Supercritical extraction and fractionation of natural matter is one of the early and most studied applications in the field of supercritical fluids In the last 10 years, studies on the extraction of classical compounds like essential and seed oils from various sources: seeds, fruits, leaves, flowers, rhizomes, etc, with or without the addition of a co-solvent have been published Supercritical extraction of antioxidants, pharmaceuticals, colouring matters, and pesticides has also been studied The separation of liquid mixtures and the antisolvent extraction are other processes that can perform very interesting separations Mathematical modelling has also been developed and refined for some of these processes The objective of this review is to critically analyze traditional and new directions in the research on natural matter separation by supercritical fluids extraction and fractionation

Supercritical fluid extraction and fractionation of natural matter

Lignin in straw of herbaceous crops

Along more than a decade, R&D on supercritical fluid extraction (SFE) of vegetable matrices has been increasingly reported in the literature. Aiming at portraying the current state of this field and its evolution in terms of raw materials, products, modes of operation, optimization, modeling techniques, and closeness to industrial application, a large compilation of almost 600 essays from 2000 to 2013 has been deeply analyzed in order to unveil those indicators and their trends. Furthermore, strengths and weaknesses are identified, and some remarks that may drive upcoming research are provided. Globally, more than 300 species are reported in the literature, with prevalence of the extraction of seeds (28% of works) and leaves (17%). The main families of extracted compounds, cosolvents and operating conditions adopted are critically examined, being possible to conclude that researchers investigate many times working regions far from the optimum due to practical limitations or absence of experimental optimization. Current phenomenological, statistical and semi-empirical approaches are reviewed, along with scale-up studies, and economic analysis. In the whole, the most comprehensive picture over SFE of vegetable matrices is provided in this review, highlighting pertinent aspects and opportunities that may further consolidate the convincing route of this technology for the next years.

Supercritical fluid extraction of vegetable matrices: Applications, trends and future perspectives of a convincing green technology

Natural product isolation

http://digital.csic.es/bitstream/10261/12445/3/Use%20of%20compressed%20fluids.pdf

Use of compressed fluids for sample preparation: food applications.

Dibenzo[a,c]cyclooctadiene lignans of the genus Schisandra: importance, isolation and determination.

Oleoresin was extracted from ground black pepper with carbon dioxide at 28 MPa and 24 to 60 °C. The yield and contents of piperine in the extract were determined as a function of extraction time and the solvent amount. The concentration profile of piperine inside the fixed bed of pepper was also measured. The total extract contained piperine and essential oil in the proper ratio to be used directly in food industry. The experimental results showed a strong variation of extract composition during the extraction. They were simulated using the extended Lack's model with mass transfer coefficients in the solvent and solid phase and with grinding efficiency as parameters. The parameters were determined individually for each of the three extract components, representing essential oil, piperine, and other nonpolar substances.

Supercritical carbon dioxide extraction of black pepper

Chlorophylls and carotenoids were extracted from leaves of stinging nettle ( Urtica dioica L.) with supercritical and liquid CO 2 . The solvent modified with ethanol (0–7 wt.%) was applied at the pressures of 200, 250 and 280 bar and the temperatures of 25, 40 and 60 °C. Extracts were analysed by means of HPLC and RP-HPLC methods. The maximum yields of chlorophyll a, chlorophyll b, β-carotene and lutein obtained with CO 2 were 73, 100, 24 and 39 mg/100 g dry matter, respectively. In comparison with the extract obtained using conventional solvents, the maximum yields obtained with CO 2 were similar for carotenoids, higher for chlorophyll b and lower for chlorophyll a. Chlorophyll a partially degraded in the extractor to the more soluble pheophytin a; the extent of carotenoid degradation was much lower than that of chlorophylls. The degradation was substantially reduced by addition of a small amount of antioxidant to the solvent. Extraction rates in dependence on extraction conditions were measured both for individual pigments and for oleoresin. A model describing the extraction of a solute that is present in two forms, free and interacting with matrix, was applied to interpret the experimental extraction curves. A loss of volatile substances from the ground nettle leaves and a decrease in β-carotene content from 24 to 18 mg/100 g dry matter was observed during the period of 155 days between the first and last experimental run.

Near-critical extraction of pigments and oleoresin from stinging nettle leaves

β-Sitosterol (22,23-dihydrostigmasterol) and scopoletin (7-hydroxy-6-methoxycoumarin) were extracted from roots of stinging nettle ( Urtica dioica L.) with supercritical and liquid CO 2 . Extraction rates were measured for both oleoresin and the individual substances in dependence on extraction conditions. The solvent modified with ethanol (0–9.4 wt.%) was applied at the pressures of 100, 200, 250 and 280 bar and the temperatures of 25, 40 and 60 °C. Extracts were analysed by means of HPLC method. The maximum yields of β-sitosterol and scopoletin were 0.63 and 0.058 mg/g dry mass, respectively. In comparison with the extract obtained with diethyl ether, the maximum yields obtained with CO 2 were at least two times higher for both investigated substances. A model describing the extraction of a solute that is present in two forms, free and interacting with matrix, was applied to interpret the experimental extraction curves.

Near-critical extraction of β-sitosterol and scopoletin from stinging nettle roots

Biologically active lignans from caulomas (stems) and leaves of Schisandra chinensis were extracted with supercritical carbon dioxide at the pressures 20–27 MPa, temperatures 40, 50 and 60 °C, and solvent-to-feed ratio 36–43. Six major lignans were determined by means of HPLC: schizandrin, gomisin A, deoxyschizandrin, γ-schizandrin, gomisin N and wuweizisu C. At the optimum conditions 27 MPa and 50 °C, the extraction yield of lignans from caulomas was 1.3% dry weight and their content in the extract was higher than 32 wt.%. At the optimum conditions for CO 2 extraction from S. chinensis leaves, 27 MPa and 60 °C, the yield of lignans was 0.22% d.w. and the yield of ( E )-cinnamic acid was 0.18% d.w. Addition of 2–4% ethanol to CO 2 increased the extraction rate but not the final yield of lignans. The solubility of extracted substances in supercritical CO 2 was estimated from their extraction rates.

Milena Bártlová

Papers

Dibenzo[a,c]cyclooctadiene lignans of the genus Schisandra: importance, isolation and determination.

Supercritical carbon dioxide extraction of black pepper

Near-critical extraction of pigments and oleoresin from stinging nettle leaves

Near-critical extraction of β-sitosterol and scopoletin from stinging nettle roots

Supercritical fluid extraction of lignans and cinnamic acid from Schisandra chinensis