Food Lipids: Chemistry, Nutrition, and Biotechnology

Accelerated solvent extraction (ASE) techniques have recently been introduced.
These use classical solvent systems to extract lipids, but under varying extraction
parameters such as temperature, pressure, and volume. ASE is also automated
[24,25]. The ASE process consumes a much lower solvent volume and time as lipid
is extracted at temperatures well above the boiling point of the solvent due to the
elevated pressure used in the process. This enhances solubilization and diffusion of
lipids from samples into the solvent, significantly shortening the extraction time and
solvent consumption. The fat could be extracted with no outflow of solvent (static
mode) or allowing fresh solvent to flow continuously through the sample (dynamic
mode) during extraction. Under elevated temperature and pressure, dissolved lipids
diffuse from the core to the surface of the sample particles and then are transferred
to the extraction solvent. Compressed gas then purges the solubilized fat into a
collection vessel and can then be quantified gravimetrically [7]. According to Schafer
[25], the content of fatty acids of the lipids extracted from muscle matrices using
ASE (Dionex 200 or 300 System, chloroform–methanol solvent system) was similar
or better in comparison with the conventional Folch extraction. The automated solvent
extractors contain microwave moisture analyzer to dry the sample before extraction,
redry to remove solvent and moisture, and to determine the percentage of
fat as weight loss due to the extraction process [2].
4. Methods Using Nonorganic Solvents
Due to environmental concerns and potential health hazards of organic solvents,
nonorganic solvents have become popular. The use of microwave digestion for isolating
lipids has recently been reported [26]. It is suggested that microwave energy,
by increasing the rotational force on bonds connecting dipolar moieties to adjacent
molecules, reduces the energy required to disrupt hydrophobic associations. Hydrogen
bonding, and electrostatic forces, thus helping to dissolve all kinds of lipids [26].
Microwave technology has allowed the development of rapid, safe, and cost-effective
methods for extracting lipids and does not require that samples be devoid of water
[27]. Performance of microwave lipid extraction was qualitatively (all lipid classes)
and quantitatively comparable to that of the conventional Folch method for various
biological samples [26].
Supercritical fluid extraction (SFE). When carbon dioxide is compressed at a
temperature (31.1�C) and pressure (72.9 atm) above its critical point, it doesn’t liquify
but attains a dense gaseous state that behaves like a solvent. Thus, it is called
supercritical CO2 (SC-CO2). Use of SC-CO2 for lipid extraction significantly reduces
the use of organic solvents, avoids waste disposal problems, eliminates the use of
potentially toxic and flammable solvents, and reduces the extraction time. Lipids so
extracted are not subjected to high temperatures during the extraction process.
Extraction using SC-CO2 yields a good recovery of nonpolar lipids including
esterified fatty acids, acylglycerols, and unsaponifiable matter. Complex polar lipids
are only sparingly soluble in SC-CO2. The polarity of SC-CO2 can be varied by
using an entrainer such as methanol, ethanol, or even water to improve the extraction
of polar lipids [28–31]. This technique has been used for the extraction of lipids
from various matrices, including dehydrated foods [32,33], meats [34–36], and fried
foods [37]. Particle size also affects lipid recovery because it influences the surface
area exposed to SC-CO2. High moisture content decreases contact between sample
and SC-CO2 as well as the diffusion lipids outside the sample [38]. The extracted
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