chapter  8
Recovery, Refining, Converting, and Stabilizing Edible Fats and Oils
Pages 40

I. Introduction.......................................................................................................................... 206 II. Oil Recovery ........................................................................................................................ 206

A. Extraction of Oil from Oilseeds................................................................................... 207 1. Seed Storage ......................................................................................................... 207 2. Cleaning ................................................................................................................ 211 3. Dehulling .............................................................................................................. 212 4. Hard Screw Pressing............................................................................................. 212 5. Prepress Solvent Extraction .................................................................................. 214 6. Direct Solvent Extraction...................................................................................... 214 7. Meal Grinding....................................................................................................... 219 8. Oil and Meal Storage............................................................................................ 219

B. Extraction of Oil-Bearing Fruits .................................................................................. 219 C. Recovery of Animal Fats and Marine Oils.................................................................. 221

1. Wet Rendering ...................................................................................................... 221 2. Dry Rendering ...................................................................................................... 221

III. Refining................................................................................................................................ 221 A. Background.................................................................................................................. 221 B. Degumming ................................................................................................................. 222 C. Neutralization (Alkali Refining) .................................................................................. 224 D. Miscella Refining (Neutralization) .............................................................................. 227 E. Drying .......................................................................................................................... 227 F. Bleaching ..................................................................................................................... 227 G. Dewaxing ..................................................................................................................... 229 H. Deodorization............................................................................................................... 229 I. Physical Refining ......................................................................................................... 230

IV. Conversion ........................................................................................................................... 231 A. Background .................................................................................................................. 231 B. Winterization and Fractional Crystallization ............................................................... 232

1. Winterization......................................................................................................... 232 2. Fractional Crystallization...................................................................................... 232

C. Hydrogenation.............................................................................................................. 233 1. Process .................................................................................................................. 233 2. Selectivity ............................................................................................................. 235

235 4. Effects on Physical and Functional Properties ..................................................... 236

D. Interesterification.......................................................................................................... 236 V. Stabilizing Physical Forms .................................................................................................. 237

A. Crystallizing ................................................................................................................. 238 1. Plasticizing ............................................................................................................ 238 2. Stehling ................................................................................................................. 238

B. Postprocessing Tempering ........................................................................................... 238 VI. Prospects for Improved Processes ....................................................................................... 239

A. Expander Preparation................................................................................................... 239 B. Alternative Solvents for Extraction ............................................................................. 239 C. Membrane Filtration .................................................................................................... 240 D. Enzymatic Degumming ............................................................................................... 240 E. Supercritical Fluid Refining......................................................................................... 240 F. Bleaching with Silica Gel ............................................................................................ 240

References ..................................................................................................................................... 241

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 oil-bearing 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 highquality 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.