For hexane, specific heat is 2. For MeTHF, specific heat is 1. Seeds were considered having a water content of 7. Meal was considered to have an average water content of Desolventation is made by indirect heating and direct steam injection. According to Schumacher [ 21 ], 0. By extrapolating it was considered that 0. The enthalpy of vaporization of condensed steam is lost during the drying step; in the study it was considered that it was consumed only the amount of steam required to reach For the miscella distillation, there is heat recovery from the desolventizer.
The gas that comes out the desolventizer passes through an exchange column to recover the condensation heat and evaporates a portion of the hexane from the miscella. Steam used for desolventization is 10 bar saturated steam and six bar saturated steam for distillation.
The energy needs for the preparation step do not vary from one case to another because no solvent is used. However for the extraction step, as the boiling point is higher for MeTHF than for hexane, more energy is required to attain the boiling temperature as well as more direct steam is required for stripping the residues. The same observation is made for the distillation of the miscella with small savings on the heating of the oil with MeTHF compared to hexane because it was considered that less solvent can be used thanks to better diffusivity.
In fact, extraction at higher temperature might be achieved by using the excess heat from the cake to preheat the solvent, and therefore the cake does not require a lot of cooling before extraction so a little heat will be saved for distillation. More interestingly, maintaining higher temperature between pre-press and extractor could avoid a possible resumption of the phospholipase activity and, in consequence, result in lower non-hydratable phosphorus concentration in extraction.
This part presents available data on the possible economic impact concerning the replacement of hexane by MeTHF in the rapeseed crushing process. On the basis of a consumption of 0. These costs are not taking into account the possible reductions of the solvent price in case of larger production. Nevertheless this additional oil generates an equivalent loss in the amount of cake.
Diffusivity of solvent may also have an impact. Diffusivity could have been extrapolated to an increase of the capacity of a factory but it is quite difficult at the present stage of knowledge. The practical consequences are an increase in the capacity of the extractor, which is usually the bottleneck.
It is finally a sum of the incremental costs of 4. The hypothesis that no disadvantage in oil acidity is made so it is likely there might be little change in refining costs.
Moreover, the use of a new solvent would probably imply a lower tolerance of solvent residues in products for food use compared to what is allowed with hexane. The economic study cannot rely only on technological data but should also take into account sanitary and regulatory aspects that will probably have a huge impact on the process and that are very difficult to anticipate and therefore to assess.
Rapeseed was coarsely ground less than 30 min before extraction. Oils were isolated from seeds by means of Soxhlet extraction [ 26 ]. They were then placed in the extraction chamber of a mL Soxhlet apparatus, see Figure 5 , fitted with a condenser, which was placed on a mL distillation flask containing mL of solvents n- hexane or MeTHF, respectively.
Thereafter, the cellulose thimble was cooled to room temperature in a desiccator and its content was then ground before being loaded again in the cellulose cartridge. After the extraction the content of the distillation flask was evaporated under reduced pressure. The weight of the rapeseed oil was determined and then used for calculating the yield of extracted oil.
All extractions were performed in triplicate and the mean values were reported. Results were obtained by gas chromatographic analysis in order to know the yields of extracted oils, i. The yield of extracts obtained by GC after trans-methylation of fatty acids was expressed as a percentage of the weight of extracted oil obtained after extraction relative to the weight of dry rapeseeds used for extraction, as described hereinafter,.
In order to study the industrial process and the transposition of scale, a laboratory scale of the pilot scheme was achieved.
Thereby, a special Soxhlet apparatus was manufactured by Legallais Montferrier-sur-Lez, France with a water jacket around the extraction chamber to set the temperature of the extraction as shown in Figure 5.
The residual oil in the matrix was then determined using the conventional Soxhlet extraction procedure described in Section 2. This ratio was selected to reproduce the conditions inside the extraction chamber that contains mL solvent once completely filled. In order to follow the kinetic, approximately 1 mL of sample was collected from the flask after 1, 3, 5, 10, 15, 20 and 30 min, then the same volume of sample was withdrawn every 30 min during 2 h of extraction.
