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"1,3 diglyceride

"1,3 diglyceride meat fats are chemically refined, but for some vegetable oils, notably coconut and palm, physical refining is more economical. The choice is generally determined by the convenience and economics of the process.

Chemical, or caustic refining, is intended to remove most of the free fatty acids present in the crude oils. The process consists of treating the crude with an alkali solution, which converts the free fatty acids to soap. These soaps are removed by centrifugation and water washing. Phospholipid, mucilagenous, and proteinaceous materials are also removed in this step. Caustic strength, temperature, mixing, contact time, and removal are critical process parameters.

The residual moisture is removed by vacuum drying prior to bleaching. The natural pigments, carotenes and chlorophylls, are removed by physical absorption on acid-activated clay or bleaching earth. Other absorbent materials such as activated carbon may also be used in specific situations. The critical variables are absorbent level, contact time, temperature, and removal of the spent absorbent. Typically, hydrogenation follows bleaching. Hydrogen is added to unsaturated fatty acids in this heterogeneous reaction with gaseous hydrogen and catalyst, usually nickel although other precious metals may be used. Criti cal parameters are reaction time, temperature, pressure, catalyst type and amount, and gas purity. Vessel design to provide effective mass and heat transfer is also critical. Less commonly, the oil may be bleached again after hydrogenation.

Hydrogenation raises the melting point of the triglyceride mixture, thus altering physical properties. It also improves oxidative and thermal stability by reducing the number of labile, polyunsaturated reaction sites in the fatty acids of the triglyceride. Hydrogenation allows the processor to differentiate products for their various applications. A processor may make a full range of products, from salad oils to solid frying shortenings, margarines to bakery shortenings, by hydrogenating and blending various oils.

Deodorization typically follows hydrogenation or bleaching if natural liquid oil is desired. The process is a high-temperature, vacuum, steam distillation that removes residual fatty acids as well as undesirable flavor and odor compounds. This step will also remove a small portion of the natural antioxidants. The high-temperature exposure also reduces the color due to transformation of the red and yellow pigments into nonchromophores. Key elements are temperature, vacuum, steam rate, and exposure time. Again, vessel design is critical to provide effective and efficient heat and mass transfer.

Liquid oils may be packaged directly after deodorization, but fluid or plastic shortenings are usually votated, or crystallized, after deodorization. The blended, melted product is fed under pressure to a scraped-surface heat exchanger at slightly above its melting point. The product is chilled creating crystal nuclei, which are allowed to grow slowly for a controlled time in a mildly agitated vessel, commonly referred to as a B unit. Nitrogen may be added to gasify a solid shortening, providing a whiter, more plastic product. Proper crystal conversion may require tempering. Liquid products may be tempered in process, whereas solids are typically stored for 24 to 48 h at their tempering temperature. Key parameters are flow rate, temperature, and tempering conditions. Control of crystal structure is essential for functional bakery shortenings.

Other Processes

There are other specialized processing steps. The most notable are winterization, fractionation, transesterification, interesterification, and directed interesterification. Winterization and fractionation separate melting fractions by cooling the shortening and separating the solids that crystallize. Processors use winterization to provide stable salad oils. Fractionation consists of cooling the oil and separating the solids a number of times to obtain various melting fractions. These are used to create hard butters (cocoa butter substitutes) for coating applications and high stability oils. These processes may employ a solvent (hex-ane or acetone) to improve the separation, which is commonly referred to as solvent winterization or solvent fractionation (24).

Transesterification, a type of interesterification, is a process that rearranges or redistributes the fatty acids on the glycerine backbone of the triglyceride. Processors may select conditions to distribute the fatty acids more randomly, thus modifying the physical properties of the shortening. This process does not create a significant level of fatty acid isomers (trans) like hydrogenation. Hydrogenation may be combined before or after the process to allow further modification of the shortening.

Interesterification involves two or more oil sources, randomizing the fatty acids of the source triglycerides. By cooling and removing the higher-melting triglycerides the reaction can continue with the remaining components redirecting the interesterification. This process, used to provide relatively pure triglycerides, is called directed interesterification (25-27). If excess glycerol is present, monoglycerides and diglycerides are formed. The relative amounts of each at equilibrium are a function of the ratio of fatty acids available to glycerol (28). This is commonly called glycerolysis.

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