Although astaxanthin has promising physiological functions, its practical applications are limited by poor stability. Herein, astaxanthin was encapsulated in β-cyclodextrin (βCD) using CO2 as a ...supercritical antisolvent (SAS). The effects of process conditions, including temperature (313–333 K), pressure (12–18 MPa), solution concentration (3–5 wt%), solution flow rate (0.8–1.2 mL min−1), and astaxanthin-to-βCD mole ratio (1:50, 1:25, or 1:10), on the encapsulation efficiency, particle morphology, and residual solvent content were investigated. Astaxanthin–βCD complex spheres with an average diameter of 0.44 ± 0.08 µm were produced at 313 K and 15 MPa with a solution concentration and flow rate of 5 wt%, and 1.0 mL min−1, respectively. Under these optimal conditions, almost complete encapsulation (99.6% encapsulation efficiency) and residual organic solvent removal (0.22 ppm in the complex) were achieved. Density functional theory analysis of the configuration of the astaxanthin–βCD complex indicate that the hydroxyl hydrogen atoms on an ionone ring of astaxanthin interact with the oxygen atoms of βCD, but the ionone ring does not fit deeply within the βCD cavity. Notably, the astaxanthin–βCD complex exhibits higher thermal stability and antioxidant activity than free astaxanthin. The findings suggest that βCD encapsulation via the SAS process can produce astaxanthin microparticles with potential utility for food and pharmaceutical applications.
•Astaxanthin encapsulation in β-cyclodextrin was achieved using scCO2 as antisolvent.•Supercritical antisolvent (SAS) process produced amorphous microparticles.•Encapsulation efficiency of 99.6% with very low residual DMSO content was achieved.•Encapsulated particles exhibited enhanced thermal stability and antioxidant activity.•Inclusion complex was validated in the molecular level.
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•Green processes involving l-DME and DMSO were developed for microalgal biorefinery.•Drying and cell-wall-disruption steps of wet H. pluvialis were not employed.•Complete recovery of ...astaxanthin and fatty acids from the wet cysts was achieved.•The dry extract exhibited strong antioxidative activities.
Efficient and eco-friendly methods for extracting bioactive molecules are crucial for achieving economically viable microalgae biorefinery. In this study, high-value-added intracellular bioactive compounds were efficiently recovered directly from the red cysts of wet Haematococcus pluvialis. An integrated processes involving liquid dimethyl ether (l-DME) extraction at 45 °C and 2 MPa for 90 min and subsequent dimethyl sulfoxide (DMSO) extraction at 65 °C for 5 min enabled almost complete recovery of astaxanthin (99.6%) and total fatty acids (99.8%) from wet H. pluvialis cyst cells. Notably, this green and sustainable strategy did not involve high-cost and energy-intensive drying, or cell wall-disruption steps. l-DME extraction produced a solvent-free, dry extract with high astaxanthin (43.9 mg g−1 dry extract) and essential fatty acids (ω3, ω6, and ω9; 290.1 mg g−1 dry extract) contents; whereas the astaxanthin and fatty acid contents of the DMSO extract produced from raw H. pluvialis cyst cells (freeze-dried and ball-milled at 200 rpm for 30 min) were 1.5- and 1.7-fold lower, respectively. The dry extract also exhibited 1.6-fold greater antioxidant activity than the DMSO extract, thereby indicating its potential for direct application in nutraceutical, pharmaceutical, and cosmeceutical formulations with high bioactivity and safety.
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•Extraction of rare ginsenosides and bioactive compounds was enhanced by CO2.•CO2 facilitated hydrolysis of red ginseng marc components.•Sugars, rare ginsenoside, and phenolics were ...major extracted species.•CO2-subH2O exhibited 3.5 times higher antioxidant activity than conventional methods.•Reaction pathways for the production of rare ginsenosides were proposed.