The kinetics were established with mass difference. This percentage is then related to the total mass of extract knowing the initial mass of total used solvent linked to the volume of mL by the density and taking into account the mass of solvent and extract removed for the sampling.
In this device Figure 5 the solvent is forced to percolate through a layer of solid mm to continuously wash the matrix and solubilize oil contained into seeds. The miscella containing solvent and extracted oil is moved by a pump which circulates continuously through a heat exchanger. Trials were realized on 2 kg matrix with 1. This ratio was selected as it was calculated to simulate what is done in industrial plants with counter-current extractors [ 28 , 29 ].
Oil content in solid residue was then determined using the conventional Soxhlet extraction procedure described in Section 3. Samples were prepared from extracted oils using acid-catalyzed trans-methylation [ 30 ]. One point five mL of sodium chloride 0. The flask was stoppered and shaken vigorously during 30 s before centrifugation at rpm for 2 min. A small amount of the organic layer was removed and transferred into a vial before being injected directly in a gas chromatography.
Quantification was performed thanks to internal calibration. The internal standard was glyceryl tripheptanecanoate Sigma, Co. The densitometry data are reported as values which are expressed as percent of lipid class in total rapeseed lipids. The chemical structures of the solvents and solutes discussed in this article could be mutually transformed by JChemPaint version 3.
COSMO-RS is a quantum chemistry solvation model based on the prediction of chemical potential of a substance in the liquid phase [ 3 , 4 ]. The relative solubility is calculated from the following equation [ 33 ]:. Relative solubility is always calculated in infinite dilution. The logarithm of the best solubility is set to 0 and all other solvents are given relatively to the best solvent. The aim of the present study was to investigate the replacement of hexane for extraction of vegetable oil by bio-based, non-toxic and biodegradable solvent.
A solvent selection using HSP and COSMO-RS simulation tools as well as theoretical properties of candidate solvents showed that MeTHF is the most suitable solvent to replace hexane due to its properties to dissolve not only triglycerides but also the other classes of lipids such as sterols, tocopherols and tocotrienols.
The experimental laboratory study confirms these theoretical simulations. We compared hexane and MeTHF in terms of yield, selectivity, chemical composition, and kinetics and diffusion studies.
Pilot plant experimentation as well as energy and economic evaluation of the process prove that MeTHF could be a potential industrial alternative to hexane. National Center for Biotechnology Information , U. Int J Mol Sci. Published online Apr Find articles by Maryline Vian. Find articles by Farid Chemat. James H. Clark, Academic Editor. Author information Article notes Copyright and License information Disclaimer. Received Feb 26; Accepted Apr 9.
This article has been cited by other articles in PMC. Keywords: alternative solvent, solvent selection, bio-based solvent, MeTHF, extraction, kinetic parameters, economic evaluation. Note: In lieu of an abstract, this is the article's first page.
Cited By. This article is cited by 9 publications. Marcus J. Crompton , R. Hugh Dunstan. Evaluation of in-situ fatty acid extraction protocols for the analysis of staphylococcal cell membrane associated fatty acids by gas chromatography. Journal of Chromatography B , , ChemPhysChem , 17 24 , Snyder , Athina Chaidemenou , Raid G. Fatty acid microemulsion for the treatment of neonatal conjunctivitis: quantification, characterisation and evaluation of antimicrobial activity.
Drug Delivery and Translational Research , 6 6 , RSC Advances , 5 87 , Ganbavale , A. Valuable information about the lipid oxidation process is obtained by measuring changes in this profile with time, especially when peaks are identified using mass spectrometry or NMR.
It is possible to monitor the loss of reactants e. These measurements may be made on non-polar lipids extracted from the food, water-soluble reaction products present in the aqueous phase of a food or volatile components in the head-space of a food.
Lipid oxidation depends on the reaction between unsaturated fatty acids and oxygen. Thus it is possible to monitor the rate at which it occurs by measuring the uptake of oxygen by the sample as the reaction proceeds. Usually, the lipid is placed in a sealed container and the amount of oxygen that must be input into the container to keep the oxygen concentration in the head-space above the sample constant is measured.
