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Application of CO2 expanded liquids as green solvents for the extraction of antioxidants

Coto Acosta, Mar LU (2016) KEMP36 20161
Department of Chemistry
Abstract
Antioxidants are compounds present in plant, fruit, and vegetables, and they are known for their medicinal benefits such as anti-carcinogenic and anti-fungicidal activity. Most commonly used methods for extractions of such compounds are lengthy due to mass transfer limitations. This study proposes the use of carbon-dioxide expanded liquids (CXLs) as solvent to improve these limitations. Such solvents, considered as green solvents because of its inertness, odourless and low toxic properties, present tunable physical properties, such as low viscosity and high diffusivity rates. The solubility of CO2 in ethanol determines the volume expansion and, depends on temperature and pressure. Hence, the acquisition of solubility data of analyte in... (More)
Antioxidants are compounds present in plant, fruit, and vegetables, and they are known for their medicinal benefits such as anti-carcinogenic and anti-fungicidal activity. Most commonly used methods for extractions of such compounds are lengthy due to mass transfer limitations. This study proposes the use of carbon-dioxide expanded liquids (CXLs) as solvent to improve these limitations. Such solvents, considered as green solvents because of its inertness, odourless and low toxic properties, present tunable physical properties, such as low viscosity and high diffusivity rates. The solubility of CO2 in ethanol determines the volume expansion and, depends on temperature and pressure. Hence, the acquisition of solubility data of analyte in CXLs and the density of such mixtures will be valuable for an optimum extraction of antioxidant from complex solid samples. Aiming to study these properties, a system able to perform measurement of solubility and phase equilibria was developed. The equipment consists of a high pressure view cell connected in-line to a densitometer and a supercritical fluid chromatograph with a photodiode array detector. Validation of such equipment was performed with curcumin, a polyphenol extracted from Turmeric (Curcuma longa L.), 200 bar and 40 ºC in 92 % CO2 and 8 % ethanol, giving a solubility of 0.37 x 102 (molar fraction) , while in literature the observed value is 0.41 x 102 (molar fraction). Solubility measurements were successfully determined for curcumin at 200 bar, 35 ºC and at different content of ethanol in the mixture– from 50 to 90 %. Densities for such mixtures were also studied. Results have shown that the solubility of curcumin increases with the amount of ethanol as expected. Another polyphenol studies is quercetin, which it was found to be higher in solubility than curcumin. In general terms, the developed equipment has shown to be efficient for the established purpose. Further investigations are needed to confirm the range of applicability. (Less)
Popular Abstract
How chemical properties can improve the extraction of antioxidants?
Analytical chemistry is based on the study of the identification, extraction and separation of compounds of interest, so that the structure and composition of these compounds in a sample are obtained. Different types of samples are of interest for these studies. For instance, the healthy properties attributed to fruits and vegetables (i.e. antioxidant capacity) relies on the analytical determination of its composition. Nevertheless, no possible determination could be done if the compound of interest was not previously extracted from the matrix. An extraction process involves the isolation of a substance – referred as analyte – from a sample by using solvents, which have... (More)
How chemical properties can improve the extraction of antioxidants?
Analytical chemistry is based on the study of the identification, extraction and separation of compounds of interest, so that the structure and composition of these compounds in a sample are obtained. Different types of samples are of interest for these studies. For instance, the healthy properties attributed to fruits and vegetables (i.e. antioxidant capacity) relies on the analytical determination of its composition. Nevertheless, no possible determination could be done if the compound of interest was not previously extracted from the matrix. An extraction process involves the isolation of a substance – referred as analyte – from a sample by using solvents, which have the ability to dissolve the referred substances. For example, coffee beans are the seeds of the coffee plant and they are subjected to extraction processes so we can have our daily cup of coffee. However, extractions are usually lengthy in time, and also costly, due to the amounts of energy and solvent used for it. Moreover, the chemical properties of an analyte (i.e. polarity dependence) make extractions even more challenging, meaning that many parameters must be controlled. Polyphenols are a type of antioxidants which are difficult to extract due to its polarity. Thus, a suitable solvent has to be selected for the extraction.
