Microwave-assisted extraction of lipid from Nannochloropsis sp. microalgae using brine solution

Microwave-assisted extraction (MAE) technique is considered a potential method for microalgal lipid extraction, but the usage of harmful and non-polar solvents limit its sustainability. Toward attaining an eco-friendly process, a green solvent, brine (NaCl solution) was proposed as MAE solvent to extract lipids from Nannochloropsis sp. microalgae. The main aim of this study is to maintain a high lipid extraction from Nannochloropsis sp. microalgae via MAE-green solvent technique. The solvent for the MAE, brine solution (NaCl dissolved in water) concentration and the microwave parameters were investigated prior to the optimization study. The extraction kinetic was also studied to verify the extraction mechanism using extraction models including Fick’s Law, First and Second- order Rate Law and Patricelli mathematical model. Finally, the product and by- products from the optimized MAE-brine technique was compared to the conventional extraction methods, namely Soxhlet and Bligh and Dyer (B&D). The MAE-solvent extraction was performed in a modified domestic microwave equipped with a temperature controller. After one at a time investigation of the brine solution concentration and the microwave parameters (solid loading, temperature and time), the highest lipid extracted from each parameter were used for the optimization study via response surface methodology experiment utilizing a Central Composite design (CCD). For the kinetic study, the optimized salt concentration and solid loading values were used at temperatures of 60- 100°C. The Soxhlet technique was performed using hexane as a solvent and B&D method was done using a mixture of chloroform and methanol (1:2; v/v). The results show that 10% (w/v) was the best salt concentration for MAE technique resulted in the highest lipid yield (6.88%) at 10% (w/v) solid loading, 100°C and 5 min. Meanwhile, the optimized MAE-brine parameters at 5% (w/v) solid loading, 100°C and 30 min produced 16.1% of lipid. The kinetic models evaluation for MAE-brine at the different temperatures indicate the success of Patricelli mathematical model at describing microalgae lipid extraction following two phases, namely rapid washing phase and slow diffusion phase. Remarkable agreement between the experimental and predicted lipid yield with the highest R2≥ 0.952 and the lowest Root mean square deviation (≤ 8.666%). The lipid extracted by optimized MAE-brine extraction is three times better than Soxhlet extraction (4.5%) and only 2% less than B&D (18%). The extracted lipids had superior fatty acid profile rich in PUFAs (44.5%) compared to Soxhlet (7.07% PUFAs) and B&D method (26.9% PUFAs). Moreover, MAE-brine is capable of producing outstanding by-products amounts (9.5% protein and 11% carbohydrate) compared to Soxhlet (0.5% protein and 0.26% carbohydrate) and B&D (6% protein and 3.1% carbohydrate). Combining microwave technology with brine solvent contributing to development a fast, efficient and green technique for extraction of microalgal products and by-products.

Text FK 2019 154 - ir.pdf Download (1MB)

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