The more oxygen that has to be fed into the container, the faster the rate of lipid oxidation. This technique is therefore an example of a measurement of the reduction in the concentration of reactants. Peroxides R-OOH are primary reaction products formed in the initial stages of oxidation, and therefore give an indication of the progress of lipid oxidation.
One of the most commonly used methods to determine peroxide value utilizes the ability of peroxides to liberate iodine from potatssium iodide. The lipid is dissolved in a suitable organic solvent and an excess of KI is added:. Once the reaction has gone to completion, the amount of ROOH that has reacted can be determined by measuring the amount of iodine formed. This is done by titration with sodium thiosulfate and a starch indicator:.
The amount of sodium thiosulfate required to titrate the reaction is related to the concentration of peroxides in the original sample as described earlier for the iodine value. There are a number of problems with the use of peroxide value as an indication of lipid oxidation. Firstly, peroxides are primary products that are broken down in the latter stages of lipid oxidation.
Thus, a low value of PV may represent either the initial or final stages of oxidation. Secondly, the results of the procedure are highly sensitive to the conditions used to carry out the experiment, and so the test must always be standardized. This technique is an example of a measurement of the increase in concentration of primary reaction products. Conjugated dienes absorb ultraviolet radiation strongly at nm, whereas conjugated trienes absorb at nm.
Thus oxidation can be followed by dissolving the lipid in a suitable organic solvent and measuring the change in its absorbance with time using a UV-visible spectrophotometer. In the later stages of lipid oxidation the conjugated dienes which are primary products are broken down into secondary products which do not adsorb UV-visible light strongly which leads to a decrease in absorbance. This method is therefore only useful for monitoring the early stages of lipid oxidation. This is one of the most widely used tests for determining the extent of lipid oxidation.
It measures the concentration of relatively polar secondary reaction products, i. The lipid to be analyzed is dissolved in a suitable non-polar solvent which is contained within a flask.
An aqueous solution of TBA reagent is added to the flask and the sample is shaken, which causes the polar secondary products to be dissolved in it.
After shaking the aqueous phase is separated from the non-polar solvent, placed in a test-tube, and heated for 20 minutes in boiling water, which produces a pink color. The intensity of this pink color is directly related to the concentration of TBA-reactive substances in the original sample, and is determined by measuring its absorbance at nm using a UV-visible spectrophotometer.
The principle source of color is the formation of a complex between TBA and malanoaldehyde , although some other secondary reaction products can also react with the TBA reagent. For this reason, this test is now usually referred to as the thiobarbituric acid reactive substances TBARS method. TBARS is an example of a measurement of the increase in concentration of secondary reaction products.
Rather than determining the extent of lipid oxidation in a particular food, it is often more important to know its susceptibility to oxidation.
Normally, oxidation can take a long time to occur, e. For this reason, a number of accelerated oxidation tests have been developed to speed up this process. These methods artificially increase the rate of lipid oxidation by exposing the lipid to heat, oxygen, metal catalysts, light or enzymes.
Even so there is always some concern that the results of accelerated tests do not adequately model lipid oxidation in real systems.
A typical accelerated oxidation test is the active oxygen method AOM. A liquid sample is held at 98 oC while air is constantly bubbled through it. Stability is expressed as hours of heating until rancidity occurs, which may be determined by detection of a rancid odor or by measuring the peroxide value. Another widely used accelerated oxidation test is the Schaal Oven Test.
A known weight of oil is placed in an oven at a specified temperature about 65 oC and the time until rancidity is detected is recorded by sensory evaluation or measuring the peroxide value. Characterization of Physicochemical Properties. In addition to their nutritional importance lipids are also used in foods because of their characteristic physicochemical properties, such as mouthfeel, flavor, texture and appearance. They are also used as heat transfer agents during the preparation of other foods, e.
It is therefore important for food scientists to have analytical techniques that can be used to characterize the physicochemical properties of lipids. The solid fat content SFC of a lipid influences many of its sensory and physical properties, such as spreadability , firmness, mouthfeel, processing and stability.
Food manufacturers often measure the variation of SFC with temperature when characterizing lipids that are used in certain foods, e. The solid fat content is defined as the percentage of the total lipid that is solid at a particular temperature, i.