In this thesis, an interesting and green technique for such processes is presented. This technique uses a so-called carbon dioxide–expanded liquids (CXLs) as extraction solvent. CXLs is a fluid state of carbon dioxide (CO2) above its critical pressure (74 bar) and critical temperature (31 ºC) to which a traditional organic liquid – ethanol in a range content of 50 to 90 % – is added to enhance its properties, like polarity. Therefore, CXL presents tunable physical properties. Consequently, it can be used for extracting polyphenols or any other medium-polar antioxidant compound. Prior to its application in extraction, the study of solvent – analyte interactions is needed. So, this information will be valuable to obtain higher extraction yields.
Solubility plays a major role in the study of an extraction process. A simple example present in our daily basis can be used to exemplify the effect of temperature in extraction. If sugar dissolves better in water at higher temperatures, it is because is a favour temperature process. The same principle applies for extractions. Information of the solubility of analytes in CXLs will lead to extraction improvements. In this thesis, a home-made equipment was developed to acquire solubility measurements. The applicability of such system was tested with solubility measurements of curcumin, which is a polyphenol found in curry spice.
Experimental data showed that the system was adequate for solubility measurements. Moreover, the system was valid as well to provide information about CXLs density values, which are also of high importance to study the solvent behaviour. The obtained results in this thesis validated the idea that high contents of ethanol in CO2, at relatively moderate pressures and temperatures, led to higher solubility values of the analyte in CXLs than in a system composed by pure CO2. (Less)
Please use this url to cite or link to this publication:
author
Coto Acosta, Mar LU
supervisor
organization
course
KEMP36 20161
year
type
H2 - Master's Degree (Two Years)
subject
keywords
Carbon-dioxide expanded liquids (CXLs), Solubility, Density, Antioxidants, analytical chemistry, analytisk kemi
language
English
id
8901287
date added to LUP
2017-02-03 13:40:33
date last changed
2017-02-03 13:40:33
@misc{8901287,
  abstract     = {Antioxidants are compounds present in plant, fruit, and vegetables, and they are known for their medicinal benefits such as anti-carcinogenic and anti-fungicidal activity. Most commonly used methods for extractions of such compounds are lengthy due to mass transfer limitations. This study proposes the use of carbon-dioxide expanded liquids (CXLs) as solvent to improve these limitations. Such solvents, considered as green solvents because of its inertness, odourless and low toxic properties, present tunable physical properties, such as low viscosity and high diffusivity rates. The solubility of CO2 in ethanol determines the volume expansion and, depends on temperature and pressure. Hence, the acquisition of solubility data of analyte in CXLs and the density of such mixtures will be valuable for an optimum extraction of antioxidant from complex solid samples. Aiming to study these properties, a system able to perform measurement of solubility and phase equilibria was developed. The equipment consists of a high pressure view cell connected in-line to a densitometer and a supercritical fluid chromatograph with a photodiode array detector. Validation of such equipment was performed with curcumin, a polyphenol extracted from Turmeric (Curcuma longa L.), 200 bar and 40 ºC in 92 % CO2 and 8 % ethanol, giving a solubility of 0.37 x 102 (molar fraction) , while in literature the observed value is 0.41 x 102 (molar fraction). Solubility measurements were successfully determined for curcumin at 200 bar, 35 ºC and at different content of ethanol in the mixture– from 50 to 90 %. Densities for such mixtures were also studied. Results have shown that the solubility of curcumin increases with the amount of ethanol as expected. Another polyphenol studies is quercetin, which it was found to be higher in solubility than curcumin. In general terms, the developed equipment has shown to be efficient for the established purpose. Further investigations are needed to confirm the range of applicability.},
  author       = {Coto Acosta, Mar},
  keyword      = {Carbon-dioxide expanded liquids (CXLs),Solubility,Density,Antioxidants,analytical chemistry,analytisk kemi},
  language     = {eng},
  note         = {Student Paper},
  title        = {Application of CO2 expanded liquids as green solvents for the extraction of antioxidants},
  year         = {2016},
}