Subcritical Dimethyl Ether Research Articles

Extraction of neutral lipids and phospholipids from marine biomasses using subcritical and supercritical fluids

Supercritical carbon dioxide (scCO2) and subcritical dimethylether (DME) were used to extract lipids from partially to fully dry marine biomass - whole jack mackerel (WJM), Hoki frames and heads (HFH), and Greenshell mussel meat (GSM). scCO2 gave a lower extraction yield of total lipids from GSM (42%) compared to WFH and HFH (86 - 88% yield) due to the higher concentration of phospholipids present in GSM. DME gave a higher extraction yield of total lipids and phospholipids than scCO2 for all marine biomass types. Phospholipid yield from GSM using DME was dependent on moisture content of the feed marine biomass and decreased with decreasing moisture content. Our results suggested that phospholipid extraction yield can be optimised by partly drying biomass to 30 - 50% moisture prior to extraction. DME extracts contained good levels of omega-3 fatty acids with minimal hydrolytic phospholipid degradation, thus providing a potential processing technology option to recover them from marine biomass.

Separation of Protein from the Meat of Sturgeon by a Subcritical Dimethyl Ether Method

ABSTRACT The feasibility of separating sturgeon protein by subcritical dimethyl ether extraction (SDEE) was investigated, which is an emerging method. In this paper, we found that the protein content of the final product was highest (88.04%) when the SDEE conditions were as follows: 24.93:1 liquid–solid ratio, 51.79 min time, and 862.69 rpm agitation rate. In comparison to pH-shift, the main advantages of SDEE were lower protein loss and higher oil removal. Moreover, the protein obtained by SDEE had superior emulsifying, foaming, and fat absorption properties. In conclusion, the qualities of protein obtained by SDEE are indeed excellent.

Improving the yield and tetracycline adsorption performance of kitchen waste biochar through subcritical dimethyl ether pretreatment

In the context of low-carbon development, it is important to promote resource utilization of kitchen waste, which has the dual properties of pollution and resources. In this study, we explored a method to enhance biochar yield and tetracycline adsorption performance using subcritical dimethyl ether (DME) dewatering and lipid-extraction pretreatment. The mechanism of the effect of lipids and moisture on pyrolysis was investigated by comparing the differences among solid residue biochar, kitchen waste biochar, and dry kitchen waste biochar. Meanwhile, the adsorption performance and mechanism of solid residue biochar on tetracycline was clarified. It was found that lipids did not participate in the generation of biochar, but their decomposition products adhered to the biochar surface. Through DME pretreatment, 95.12% of lipids and 61.34% of moisture could be removed from kitchen waste, the biochar yield was increased by at least 22.77%, and the specific surface area and pore capacity were enhanced. The adsorption performance of tetracycline on solid residue biochar reached 79.11 mg•g−1, and the potential adsorption mechanisms included π-π interaction, hydrogen bonding and pore filling.

Comparison of extraction methods for active biomolecules using sub-critical dimethyl ether and n-butane

Several extraction methods are used to isolate natural compounds, and recent approaches utilize subcritical or supercritical extraction media. In this paper we compare extraction methods based on subcritical eluents, dimethyl ether (sC-DME) and n-butane (sC-nB), under mild conditions, using coffee beans and powder as an exemplary raw material. The parameters to be controlled to improve the extraction are considered, and the resulting data discussed. The results obtained display higher selectivity of sC-DME for caffeine (1.9%w/w sC-DME vs. 1.7%w/w sC-nB, on dry extract) and a good yield (0.479 mg/g of caffeine from green coffee beans) compared to, e.g., supercritical carbon dioxide (SC-CO2), which shows 0.32 mg/g of caffeine at higher pressure and temperature (25 MPa, 40 °C). We also discuss some technical implementations for optimizing the use of sub-critical eluents through proper combinations of pressure and temperature. We show that extraction processes based on sub-critical eluents are easy to operate and efficient, and can be easily automated.