A variety of methods have been developed to measure the temperature dependence of the solid fat content. The density of solid fat is higher than the density of liquid oil, and so there is an increase in density when a fat crystallizes and a decrease when it melts.
By measuring the density over a range of temperatures it is possible to determine the solid fat content - temperature profile:. The density is usually measured by density bottles or dilatometry. More recently, instrumental methods based on nuclear magnetic resonance NMR have largely replaced density measurements, because measurements are quicker and simpler to carry out although the instrumentation is considerably more expensive.
Basically, the sample is placed into an NMR instrument and a radio frequency pulse is applied to it. This induces a NMR signal in the sample, whose decay rate depends on whether the lipid is solid or liquid. The signal from the solid fat decays much more rapidly than the signal from the liquid oil and therefore it is possible to distinguish between these two components.
Techniques based on differential scanning calorimetry are also commonly used to monitor changes in SFC. These techniques measure the heat evolved or absorbed by a lipid when it crystallizes or melts. By making these measurements over a range of temperatures it is possible to determine the melting point, the total amount of lipid involved in the transition and the SFC-temperature profile. In many situations, it is not necessary to know the SFC over the whole temperature range, instead, only information about the temperature at which melting starts or ends is required.
A pure triacylglycerol has a single melting point that occurs at a specific temperature. Nevertheless, foods lipids contain a wide variety of different triacylglycerols , each with their own unique melting point, and so they melt over a wide range of temperatures.
Thus the "melting point" of a food lipid can be defined in a number of different ways, each corresponding to a different amount of solid fat remaining. Some of the most commonly used "melting points" are:.
This gives a measure of the temperature at which crystallization begins in a liquid oil. A fat sample is heated to a temperature where all the crystals are known to have melted e. The sample is then cooled at a controlled rate and the temperature at which the liquid just goes cloudy is determined. This temperature is known as the cloud point, and is the temperature where crystals begin to form and scatter light.
It is often of practical importance to have an oil which does not crystallize when stored at 0oC for prolonged periods. A simple test to determine the ability of lipids to withstand cold temperatures without forming crystals, is to ascertain whether or not a sample goes cloudy when stored for 5 hours at 0oC. These tests give a measure of the effect of heating on the physicochemical properties of lipids.
They are particularly important for selecting lipids that are going to be used at high temperatures, e. The tests reflect the amount of volatile organic material in oils and fats such as free fatty acids. The rheology of lipids is important in many food applications. Rheology is the science concerned with the deformation and flow of matter.
Most rheological tests involve applying a force to a material and measuring its flow or change in shape. Many of the textural properties that people perceive when they consume foods are largely rheological in nature, e. The stability and appearance of foods often depends on the rheological characteristics of their components. The flow of foods through pipes or the ease at which they can be packed into containers are also determined by their rheology.
Liquid oils are usually characterized in terms of their flow properties viscosity , whereas viscoelastic or plastic "solids" are characterized in terms of both their elastic elastic modulus and flow properties. A wide variety of experimental techniques are available to characterize the rheological properties of food materials. One of the most important rheological characteristics of lipids is their "plasticity", because this determines their " spreadability ".
The plasticity of a lipid is due to the fact that fat crystals can form a three-dimensional network that gives the product some solid-like characteristics.
Below a certain stress known as the "yield stress" the product behaves like a solid with an elastic modulus because the crystal network is not disrupted, but above this stress it flows like a liquid because the crystal network is continually disrupted.
Rheological techniques are therefore needed to measure the change in deformation of a lipid when stresses are applied. Analysis of Lipids 5. Introduction Lipids are one of the major constituents of foods, and are important in our diet for a number of reasons. Some of the most important properties of concern to the food analyst are : Total lipid concentration Type of lipids present Physicochemical properties of lipids, e. Properties of Lipids in Foods Lipids are usually defined as those components that are soluble in organic solvents such as ether, hexane or chloroform , but are insoluble in water.
Sample Selection and Preservation As with any analytical procedure, the validity of the results depends on proper sampling and preservation of the sample prior to analysis.