Subcritical water extraction (SWE) is a high-efficiency and environmentally sustainable technique for extracting bioactive compounds from red ginseng marc (RGM). In this study, CO2 was introduced into the SWE system as a green catalyst to enhance the extraction efficiency of biologically active compounds from RGM. A wide range of parameters, such as temperature (140–180 °C), pressure (10–20 MPa), and time (10–60 min), were optimized using response surface methodology to maximize the recovery of highly valuable bioactive components, including rare ginsenosides (RGs), total phenolic contents (TPCs), and Maillard reaction products (MRPs), as well as the antioxidant activity of the RGM extract. The extract obtained using CO2-assisted SWE (CO2-SWE) under the optimal conditions (172 °C, 10 MPa, and 10 min) was enriched in RGs (1.02–2.16 times), TPCs (0.98–4.68 times), and MRPs (1.08–2.20 times) and exhibited enhanced antioxidant activities (1.07–3.50 times) compared with the extracts produced by conventional SWE (N2 environment) and Soxhlet extraction with H2O or 80 vol% ethanol. Thus, CO2-SWE is an environmentally friendly and nontoxic technique with considerable potential for use in the pharmaceutical, cosmeceutical, and functional food sectors.
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•Astaxanthin was directly recovered from wet encyst H. pluvialis in a one-pot system.•Extraction yield of 58.2 wt% and astaxanthin recovery of 30.6 mg/g were achieved.•Biphasic ...solvent system plays a key role in achieving high extraction yields.•The extraction was performed at mild condition (200 rpm, 30 min, <25 °C).•The extract exhibited high antiradical activities.
A novel integrated extraction technique for high recovery of natural astaxanthin from wet encysted Haematococcus pluvialis (H. pluvialis) is demonstrated. The technique can be used to effectively disrupt the cell wall and perform extraction in a one-pot system without a high-energy, cost intensive pre-drying step. The most suitable green solvent was researched in terms of high extraction yield and astaxanthin recovery. Moreover, an optimized condition for the selected green solvents was determined by varying process parameters, viz., the ball milling speed (100–300 rpm) and time (5–30 min). A high recovery of astaxanthin directly from wet H. pluvialis (30.6 mg/g based on its dry mass) and a high extraction yield (58.2 wt%) were achieved using ethyl acetate at 200 rpm after 30 min. Therefore, compared to its counterparts, the biphasic solvent system plays a key role in achieving high extraction yield and astaxanthin recovery from wet H. pluvialis.
•The co-use of supercritical CO2 and carbon results in the significant synergy in cellulose hydrolysis.•Supercritical CO2 and water form a Pickering emulsion, enhancing the cellulose-carbon ...contact.•The initial cellulose hydrolysis rate increases up to 3 × at the emulsion interface.•The in-situ formed carbonic acid (pH ∼ 3.1) helps to hydrolyze oligosaccharides to glucose.•The promoting role of supercritical CO2 in cellulose hydrolysis is more profound in the mix-milled cellulose.
Rapid depolymerization of cellulose into processable monomers (e.g., sugars) using solid acid catalysts is an important step for cost-effective biofuel and biochemical production, but has not yet been achieved due to the limited contact between solid cellulose and solid catalysts. Herein, the unique roles of supercritical CO2 (i.e., scCO2) as an in-situ acid catalyst and reaction solvent in achieving the ultra-fast full solid catalytic hydrolysis of cellulose are disclosed for the first time. When the ball-milling pretreated cellulose was hydrolyzed using oxidized carbon catalysts at 150 °C and 100–300 bar-CO2, the hydrolysis kinetics remarkably increased by 3× for conversion and 5× for glucose, resulting in ∼90% conversion and ∼85% total sugar selectivity at 20 min. The hydrolysis rate obtained with scCO2 here was higher than conventional ones with toxic and unrecyclable homogeneous catalysts (e.g., HCl) under harsh reaction conditions (i.e., 180–220 °C and pH of 1–2). A comprehensive reaction engineering study (e.g., temperature, CO2 pressure, stirring speed, catalyst acid properties) combined with the estimation of the solution pH by the CO2 phase equilibrium model and the in-situ and ex-situ monitoring of the phase behavior of the H2O/scCO2 solution were conducted to quantify the activity promotion by scCO2 and understand the acid-solvent roles of scCO2 toward the enhanced hydrolysis of cellulose. Specifically, the formation of the Pickering emulsions at the interface between scCO2 and water and their impact on the enhancement of the cellulose-carbon contact were proposed and verified in detail.
