SHORTENING AND DIETARY FAT DEFINITIONS
May 1, 2005
Active Oxygen Method (AOM). This is a means of testing the stability of an oil or fat against oxidation. The sample is heated to 208°F (97.8°C), and air is bubbled through it. The time required to develop a peroxide content of 100 meq per kg is termed the AOM stability of the fat. This method is considered obsolete and is being replaced by oil stability index, or OSI (see below).
Cholesterol. Humans obtain cholesterol, which is in all animal tissue, in two ways: consumed in the diet (exogenous cholesterol) and synthesized by the body (endogenous cholesterol). High intake of dietary cholesterol has been associated with coronary heart disease.
Essential fatty acids. These are polyunsaturated fatty acids that cannot be synthesized by the body but are needed for human growth and development. Alpha-linolenic acid is a polyunsaturated (C18:3) omega-3 essential fatty acid and a precursor to the omega-3 fatty acids eicosapentaenoic acid C20:5 (EPA) and docosahexaenoic acid C22:6 (DHA). Linoleic acid is a polyunsaturated omega-6 essential fatty acid and a precursor of arachidonic acid C20:4 and a class of prostaglandins different from those produced by omega-3 fatty acids.
Fatty acid nomenclature. Three numbers are used in shorthand designation of natural fatty acids. The first is the number of carbon atoms in the chain, and the second is the number of double bonds. For example, C18:0 contains 18 carbon atoms and no double bonds (stearic acid). The third number, the number of carbon atoms between the last double bond and the methyl end of the chain, is the omega number, written using either the Greek letter omega (w) or as n-.
Hydrogenation. In the presence of a catalyst, hydrogen gas adds to a double bond, decreasing the degree of unsaturation of a fat or oil. The catalyst can also convert the natural cis double bond to the trans geometric isomer. Both changes raise the melting point of the fat and increase its stability to autoxidation.
Melting point. Fats do not have sharp melting points (m.p.) like a pure organic material. The complete, or capillary, melting point measures the disappearance of the last trace of cloudiness, corresponding to an SFC of 0. The Wiley m.p. is the temperature at which a disk of fat changes shape to a sphere (SFC of ~3). The dropping point, or Mettler m.p., is determined on a machine that records the temperature at which the fat is liquid enough to flow through a small orifice (SFC of ~1).
Monounsaturated fatty acids. These are fatty acids with one double bond, such as oleic acid. Although previous research suggested that monounsaturates had a neutral effect on serum cholesterol, recent preliminary studies indicate that monounsaturates may actually have a favorable effect.
Oil Stability Index (OSI). A newer, automated method for testing stability against oxidation. Air is bubbled through oil, usually at 230°F (110°C), and the time when rapid autoxidation begins is determined automatically. A 40-hour OSI is equivalent to a 100-hour AOM.
Omega-3 fatty acids. These are certain polyunsaturated fatty acids. Alphalinolenic acid is converted to EPA, a precursor of a class of prostaglandins that inhibit blood clotting (platelet aggregation). DHA is synthesized from EPA.
Polyunsaturated fatty acids. These are fatty acids with two or more double bonds, such as the essential fatty acids linoleic and alpha-linolenic acids.
Saturated fatty acids. These are fatty acids with no double bonds, such as stearic and palmitic acids. Studies show an association between increased intake of saturated fatty acids and increased serum cholesterol.
Solid Fat Index/Content (SFI, SFC). If measured using a dilatometer, the ratio of solid to liquid triglyceride in a shortening is called the Solid Fat Index (SFI). This is not always a true measure of percentage of solid fat, as a completely solid fat has an SFI of about 80. Pulsed nuclear magnetic resonance (pNMR) gives a more accurate estimation of true solid fat percentage and is termed Solid Fat Content (SFC).