Edible deodorizing

Fig. 6. Schematic outline for manufacture of edible soybean oil products, where D = deodorization, W = winterization, and S = solidification (73).

The supercritical fluid extraction of oil seeds has been investigated extensively by several authors [34,98]. Possible applications of supercritical fluids in the edible-oil industry include deacidification, deodorization, and fractionation of crude oils and chemical conversion (like hydrogenation, and enzymatic reactions). 

Leon-Camacho, M., Ruiz-Mendez, M.V., Graciani-Constante, M., Graciani-Costante, E. (2001) Kinetics of cis-trans isomerization of linoleic acid in the deodorization and/or physical refining of edible fats. Eur. J. Lipid Sci. Technol., 103, 85-92. 

Figure 4.4 shows the different stages in seed preparation and a classical chemical refining process. The general methods employed to produce edible oils suitable for human consumption consist of (a) seed preparation, (b) extraction, (c) degumming, (d) neutralization, (e) bleaching, (f) deodorization, (g) hydrogenation, and sometimes winterization. 

The removal of the free fatty acids in the bleached oil is done by steam distillation in a deodorizer. This, simultaneously, deodorizes the oil. Because deodoriza-tion is, also, the last process normally carried out on edible oils, this step may be delayed until other processes, such as hydrogenation of the oil, have been done. 

Experience has shown that edible fats and oils flavor and odor removal correlates well with the reduction of FFA. The odor and flavor of an oil with a 0.1 % FFA will be eliminated when the FFA is reduced to 0.01% to 0.03%, assuming a zero peroxide value. Therefore, all commercial deodorization consists of steam stripping the oil for FFA removal. Typical conditions practiced in the United States for the three deodorizer system types are shown in Table 23. The four interrelated operating variables that influence deodorizer design are vacuum, temperature, stripping rate, and retention time at deodorization temperatures. 

Deodorization Process Control. Deodorization is the last processing step, in which flavor, odor, and many of the stability qualities of an edible fat and oil product can be controlled. To produce quality deodorized products, attention must be focused on all of the factors involved with the process. The deodorization physical process removes the volatile, odoriferous materials present in the oils. The other factors that influence the quality of the deodorized oil products are as follows (106) ... 

Two methods, namely physical rehning and chemical rehning, are available for refining crude palm oil. They differ basically in the manner in which the free fatty acids are removed. Physical rehning has become the major processing route because of its cost effectiveness, efficiency, and simple effiuent treatment (39). Both processes are able to produce rehned, bleached, and deodorized (RBD) palm oil of desirable quality and stability suitable for edible purposes (40). The unit operations involved in these two processes and the components removed are shown in Figure 12 and Table 31, respectively. 

The salad oil may contain properly refined and deodorized cottonseed, corn, peanut, soybean, sesame, sunflower, or safflower vegetable oils or a mixture of these oils. Olive oil shall not be used. Edible vegetable oils not specified may also be used provided they are in accordance with good commercial practice. Specifications per announcement PV-50-1 dated June 17, 1976, issued by Agricultural Stabilization and Conservation Service, US. Department of Agriculture, Shawnee Mission, Kansas. 

Crude citrus seed oils need to be refined before use as edible oils. Only triacylglycerols, diacylglycerols, and polar lipids remain after degumming, refining, bleaching, and deodorization. However, trace amounts of phosphatides (lecithin) and plant sterols may also remain in the oil (37). 

Figure 4. Schematic for deodorizer oii storage. (Copyrighted by MG Edible Oil Consulting, Int l.).

Typically the last step in the edible oil refinery is deodorization, and this process is included in almost every refining operation, regardless of the other unit operations selected. While in the past limited natural fats could be utilized as edible products (such as butter and animal fats), most oils used today come from sources having natural components that if not removed impart objectionable flavors and tastes. These oils contain not only flavor bodies that must be eliminated to produce a palatable product but other unit operations, such as hydrogenation, impart a negative flavor and color that must be removed in the deodorizer. Shelf life and color are also important considerations upon which the deodorizer has a direct impact. 

Activity Coefficient a The efficient removal of volatile substances during edible oil deodorization depends not only on their vapor pressure but also on their concentration in the oil. The theoretical principle of the deodorization process has already been described in many publications (2-4). All calculations start from the basic laws of Raoult and Dalton, which are valid for ideal mixtures. However, in practice, the mixture of a fatty acid and a vegetable oil has a nonideal behavior. Consequently, a so-called activity coefficient a was introduced and Raoult s law may be written as follows ... 

Figure 11. Examples of external and Internal heat exchangers used in edible oil deodorization (Alfa Laval, Clat, De Smet).

Figure 16. Vacuum steam ejector system with barometric condensers used in edible oil deodorization (Kdrting).

In recent years, new developments in deodorization technology were mainly determined by the strong demand from edible oil refiners to reduce the capital and operating cost of deodorizers and the increased importance of the nutritional aspects of food oils and fats. 

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