Determination of Total Lipid Concentration 5. Introduction It is important to be able to accurately determine the total fat content of foods for a number of reasons: Economic not to give away expensive ingredients Legal to conform to standards of identity and nutritional labeling laws Health development of low fat foods Quality food properties depend on the total lipid content Processing processing conditions depend on the total lipid content The principle physicochemical characteristics of lipids the " analyte " used to distinguish them from the other components in foods the "matrix" are their solubility in organic solvents, immiscibility with water, physical characteristics e.
Solvent Extraction The fact that lipids are soluble in organic solvents, but insoluble in water, provides the food analyst with a convenient method of separating the lipid components in foods from water soluble components, such as proteins, carbohydrates and minerals. Sample Preparation The preparation of a sample for solvent extraction usually involves a number of steps: Drying sample.
Batch Solvent Extraction These methods are based on mixing the sample and the solvent in a suitable container, e. Semi-Continuous Solvent Extraction Semi-continuous solvent extraction methods are commonly used to increase the efficiency of lipid extraction from foods. Continuous Solvent Extraction The Goldfish method is similar to the Soxhlet method except that the extraction chamber is designed so that the solvent just trickles through the sample rather than building up around it. Accelerated Solvent Extraction The efficiency of solvent extraction can be increased by carrying it out at a higher temperature and pressure than are normally used.
Supercritical Fluid Extraction Solvent extraction can be carried out using special instruments that use supercritical carbon dioxide rather than organic liquids as the solvent. Nonsolvent Liquid Extraction Methods. Babcock Method A specified amount of milk is accurately pipetted into a specially designed flask the Babcock bottle. Gerber Method This method is similar to the Babcock method except that a mixture of sulfuric acid and isoamyl alcohol, and a slightly different shaped bottle, are used.
Detergent Method This method was developed to overcome the inconvenience and safety concerns associated with the use of highly corrosive acids. Instrumental methods The are a wide variety of different instrumental methods available for determining the total lipid content of food materials. Measurement of bulk physical properties Density: The density of liquid oil is less than that of most other food components, and so there is a decrease in density of a food as its fat content increases.
Thus the lipid content of foods can be determined by measuring their density. Electrical conductivity : The electrical conductivity of lipids is much smaller than that of aqueous substances, and so the conductivity of a food decreases as the lipid concentration increases. Measurements of the overall electrical conductivity of foods can therefore be used to determine fat contents. Ultrasonic velocity: The speed at which an ultrasonic wave travels through a material depends on the concentration of fat in a food.
Thus the lipid content can be determined by measuring its ultrasonic velocity. This technique is capable of rapid, nondestructive on-line measurements of lipid content. Measurement of adsorption of radiation UV-visible: The concentration of certain lipids can be determined by measuring the absorbance of ultraviolet-visible radiation. The lipid must usually be extracted and diluted in a suitable solvent prior to analysis, thus the technique can be quite time-consuming and labor intensive.
Infrared: This method is based on the absorbance of IR energy at a wavelength of 5. IR is particularly useful for rapid and on-line analysis of lipid content once a suitable calibration curve has been developed. Nuclear Magnetic Resonance : NMR spectroscopy is routinely used to determine the total lipid concentration of foods.
The lipid content is determined by measuring the area under a peak in an NMR chemical shift spectra that corresponds to the lipid fraction. Lipid contents can often be determined in a few seconds without the need for any sample preparation using commercially available instruments. X-ray absorption : Lean meat absorbs X-rays more strongly than fat, thus the X-ray absorbance decreases as the lipid concentration increases. Commercial instruments have been developed which utilize this phenomenon to determine the lipid content of meat and meat products.
Measurement of scattering of radiation Light scattering: The concentration of oil droplets in dilute food emulsions can be determined using light scattering techniques because the turbidity of an emulsion is directly proportional to the concentration of oil droplets present. Ultrasonic scattering: The concentration of oil droplets in concentrated food emulsions can be determined using ultrasonic scattering techniques because the ultrasonic velocity and absorption of ultrasound by an emulsion is related to the concentration of oil droplets present.
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