402
Structural Characterization of Lipids
Oils and fats are of great economic importance as agricultural products, and they are
major items of international commerce. They are ingredient in most of foods. Fat
amounts to almost 40% of dietary calories in developed countries, and its composition is obviously vital to good nutrition. In addition, fats contribute greatly to the
palatability, taste and structure of foods (Christie and Han 2010). The term lipids
includes organic compounds such as fats, vegetable oils, waxes, cholesterol, phospholipids, steroids, and fat-soluble vitamins (A, D, E, and K). Though lipids are
group of amphiphatic molecules (containing both components of hydrophilic and
hydrophobic regions within the molecule), they are generally hydrophobic due
largely in part to their large proportion of hydrocarbons to polar regions (due to
oxygen containing functional groups). Therefore, lipids are insoluble in water but
soluble in non-polar solvents such as benzene and chloroform. The hydrophobic
nature of the molecule strongly determines the structures these molecules assume in
nature. Being structurally diverse, lipids have a variety of biochemical functions,
including structure, energy, energy storage, and signaling (steroids and
eicosanoids).
Lipids are an extremely varied group of compounds consisting of tri-, di- and
mono acylglycerols, free fatty acids, phospholipids, sterols, carotenoids and vitamins A and D. Fatty acids differ in their structure due to chain lengths, branching,
unsaturation, and positions on the glycerol molecule. Even a lipid which consists of
only triacylglycerols may contain enormous number of different chemical species.
It is essential for any food scientists to know and to be able to specify the concentration of different types of lipid molecules present, as well as the total lipid
concentration.
The study of lipids has assumed considerable importance with the recognition
that they are involved in many vital biological processes in animals, plants and
microorganisms. Organic solvents are employed to separate lipids from proteins,
carbohydrates and water soluble metabolites. The lipid composition of cells and
membranes can differ significantly with respect to lipid group, phospholipids class
and acyl group identity. Lipids are made of diverse combination of chemicals, they
also vary in terms of the lipid type and distribution and these play a important role
in determining their nutritional value, purity and its various other characteristic.
Therefore, it has become a necessity for scientists and legal bodies to acquire a
thorough knowledge about the various classes of lipids (McClements 2003).
Sample preparation is the vital part in most method to analyze lipids. It is imperative that during the extraction of lipids due care needs to be taken to prevent lipid
conversion to other forms. Production of free fatty acids due to hydrolysis needs to
be prevented as quickly as possible. Extraction should cause as less oxidation as
possible (Greenfield and Southgate 2003). Extraction in chloroform, chloroformmethanol and hexane-isopropanol is preferred. Storage of sample in cold at −20 °C
is preferred (AAFCO 2014). The choice of the method depends on the type of food
and lipid to be examined, however every available method has its advantage and
disadvantage (Greenfield and Southgate 2003).
S. Asokapandian et al.
Structural Characterization of Lipids
Oils and fats are of great economic importance as agricultural products, and they are
major items of international commerce. They are ingredient in most of foods. Fat
amounts to almost 40% of dietary calories in developed countries, and its composition is obviously vital to good nutrition. In addition, fats contribute greatly to the
palatability, taste and structure of foods (Christie and Han 2010). The term lipids
includes organic compounds such as fats, vegetable oils, waxes, cholesterol, phospholipids, steroids, and fat-soluble vitamins (A, D, E, and K). Though lipids are
group of amphiphatic molecules (containing both components of hydrophilic and
hydrophobic regions within the molecule), they are generally hydrophobic due
largely in part to their large proportion of hydrocarbons to polar regions (due to
oxygen containing functional groups). Therefore, lipids are insoluble in water but
soluble in non-polar solvents such as benzene and chloroform. The hydrophobic
nature of the molecule strongly determines the structures these molecules assume in
nature. Being structurally diverse, lipids have a variety of biochemical functions,
including structure, energy, energy storage, and signaling (steroids and
eicosanoids).
Lipids are an extremely varied group of compounds consisting of tri-, di- and
mono acylglycerols, free fatty acids, phospholipids, sterols, carotenoids and vitamins A and D. Fatty acids differ in their structure due to chain lengths, branching,
unsaturation, and positions on the glycerol molecule. Even a lipid which consists of
only triacylglycerols may contain enormous number of different chemical species.
It is essential for any food scientists to know and to be able to specify the concentration of different types of lipid molecules present, as well as the total lipid
concentration.
The study of lipids has assumed considerable importance with the recognition
that they are involved in many vital biological processes in animals, plants and
microorganisms. Organic solvents are employed to separate lipids from proteins,
carbohydrates and water soluble metabolites. The lipid composition of cells and
membranes can differ significantly with respect to lipid group, phospholipids class
and acyl group identity. Lipids are made of diverse combination of chemicals, they
also vary in terms of the lipid type and distribution and these play a important role
in determining their nutritional value, purity and its various other characteristic.
Therefore, it has become a necessity for scientists and legal bodies to acquire a
thorough knowledge about the various classes of lipids (McClements 2003).
Sample preparation is the vital part in most method to analyze lipids. It is imperative that during the extraction of lipids due care needs to be taken to prevent lipid
conversion to other forms. Production of free fatty acids due to hydrolysis needs to
be prevented as quickly as possible. Extraction should cause as less oxidation as
possible (Greenfield and Southgate 2003). Extraction in chloroform, chloroformmethanol and hexane-isopropanol is preferred. Storage of sample in cold at −20 °C
is preferred (AAFCO 2014). The choice of the method depends on the type of food
and lipid to be examined, however every available method has its advantage and
disadvantage (Greenfield and Southgate 2003).
S. Asokapandian et al.