conditions of SWE include temperature (156°C-274°C), biomass loading (33 g/L-117 g/L) and retention time (6.6 min-23.4 min) were investigated to quantitatively determined the yield of the aqueous products, focusing on sugars and TOC. The experiments were designed using Central Composite Design (CCD) and the statistical analysis was performed using Design-Expert 7.0. The responses and interactions of each parameter towards the content of the aqueous phase were discussed. A second order polynomial model was chosen for both carbohydrates and TOC content with R2 = 0.9835 and R2 = 0.9845 respectively. The statistical tool also generates predictive equations which could be used to predict future experiments

Extraction of bioactive compounds from Nannochloropsis gaditana via sub-critical water extraction (SWE)

Microalgae are being consumed as supplements because they are rich in protein, vitamins, carbohydrates and lipids. Hence, extraction processes to obtain the bioactive compounds are being extensively studied and developed. Sub-critical water extraction (SWE) technology has been used in extracting active compounds from different biomass materials with low process cost, mild operating conditions, short process times, and environmental sustainability. Therefore, this study utilizes SWE for extracting biochemical compounds such as lipids, carbohydrates and protein from Nannochloropsis gaditana. Different parameters were applied include temperature (156°C-274°C), biomass loading (33 g/L-117 g/L) and retention time (6.6 min-23.4 min) for maximum production of those compounds. It was found that higher crude oil yield of 17.86 wt% was achieved under SWE (215oC, 15 min, 75 g/L) compared to conventional method (10.2 wt%). The similar pattern was also observed for carbohydrates and protein yields as shown by Fourier transform infrared spectroscopy (FT-IR) result. Overall, the findings of this study will benefit food and pharmaceutical industries as well as enhancing the usage of this abundant biomass for commercial purposes

Optimization of sub-critical water extraction (SWE) of lipid and eicosapentaenoic acid (EPA) from Nannochloropsis gaditana

Microalgae are a promising source of omega-3. The purpose of this study was to extract lipid with a relatively high content of eicosapentaenoic acid (EPA) from Nannochloropsis gaditana using subcritical water extraction (SWE). The effects of different temperatures (156.1-273.9°C), extraction times (6.6-23.4 minutes), and biomass loadings (33-117 g algae/L) on the extraction yield were studied. From the optimization study using central composite design (CCD), quadratic models generated for lipid yield and EPA composition were considered to be significant models (p < 0.05). The predictive equations were also formed for lipid yield and EPA composition. The predicted optimum lipid yield and EPA composition at 236.54°C, 13.95 minutes, and 60.50 g algae/L were 18.278 wt% of total biomass and 14.036 wt% of total fatty acid methyl ester (FAME), respectively

Kinetic and thermodynamic characterization of amino acids generation via subcritical water reaction of microalgae Nannochloropsis sp. biomass

Emerging applications of amino acids in the development of biopharmaceuticals, functional foods and feeds, and biostimulants in sustainable agriculture have led to increasing interests in the development of commercially-viable technologies for amino acid production. Amongst the many technologies currently used, subcritical water reaction has the potential to offer a scalable and environmentally benign approach to amino acids synthesis. The present work investigates the kinetic and thermodynamic behaviour of amino acids synthesis from Nannochloropsis sp. biomass using subcritical water. Experiments were conducted in a batch reactor at temperatures between 250-280°C for a duration of 5-20 min using 1% (w/v) microalgal loading. The aqueous phase obtained from the reaction was directly analyzed for amino acid concentration. The highest amino acids yield of 0.0196 g AA / g biomass was obtained at 260°C for 20 min, representing 44% of amino acids extracted from the biomass. A single consecutive reaction model used for data validation showed a good agreement between the experimental and theoretical data generated. The results obtained from the kinetic study demonstrated that amino acids could be produced and decomposed rapidly from the subcritical water process. Thermodynamic analysis by transition-state theory showed that the subcritical water process as endothermic, while the Gibbs free energy showed the reaction as non-spontaneous, requiring constant external energy to support it

Subcritical water extraction of lipid containing omega-3 from microalgae Nannochloropsis gaditana

Omega-3 fatty acids, mainly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are known to have many health benefits. Many researchers have found different algal species which have high omega-3 content. Conventional techniques such as to extract microalgal omega-3 have too many disadvantages. This hinders the application of the extracted products to be fully utilized for human consumption. Therefore, a need for green, fast, and robust approach to extract the lipids from microalgae is essential. This study investigates the effectiveness of subcritical water extraction (SWE) in extracting lipid and EPA from microalgae, Nannochloropsis gaditana. The preliminary screening of SWE experiments were carried out to identify the suitable range of parameters. The highest yield of lipid for the preliminary screening was at a temperature of 210℃ and reaction time of 10 min yielding 20.79 wt% of lipid. After screening, an optimization is done with the parameters set on extraction temperature (156.1-273.9℃), time (6.6-23.4 minutes), and biomass loading (33-117 g algae/L) that are further optimized for lipid yield and EPA composition using central composite design (CCD). All three parameters were found to be significant factors for the changes in lipid yield, but extraction time was not a significant factor for EPA composition change. It was found that the predicted optimum lipid yield and EPA composition at 236.54 ℃, 13.95 minutes and 60.50 g algae/L was 18.278 wt% of total biomass and 14.036 wt% of total fatty acid methyl ester (FAME), respectively. Furthermore, the separation of the lipid extracts was performed using a solid phase extraction (SPE) method, where the lipids were classified into polar lipid (POL), neutral lipid (NL) and free fatty acid (FFA) component. From the findings, the POL was more susceptible to hydrolysis than NL. The highest recoveries of NL and POL from the biomass were 81.16 wt% and 66.45 wt% of lipid as compared to B&D method, respectively. A reaction pathway for SWE of Nannochloropsis gaditana was also developed and used to derive the kinetic equation. The highest rate constant and lowest activation energy was the pathway of algal EPA-POL to be converted into byproducts showing further that EPA-POL have high rate of hydrolysis at higher temperature with activation energy of 37.56 kJ/mol. It was also found that the model successfully incorporated to both major and minor fatty acids present in the microalgae such as palmitoleic acid, linolenic acid, and arachidonic acid. Overall, the outcome of this study contributes to a better utilization of microalgae as an available source of omega-3 fatty acids for food and pharmaceutical industry as well as achieving the green and fast extractions with high concentration of omega-3