Profiles of sturgeon protein prepared by two methods and the correlation between protein fractions and functional properties

SummaryIn order to find the potential functional components in sturgeon protein, the protein fractions and functional properties of sturgeon proteins (SP) prepared by two methods were investigated, including pH‐shift and subcritical dimethyl ether extraction (SDEE). In the case of the former method, four different experimental conditions were followed. The SP prepared by alkali‐aided pH‐shift had the highest salt‐soluble protein content as well as the lowest water‐soluble protein content, while the highest water‐soluble protein content was observed in SDEE‐produced SP due to a higher proportion of water‐soluble protein that was retained during SDEE. Besides, the significant variations in almost all detected myofibrillar and sarcoplasmic fractions were observed across protein samples, which was mainly due to the solubility of various proteins under different preparation conditions. Moreover, the SDEE‐produced SP possessed the greatest capacities in all the emulsification, foaming and gelation, followed by alkali‐aided pH‐shift and acid‐aided pH‐shift. In addition, the correlation analysis results indicated that enolase, aldolase, PM‐2, TI, NDK, parvalbumin, actin and tropomyosin might be the primary functional components, while PM‐1, CK, MLC3, degradation products and lipids had negative effects on its functional properties. Therefore, changes of the above components might be another important reason to explain how different methods affect the quality of protein, except for the degradation of protein.

Phenanthrene-enriched extract from Eulophia macrobulbon using subcritical dimethyl ether for phosphodiesterase-5A1 inhibition

Eulophia macrobulbon (E.C.Parish & Rchb.f.) Hook.f. contains a natural PDE5A1 inhibitor, phenanthrene, 1-(4'-hydroxybenzyl)-4,8- dimethoxyphenanthrene-2,7-diol (HDP), a potential agent for the treatment of erectile dysfunction. The aim of this study was to improve the extraction efficiency of HDP from E. macrobulbon by using a more environmentally friendly extraction method, subcritical liquid dimethyl ether extraction (sDME), instead of classical solvent extraction (CSE) and ultrasound-assisted extraction (UAE). The efficiency and quality of the extracts obtained were evaluated using the following criteria: %process yield; solvent amount; extraction time; temperature; %HDP content by LC–MS, bioactivity as inhibition of phosphodiesterase-5A1 (PDE5A1) by radio-enzymatic assay; and chemical profiles by LC-QTOF-MS. sDME provided the highest content of HDP in the extract at 4.47%, much higher than the use of ethanol (0.4–0.5%), ethyl acetate (1.2–1.7%), or dichloromethane (0.7–1.4%). The process yield for sDME (1.5–2.7%) was similar to or lower than the other solvents (0.9–17%), but as long as the process yield is not prohibitively low, the concentration is a more important measure for clinical use. The optimal conditions for sDME extraction were: Extraction time, 40 min; 200% water as co-solvent; sample-to-solvent ratio of 1:8; temperature, 35 °C. Phenanthrene aglycone and glycoside derivatives were the major constituents of the sDME extracts and lesser amounts of phenolic compounds and sugars. The inhibition of PDE5A1 by sDME (IC50 0.67 ± 0.22 µg/ml) was tenfold more potent than ethanolic extract and other extraction methods, suggesting a high probability of clinical efficacy. Thus, sDME was a more efficient, faster, solvent-saving and environmentally friendly extraction method and more selective for phenanthrene when extracted from E. macrobulbon.

Physicochemical, digestive and rheological properties of protein from tuna by subcritical dimethyl ether: Focus on process-related indexes

The process-related physicochemical, digestive and rheological properties of protein prepared by subcritical dimethyl ether extraction (SDEE) were comprehensively investigated and compared with those obtained by pH-shift, to study the industrial potential of SDEE. Two different materials from tuna (meat and liver) were studied in parallel, and SDEE had similar effects on the proteins in them.The protein component was almost unchanged before and after SDEE, while the content of water-soluble protein and alkali-soluble protein was substantially reduced and increased after pH-shift, respectively. We also found that SDEE had superior ability to pH-shift to conserve light metals, remove lipids and heavy metals, and maintain protein structure. Furthermore, SDEE-produced protein powders were easier for humans to digest, and their gelation and emulsification were also superior to those prepared by pH-shift. The aforementioned results suggest that SDEE can remove more impurities, and the obtained protein has outstanding potential in industrial applications.

Surfactant-Free Decellularization of Porcine Aortic Tissue by Subcritical Dimethyl Ether.

