An Integrated Biorefinery Process to Revalorize Marine Biomass from the Microalga Nannochloropsis gaditana Using Pressurized Green Solvents

Abstract

Biorefinery is gaining attention as a promising approach to valorize natural resources and promote a circular bioeconomy. This study aimed to recover high-value molecules, such as xanthophylls and polar lipids with nutraceutical applications, through enzymatic pretreatment and sequential pressurized liquid extraction (PLEseq), by reusing the residual biomass of Nannochloropsis gaditana after each processing step. Remarkably, pure glycolipids (102.95 ± 1.10 mg g^-1 dry weight) were obtained immediately after enzymatic pretreatment, facilitating their easy recovery. Furthermore, two alternative sequential extraction processes were successfully developed, using ethanol and water as green solvents at varying temperatures and in different orders. The most effective PLEseq conditions yielded up to 48 mg mL^-1 of carbohydrates using water at 50 °C, and up to 44 mg mL^-1 of proteins via subcritical water extraction at 100 °C, prior to conventional lipid extraction with ethanol to produce various concentrated extracts. In the inverted PLEseq process-starting with ethanol extraction followed by successive water washes-isolated and purified fractions of lutein and astaxanthin were obtained, contributing to the complete depletion of the residual biomass. Overall, the development of an integrated and sequential biorefinery protocol that enables the extraction of multiple high-value compounds holds significant potential for application in the food industry.

Keywords: Nannochloropsis gaditana; biorefinery; byproducts; carotenoids; microalgae; pressurized liquid extraction (PLE).

Figure 1

Microalgae-based lipid production diagram.

Figure 2

Total protein and carbohydrate content extracted and analyzed in step 1 at different temperatures using water as green solvent (25, 50, and 75 °C).

Figure 3

Total protein and carbohydrate content extracted and analyzed in step 2 at different temperatures (100, 150, and 200 °C) using water as green solvent. In all cases, the first step was developed at 50 °C.

Figure 4

Comparison between total carotenoid content extracted in step 1 and steps 1 + 2. The first extraction was developed using water at different temperatures (25, 50, and 75 °C). Second sequential extraction was developed using water at 100, 150, and 200 °C.

Figure 5

Carotenoid identification and separation of the PLE extracts (from P1.I on the left side to P5.I on the right side) with the inverted process using TLC Silica plates. P1.I corresponded to phase 1 of the inverted process (PLE ethanol), P2.I to phase 2 (PLE water) and P3.I to phase 3 (PLE water). P4.I and P5.I correspond with two additional washes with water.

Figure 6

Schematic representation of the whole process developed where different valuable fractions of N. gaditana were obtained after enzymatic pretreatment. Sequential PLE and inverted sequential PLE are represented.