ABSTRACT
I. Introduction .......................................................................................................................... 132 II. Extraction of Lipids from Foods and Biological Materials .................................................. 132
A. Sample Preparation ...................................................................................................... 133 B. Pretreatments ................................................................................................................ 134
1. Drying .................................................................................................................... 134 2. Particle Size Reduction .......................................................................................... 134 3. Acid/Alkali Hydrolysis ........................................................................................... 134
C. Lipid Extraction with Solvents ..................................................................................... 135 1. Properties of Solvents and Their Mode of Extraction ............................................ 135 2. Extraction Methods with Single Organic Solvent .................................................. 136 3. Methods Using Organic Solvent Combination ....................................................... 136 4. Switchable Polarity Solvent .................................................................................... 138 5. Methods Using Nonorganic Solvents ..................................................................... 138
D. Lipid Extraction without Solvents ................................................................................ 140 1. Acid Digestion Methods ......................................................................................... 140 2. Detergent Method ................................................................................................... 140 3. Physical Methods ................................................................................................... 140 4. Enzymatic Method ................................................................................................. 140
E. Removal of Nonlipid Contaminants from Lipid Extracts and Other Practical Considerations .............................................................................................................. 141
III. Indirect Methods of Total Lipid Determination ................................................................... 142 A. Density Measurement ................................................................................................... 142 B. Dielectric Method ......................................................................................................... 142 C. Near-Infrared Spectroscopy ......................................................................................... 142 D. Fourier Transform Ion Cyclotron Resonance Mass Spectrometry ............................... 142 E. Low-Resolution Nuclear Magnetic Resonance Spectroscopy ...................................... 143 F. Turbidimetric/Colorimetric Methods ........................................................................... 143 G. Ultrasonic Method ........................................................................................................ 143 H. X-Ray Absorption......................................................................................................... 143 I. Flow Cytometry ........................................................................................................... 144
IV. Analysis of Lipid Extracts .................................................................................................... 144 A. Bulk Oil Properties ...................................................................................................... 144
1. Degree of Unsaturation .......................................................................................... 144 2. Free Fatty Acid Content ......................................................................................... 145 3. Oxidative Stability and Oxidation Products........................................................... 145 4. Refractive Index ..................................................................................................... 145 5. Saponication Value ............................................................................................... 145 6. Solid Fat Index ....................................................................................................... 145
Lipids are among the major components of food of plant and animal origin. There is no precise denition available for the term “lipid”; however, it usually includes a broad category of compounds that have some common properties and compositional similarities. Lipids are materials that are sparingly soluble or insoluble in water, but soluble in selected organic solvents such as benzene, chloroform, diethyl ether, hexane, and methanol. Together with carbohydrates and proteins, lipids constitute the principal structural components of tissues. However, the common and unique features of lipids relate to their solubility rather than their structural characteristics [1]. Many classication systems have been proposed for lipids. From the nutrition point of view, according to the National Academy of Sciences’ report on nutrition labeling, fats and oils are dened as the complex organic molecules that are formed by combining three fatty acid molecules with one molecule of g lycerol [2]. As indicated in Table 5.1 [3-5], lipids are generally classied as simple and compound (complex) or derived lipids according to the Bloor [3] classication.
