Bleaching soybean oil

The effect of container size on the oxidative deterioration of refined, bleached soybean oil stored at 48.9 °C (120 °F) for 5 weeks is shown in Figure 17. The results clearly demonstrate that oxidation is not only a function of time and temperature but also of the surface area. Figure 17 shows that as the container size increases, the surface-to-volume ratio decreases and peroxide development is an approximately linear function of surface-to-volume ratio. 

Figure 17. Effect of container size on the oxidative deterioration of refined, bleached soybean oil stored at 49° C for 5 weeks.

The oil normally used for hydrogenation is of caustic refined and bleached quality. With the increase of physical refining, refiners with no caustic refining facility must decide from the quality of the oil whether to use a pretreated or fully refined feedstock. Ong (1979) suggested the following quality for neutralized and bleached soybean oil for hydrogenation ... 

Table 8.1. Effect of storing refined and bleached soybean oil in tanks with air or nitrogen atmospheres ...

These include beeswax (find ones that aren t bleached or tinted with artificial colors), soy (made from soybean oil), bayberry, and tapioca wax candles. It s easy to find good ones online. Debra Lynn Dadd, the author of Home Safe Home, maintains a comprehensive list of candle companies on her Web site www.debraslist.com. 

The volatile peroxides, other oxidation decomposition products, and odiferous compounds form reduced-boiling point azeotropes with water in the steam, at high temperatures, 250-260°C/482-500°F, and very low absolute pressures ( 3 mbar). This is above the smoke point of soybean oil, but below the flash point, and oxygen must be excluded. Considerable heat bleaching of yellow-red carotenoids also occurs at this temperature. Typically the deodorization process requires 20-40 min after come-up time, uses 0.5-2.0 percent spaiged steam (the higher level if tocopherols are recovered), operates at between 2 and 4 mbar, and produces a product with about 0.03-0.05 percent FFA.143... 

Active Oxygen Method for Fat Stability (AOM) (Cd 12-57) determines the time (in hours) for a sample of fat or oil to attain a predetermined peroxide value (PV) under the conditions of the test. The method is used to estimate the comparative oxidative stability of fats and oils. The method has been placed in surplus, in favor of Cd 12b-92 (Oil Stability Index), but retains official status and is still used in domestic industry. p-Anisidine Value (AV) (Cd 18-90) determines the amount of aldehydes (principally 2-alkenals and 2,4-dienals) in animal and vegetable fats and oils. These are degradation products of peroxides, which are not removed by bleaching. Some fats and oils chemists propose increased use of this method in purchase specifications. Bleaching Test for Soybean Oil (Cc 8e-s63) determines the color of a sample of soybean oil after treatment with a specified bleaching earth. Specific methods exist for other oil species. 

Winterizing is not practiced so widely in hot countries and its application is restricted mainly to sunflower, maize, cotton, ohve, ricebran, and partially hydrogenated soybean oils. The feedstock of the winterizing plant is usually bleached oil, sometimes neutralized or deodorized oil. The winterizing process is conducted in four steps ... 

The stability of canola oil is limited mostly by the presence of linolenic acid, chlorophyll, and its decomposition products and other minor components with high chemical reactivity, such as trace amounts of fatty acids with more than three double bonds. These highly unsaturated fatty acids can possibly be formed during refining and bleaching (52). The presence of 7% to 11% of linolenic acid in the acylglyce-rols of canola oil places it in a similar category with soybean oil with respect to flavor and oxidative stability. The deterioration of flavor as the result of auto -and photo-oxidation of unsaturated fatty acids in oils and fats is referred to as oxidative rancidity. 

USA-ASTM standard for 100% pure biodiesel is similar in many respects (146), but it is written for the use of soybean oil as the main starting material. Canola oil for methyl ester production must either be degummed (<20 mg/kg of phosphorus), or in addition, must be alkali refined and bleached, depending on the methyl ester production process requirements (148). 

Refined, bleached, partially hydrogenated, winterized, and deodorized, pure soybean oil. 

Fluidizing. Fluidizing additives such as soybean oil, fatty acids, or calcium chloride can be added to adjust the viscosity. The viscosity of dried crude lecithin can also be decreased by warming it to a maximum of 60°C. The dried crude lecithin product (unbleached or bleached) can also be used to prepare a variety of grades of lecithin by removing the oil to increase the phospholipid content, or by separating the oil-free lecithin into alcohol-soluble and alcohol-insoluble fractions. 

Oxidation has an important effect on the color of fats and oils. Although oxidation bleaches the carotenoid pigments, it tends to develop the color of other types of coloring material and, in certain cases, even develops colored compounds of qui-noid nature from the fatty acids or acylglycerols of the oils. Cottonseed and, in certain cases, soybean oil are subject to marked darkening upon oxidation. The effect of oxidation or aeration on the color stability of oils is shown in Figure 7 (7). 

Prime concerns in storage of crude and once-refined soybean oils include increases in moisture and volatile matter, color after refining or bleaching, peroxide value, free fatty acids, and refining losses. Aside from possible effects on flavor and oxidative stability, many of these quality factors also affect the commercial value of oil in trading channels. With the exception of peroxide values and refined color, the other quality factors above are written into specifications for oils sold under trading rules of the National Soybean Processors Association (NSPA) (67). 

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