Porcine aortic tissue was decellularized by subcritical dimethyl ether (DME) used as an alternative to the surfactant sodium dodecyl sulfate. The process included three steps. For the first step, lipids were extracted from the porcine aorta using subcritical DME at 23 °C with a DME pressure of 0.56 MPa. Next, DME was evaporated from the aorta under atmospheric pressure and temperature. The second step involved DNA fragmentation by DNase, which was primarily identical to the common method. For the third step, similar to the common method, DNA fragments were removed by washing with water and ethanol. After 3 days of DNase treatment, the amount of DNA remaining in the porcine aorta was 40 ng/dry-mg, which was lower than the standard value of 50 ng/mg-dry. Hematoxylin and eosin staining showed that most cell nuclei were removed from the aorta. These results demonstrate that subcritical DME eliminates the need to utilize surfactants.

Effect of drying pretreatment methods on structural features and antioxidant activities of Brauns native lignin extracted from Chinese quince fruit

Chinese quince is one kind of crop that has edibility and historical medical applications. However, the high amount of lignin makes processing Chinese quince fruit difficult; on the other hand, this lignin represents a valuable resource if a way of using it in industrial applications could be found. In this study, the structural features and antioxidant activities of Brauns native lignin (BNL) isolated from Chinese quince fruit after oven drying (60 °C, 75 °C, and 90 °C), sun drying, freeze-drying, and subcritical dimethyl ether drying were assessed. The BNL samples had low molecular weights (Mw, 2604–5511 g/mol), high carbohydrate content (6.10–9.95 %), and high phenolic OH content (1.76–2.29 mmol/g). NMR spectra showed that the BNL is of the SGH-type with the relative content of p-hydroxyphenyl units ranging from 13 to 21 %. Oven drying (90 °C) reduced the carbohydrate content and increased the phenolic hydroxyl content. Freeze-drying reduced the relative content of β-O-4′ linkages and increased the H-unit content. In terms of antioxidant activities, all samples possessed high DPPH free radical scavenging capacity (IC50, 0.12−0.22 mg/mL) and strong reducing power. These results indicate that BNL extracted from Chinese quince fruit is a promising source of natural antioxidant and biomass material.

Influence of water content and cell disruption on lipid extraction using subcritical dimethyl ether in wet microalgae

Subcritical dimethyl ether, a green solvent, was used to extract lipids from microalgae. The effect of the water content on the process was firstly investigated. Secondly, microalgal samples were subjected to five cell disruptions, and the effects on raw lipid and fatty acid methyl ester, and its profile were evaluated. Among them, heating, microwave, and ultrasonic treatments greatly improved extraction. Mechanism analysis revealed the improvements by the three treatments were due to increased cell wall permeability rather than to complete cell disruption. After the extraction, microalgal cells with lipid being well-extracted were shriveled with extensive surface folds, indicating a loss of intracellular substances, but the cell structure was undamaged. As for dewatering performance, extraction process removed almost all of the free water but left bound water. Finally, the potential of the residues after lipid extraction to serve as solid fuel was evaluated by combustion characteristics and heating value calculation.

Effective lipid extraction from undewatered microalgae liquid using subcritical dimethyl ether

BackgroundRecent studies of lipid extraction from microalgae have focused primarily on dewatered or dried samples, and the processes are simple with high lipid yield. Yet, the dewatering with drying step is energy intensive, which makes the energy input during the lipid production more than energy output from obtained lipid. Thus, exploring an extraction technique for just a thickened sample without the dewatering, drying and auxiliary operation (such as cell disruption) is very significant. Whereas lipid extraction from the thickened microalgae is complicated by the high water content involved, and traditional solvent, hence, cannot work well. Dimethyl ether (DME), a green solvent, featuring a high affinity for both water and organic compounds with an ability to penetrate the cell walls has the potential to achieve this goal.ResultsThis study investigated an energy-saving method for lipid extraction using DME as the solvent with an entrainer solution (ethanol and acetone) for flocculation-thickened microalgae. Extraction efficiency was evaluated in terms of extraction time, DME dosage, entrainer dosage, and ethanol:acetone ratio. Optimal extraction occurred after 30 min using 4.2 mL DME per 1 mL microalgae, with an entrainer dosage of 8% at 1:2 ethanol:acetone. Raw lipid yields and its lipid component (represented by fatty acid methyl ester) contents were compared against those of common extraction methods (Bligh and Dryer, and Soxhlet). Thermal gravimetry/differential thermal analysis, Fourier-transform infrared spectroscopy, and C/H/N elemental analyses were used to examine differences in lipids extracted using each of the evaluated methods. Considering influence of trace metals on biodiesel utilization, inductively coupled plasma mass spectrometry and inductively coupled plasma atomic emission spectroscopy analyses were used to quantify trace metals in the extracted raw lipids, which revealed relatively high concentrations of Mg, Na, K, and Fe.ConclusionsOur DME-based method recovered 26.4% of total raw lipids and 54.4% of total fatty acid methyl esters at first extraction with remnants being recovered by a 2nd extraction. In additional, the DME-based approach was more economical than other methods, because it enabled simultaneous dewatering with lipid extraction and no cell disruption was required. The trace metals of raw lipids indicated a purification demand in subsequent refining process.

