Food Lipids: Chemistry, Nutrition, and Biotechnology

8
Recovery, Refining, Converting, and
Stabilizing Edible Fats and Oils
LAWRENCE A. JOHNSON
Iowa State University, Ames, Iowa
I. INTRODUCTION
Processing seeds or animal tissues into edible oils can be broken into four sets of
operations: recovery, refining, conversion, and stabilization. Oil recovery is often
referred to as extraction or crushing when processing plant sources and rendering
in the case of processing animal tissues. Oil extraction involves pressing the oilbearing
material to separate crude oil from the solids high in protein or washing
flaked or modestly pressed material with solvent, almost always hexane. The defatted
solids after pressing are known as cake and after solvent extraction as meal. The oil,
crude oil because it contains undesirable components, such as pigments, phosphatides,
free fatty acids, and off-flavors and off odors, must be refined to remove these
contaminants and produce high quality edible oils. Refined oils consist primarily
(>99%) of triglycerides and can be converted, usually by hydrogenation; but winterizing,
fractional crystallization, and interesterification should also be considered
conversion processes because they achieve different properties from the original oil,
such as converting liquid oil into semisolid or solid fats. Plasticizing, tempering, and
stehling are operations designed to stabilize crystal–oil mixtures used for shortenings
and margarines.
II. OIL RECOVERY
For several thousand years, fats and oils have been recovered from oil-bearing seeds,
fruits, and fatty animal tissues, and used for food, cosmetics, lubricants, and lighting
fluids. Of the more than several hundred plants and animals that produce fats and
Copyright 2002 by Marcel Dekker, Inc. All Rights Reserved.