Microalgae preparation and lipid extraction by subcritical dimethyl ether

Biodiesel produced from microalgae is a potential alternative due to the high growth rate of microalgae, the possibility of using nonarable land, and high lipid accumulation rate. Microalgae cultivation, cell harvesting and disruption are the important steps before lipid extraction for the biodiesel. In the co-submission article, the details of the whole process cannot be clearly explained. In this regard, we present the details of methods on parameter of photo-bioreactor for cultivating microalgae, flocculation tests to determine optimal flocculant dosage in harvesting, parameter of Dimethyl ether (DME) subcritical extraction device and full-factorial design for investigating the influence of extraction time, initial water content and DME dosage on the extraction performance. It will allow researchers to reproduce these experiments.• The method shows a cell disruption assisted lipid extraction by subcritical dimethyl ether.• Model is built from full-factorial design to investigate multi-factor influence.• Differential scanning calorimetry can be applicable to measure free water content.

Extraction of Oat Lipids and Phospholipids Using Subcritical Propane and Dimethyl Ether: Experimental Data and Modeling

AbstractEffects of subcritical solvents (propane, dimethyl ether (DME), and their 1:1 mixed solvents) and extraction temperatures (30 to 60 °C) on oat lipids and phospholipid extraction are investigated using the Patricelli kinetic model and thermodynamic analysis. The mass‐transfer coefficient (k1) of the washing stage is approximately ten times higher than the diffusion stage under different solvents and temperature conditions. Compared with the subcritical propane and mixed solvents, the maximum equilibrium yield of oat lipids and phospholipids are obtained using subcritical DME. With increased extraction temperature from 30 to 60 °C, the equilibrium yield of phospholipids increases, whereas the equilibrium yield of lipids increases to 5.30% at 40 °C and then decreases. The enthalpy and entropy changes for phospholipid extraction are higher than those for lipid extraction. The Gibbs free energy for phospholipid extraction rapidly decreases with increased extraction temperature. A loose endosperm of oat grain is observed, and the concentration of lipids in the bran layer is higher than in the endosperm. In conclusion, kinetic and thermodynamic analyses statistically prove that DME is more effective than propane and mixes solvents for extracting lipids and phospholipids from oat flakes, and that phospholipid extraction strongly depends on temperature.Practical Application: The removal of lipids and phospholipids benefits oat‐product processing and storage. However, traditional industrial n‐hexane extraction usually requires a high‐temperature process for solute–solvent separation, which may result in low quality of the meal. Subcritical‐fluid extraction is a rising technology for lipid and phospholipid extraction. The yields of lipids and phospholipids using subcritical dimethyl ether (DME) is higher than those propane and its mixed solvents. The temperature dependence of phospholipid extraction is more active than that of lipid extraction. Thus, use of subcritical DME is a promising lipid‐extraction technique to obtain solvent­free oat oil and high‐quality defatted oat flour with potential application in the oat‐processing industry.

Subcritical dimethyl ether extraction as a simple method to extract nutraceuticals from byproducts from rice bran oil manufacture

The byproducts of rice bran oil processes are a good source of fat-soluble nutraceuticals, including γ-oryzanol, phytosterol, and policosanols. This study aimed to investigate the effects of green technology with low pressure as the subcritical fluid extraction with dimethyl ether (SUBFDME) on the amount of γ-oryzanol, phytosterol, and policosanol extracted from the byproducts and to increase the purity of policosanols. The SUBFDME extraction apparatus was operated under pressures below 1 MPa. Compared to the chemical extraction method, SUBFDME gave the highest content of γ-oryzanol at 924.51 mg/100 g from defatted rice bran, followed by 829.88 mg/100 g from the filter cake, while the highest phytosterol content was 367.54 mg/100 g. Transesterification gave the highest extraction yield of 43.71% with the highest policosanol content (30,787 mg/100 g), and the SUBFDME method increased the policosanol level from transesterified rice bran wax to 84,913.14 mg/100 g. The results indicate that the SUBFDME method is a promising tool to extract γ-oryzanol and phytosterol and a simple and effective technique to increase the purity of policosanol. The study presented a novel technique for the potential use of SUBSFDME as an alternative low-pressure and low-temperature technique to extract γ-oryzanol and phytosterol. The combination of transesterification and the SUBFDME technique is a potential simple two-step method to extract and purify policosanol, which is beneficial for the manufacture of dietary supplements, functional foods and pharmaceutical products.

Rapid preparation of protein powder from high-moisture tuna liver: New insight into subcritical dimethyl ether

The subcritical dimethyl ether extraction (SDEE) was applied in the preparation of liver protein powder (LPD) in this paper. As expected, the lipids and water in tuna liver were co-removed by SDEE, and LPD with a high protein content could be obtained. Besides that, the maximal protein content (88.51%) of LPD was obtained by optimized extraction conditions (liquid-solid ratio 34 mL/g, time 70 min and stirring speed 945 rpm).Furthermore, the traditional preparation technique, pH-shift, was used for comparisons. Compared with pH-shift, the higher quality LPD could by obtain by SDEE with slight fishy and excellent yield, because of SDEE could prevent the loss of nutrition constituents and remove more flavor-active components. Moreover, the functional properties of prepared LPDs were compared with soybean protein powder (SPD) and egg white powder (EWP). The results showed that the LPD prepared by SDEE possessed the greater capacities in foaming, foam stability and fat absorption. Therefore, SDEE, with the advantages of no freeze-drying procedure and relatively low pressure, would be a better alternative to prepare high-quality protein powder in the food industry.

Effect of various drying pretreatments on the structural and functional properties of starch isolated from Chinese yam (Dioscorea opposita Thumb.)

The objective of the present investigation was to compared the structural and functional properties of starch isolated from fresh raw Chinese yam (FYS) and the Chinese yam after freeze-drying pretreatment (FDS), after hot-air drying pretreatment (HADS), after subcritical dimethyl ether dewaterization pretreatment (SDDS). Freeze-drying (FD) process reduced the short-and long-range molecular order of Chinese yam starch. Hot-air drying (HAD) process promoted the formation of ordered structure of starch granules. SEM images displayed the presence of protein-starch complexes in the HADS and SDDS samples. The FDS had the smallest Mw of amylopectin with 4.09 × 106 g/mol, but the Mw values of amylose molecules for FYS was highest. The branch chain length of amylopectin in HADS had a smaller proportion of short chains and less long chains and higher proportion of long chains compared with other starches. These molecular structure changes caused by the various drying pretreatment processes, resulting in the difference in functional properties including solubility and swelling power, gelatinization parameters, pasting characteristics and rheological properties. This study provided important information for the suitable application of starches isolated from various dried Chinese yam.

Effect of drying pretreatment methods on structure and properties of pectins extracted from Chinese quince fruit

Pectin was extracted from the sun-dried, lyophilized, and subcritical dimethyl ether (DME) dewatered fruits as well as fresh fruits, giving rise to fractions SP, LP, DP, and FP, respectively. The structure and properties of the pectin samples were investigated. Among all the pectin samples, LP had the highest yield (10.49%), the highest molar mass (Mw 65,120 g/mol), and the highest water holding capacity, and was the most thermally stable. In addition, LP exhibited the highest DPPH scavenging activity and reducing power. DP had the highest degree of esterification (72.95%), the lowest molar mass (Mw 45,860 g/mol), and the highest oil holding capacity. The four pectin samples had different surface morphology. At the concentration of 2.5% (w/w) in water, all four pectins presented pseudo-plastic behavior. The study provides theoretical support for the potential application of Chinese quince pectin in food field.

Extraction of oil from wet Antarctic krill (Euphausia superba) using a subcritical dimethyl ether method.

In this study, a novel method for obtaining high-quality krill oil from wet Antarctic krill by using subcritical dimethyl ether (SDE) was proposed. A response surface design was used to obtain the best SDE extraction parameters. The optimum extraction efficiency of 93.77 ± 0.92% was obtained at a stirring speed of 1030 rpm, temperature of 47 °C and dynamic extraction time of 90 min. Compared with n-hexane, ethanol, supercritical CO2 and subcritical n-butane extraction, the krill oil extracted by SDE exhibited low peroxide values (1.46 ± 0.26 mmol kg−1), high astaxanthin (218.06 ± 4.74 mg kg−1), phosphatidylcholine (PC) (33.95 ± 0.65%), and phosphatidylethanolamine (PE) (11.67 ± 0.23%) content. Moreover, krill oil extracted by SDE has high levels of EPA (16.38 ± 0.05%) and DHA (7.91 ± 0.07%). SDE extraction proved to be an efficient and safe method for extraction of quality krill oil from wet Antarctic krill, and it could be a promising method for oil extraction in wet food in future.

Extraction of Oil from High‐Moisture Tuna Livers by Subcritical Dimethyl Ether: A Comparison with Different Extraction Methods

Tuna livers, which are currently discarded in the fish industry, are a valuable source of marine oil rich in n‐3 polyunsaturated fatty acids (PUFAs), vitamin A, and vitamin D. In this study, subcritical dimethyl ether extraction (SDEE) is applied in the extraction of oil from high‐moisture tuna livers. Furthermore, other different extraction methods including wet reduction (WR), enzymatic extraction (EE), and supercritical carbon dioxide fluid extraction (SFE‐CO2) are used for comparisons, to assess the effect of different extraction methods on yield, oil quality, flavor (volatile compounds and sensory assessing), vitamin contents, and fatty acids composition. Compared with traditional methods, the high‐quality liver oil can be obtained with excellent yields by SDEE and SFE‐CO2, because they can prevent the oxidation of lipids, and, reduce the damage of PUFAs and vitamins effectively. Furthermore, only minor differences in volatile compounds and vitamins contents are observed between SDEE‐oil and SFE‐CO2‐oil, which is attributed to the differences in solubility to the solvents used. The oil with higher contents of vitamin A and α‐vitamin E can be obtained by SDEE. The main limitations of SFE‐CO2 are energy‐consuming due to high pressure used and the necessary pre‐treatment of freeze‐drying. However, these drawbacks could be overcome in SDEE because the pressure employed in SDEE is quite low (0.8 MPa) and the freeze‐drying is unnecessary. Therefore, SDEE would be a simple, effective, and promising technique to obtain the high quality oil rich in n‐3 PUFAs and vitamins in the fish oil industry.Practical Applications: Subcritical dimethyl ether extraction (SDEE) is a rising technology in oil extraction. It can extract oil from the high‐moisture materials without freeze‐drying under relatively low pressure. As is known, freeze‐drying is a necessary pre‐processing step in ordinary sub‐ and super‐critical fluid extraction. The high quality of oil can be obtained by SDEE, similar with the quality of the oil obtained by supercritical fluid extraction, with dramatically declined operational costs.Subcritical dimethyl ether extraction (SDEE) can extract oil from the high moisture tuna livers without freeze‐drying under relatively low pressure. Furthermore, the quality of SDEE‐oil is similar to the quality of oil obtained by supercritical carbon dioxide extraction, but substantially better than the oil obtained by wet reduction and enzymatic extraction.

Extraction of oil from high-moisture tuna liver by subcritical dimethyl ether: feasibility and optimization by the response surface method.

The purpose of this paper is to explore the possibilities of subcritical dimethyl ether extraction (SDME) of oil from tuna liver with high-moisture content. The results showed that the oil and water were successfully co-extracted from the liver, and could be easily separated by centrifugation. In addition, the response surface method was employed to optimize the process parameters of SDME, including temperature/pressure, time and stirring speed. It was predicted that a temperature/pressure of 42/0.80 °C/MPa, time of 50 min and stirring speed of 925 rpm were the optimum within the experimental ranges, with an oil yield of 17.46 ± 0.23%. Furthermore, supercritical carbon dioxide extraction (SC-CO2) was studied comparatively. Only minor differences were observed between the oils extracted by SDME and SC-CO2, which indicated the high-quality of the SDME-oil. With no freeze-drying procedure and the relatively low pressure used in SDME, SDME could be a promising technique for extraction of marine fish liver oil.