Palm oil fractionationModification techniques like fractionation, interesterification (chemical or enzymatic) and hydrogenation allow proposing a large range of new fatty products. At a time when "trans" fatty acids are questioned, fractionation of fats and oils catches more and more interest; in this context, dry fractionation is by far the simplest and cheapest fractional crystallization technique (no chemicals, no effluent and no losses). The oil processing industry uses dry fractionation to extend the application of a whole variety of fatty matters as well as to replace, fully or partially, the chemical modifications. Due to the continuous developments of the dry fractionation process, a whole variety of products normally produced by solvent fractionation can now be obtained with a high degree of selectivity with dry fractionation. As the crystallization operates in the bulk, viscosity problems limit the degree of crystallization in one single step, and multi-step operations are currently used, giving rise to a wide range of fractions suitable for different applications. The secret is to combine proper crystal development with highly efficient separation by using membrane press filters allowing squeezing out the stearin cake for as much liquid occlusion (olein) as possible. The original booming of the dry fractionation process has helped mostly palm oil to conquer a strong position on the commodity market in one single stage; today, palm oil is without doubt the most widely fractionated oil. New demands for special cuts drifted the industry towards a more sophisticated approach: high-iodine value super and top oleins, palm red fractions (high carotene and tocopherol/tocotrienol contents) or solvent-free cocoa butter equivalents (palm mid fractions) are certainly what the future has in store.

Crude palm oil is rich in minor components that impart unique nutritional properties. The most relevant are tocopherols and tocotrienols (vitamin E) and carotenoids (a-and b-carotene). Palm oil is generally refined by the physical process, which is preferred over the chemical process since high acidity (up to 5%) can lead to excessive loss of neutral oil in the soapstock after alkali neutralization. The quality of the crude oil is to be considered as it can greatly affect the efficiency of the refining process and the quality of the end-products. The deterioration of bleachability index (DOBI) is a good indicator of the capability of palm oil to be successfully refined. Beside commodities, especially refined oils open a market for new high-quality products like golden palm oil, red palm oil, white soaps, fractionated products (CBE), etc. Optimization of the deodorization technology and of the process conditions for a maximal retention of natural characteristics without affecting the quality of the palm oil is an important challenge.

The influence of the refining process on the distribution of free and esterified phytosterols in corn, palm, and soybean oil was studied. Water degumming did not affect the phytosterol content or its composition. A slight increase in the content of free sterols was observed during acid degumming and bleaching due to acid-catalyzed hydrolysis of steryl esters. A significant reduction in the content of total sterols during neutralization was observed, which was attributed to a reduction in the free sterol fraction. Free sterols probably form micelles with soaps and are transferred into the soapstock. The steryl ester content remained constant during all neutralization experiments, indicating that hydrolysis of steryl esters did not take place during neutralization. During deodorization, free sterols are distilled from the oil, resulting in a gradual reduction in the total sterol content as a function of the deodorization temperature (220-260°C). A considerable increase in the steryl ester fraction was found during physical refining, probably owing to a heatpromoted esterification reaction between free sterols and FA.Paper no. J10068 in JAOCS 79, 947-953 (October 2002).

Fat blends, formulated by mixing a highly saturated fat (palm stearin or fully hydrogenated soybean oil) with a native vegetable oil (soybean oil) in different ratios from 10:90 to 75:25 (wt%), were subjected to chemical interesterification reactions on laboratory scale (0.2% sodium methoxide catalyst, time = 90 min, temperature = 90°C). Starting and interesterified blends were investigated for triglyceride composition, solid fat content, free fatty acid content, and trans fatty acid (TFA) levels. Obtained values were compared to those of low-and high-trans commercial food fats. The interesterified blends with 30-50% of hard stock had plasticity curves in the range of commercial shortenings and stick-type margarines, while interesterified blends with 20% hard stock were suitable for use in soft tubtype margarines. Confectionery fat basestocks could be prepared from interesterified fat blends with 40% palm stearin or 25% fully hydrogenated soybean oil. TFA levels of interesterified blends were low (0.1%) compared to 1.3-12.1% in commercial food fats. JAOCS 75, 489-493 (1998).

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sterols were separated by silica gel column chromatography upon elution with n-hexane/ethyl acetate (90:10 vol/vol) followed by n-hexane/diethyl ether/ethanol (25:25:50 by vol). Both fractions were saponified separately and the phytosterol content was quantified by GC. The analytical method for the analysis of esterified and free sterols had a relative standard deviation of 1.16% and an accuracy of 93.6-94.1%, which was comparable to the reference method for the total sterol analysis. A large variation in the content and distribution of the sterol fraction between different vegetable oils can be observed. Corn and rapeseed oils were very rich in phytosterols, which mainly occurred as steryl esters (56-60%), whereas the majority of the other vegetable oils (soybean, sunflower, palm oil, etc.) contained a much lower esterified sterol content (25-40%). No difference in the relative proportion of the individual sterols among crude and refined vegetable oils was observed.In vegetable oils, plant sterols mainly occur as free sterols or steryl esters of FA. The biosynthesis, biological function, and nutritional importance of phytosterols has recently been reviewed (1). The conventional method for sterol analysis involves a saponification of the TAG followed by an extraction of the unsaponifiable fraction with an organic solvent in order to determine the total sterol content (1). However, important information on the phytosterol fraction is lost through saponification. The steryl ester fraction is a complex mixture consisting of a variety of phytosterols esterified to various FA. The distribution of FA esterified to sterols differed considerably from the FA in the TAG of the vegetable oil. All steryl esters contained significantly higher levels of unsaturated FA compared to the corresponding TAG composition of the oil (2,3).Only a few literature reports are available on the combined quantification of free and esterified sterols. Methods reported so far have separated esterified and free sterols by either silica gel column chromatography, preparative TLC, or normalphase solid-phase extraction followed by saponification and GC quantification of both fractions (2-7). The esterified/free sterol content has been published for some vegetable oils (8).Some analytical methods have reported the quantification of steryl esters without saponification of the TAG. Steryl esters, sometimes in combination with free sterols, were isolated from TAG by TLC or normal-phase LC and quantified by GC or HPLC (3,(9)(10)(11)(12)(13). This direct analysis of the steryl ester fraction always resulted in an incomplete separation of the different steryl esters.In summary, few analytical reports deal with a separation of the esterified/free sterol fraction, and quantitative data on the free and esterified sterol content in vegetable oils are scarce. This study reports on the optimization and evaluation of an analytical method to determine the level of free and esterified sterols in vegetable oils followed by a quantification of the free and esterifie...

The effects of each individual step of the chemical refining process on major and minor components of rice bran oil were examined. In comparison with common vegetable oils, rice bran oil contains a significantly higher level of several bioactive minor components such as γ-oryzanol, tocotrienols, and phytosterols. Alkali treatment or neutralization results in a significant loss of oryzanol. In addition, it gives rise to a change in the individual phytosterol composition. After bleaching, some isomers of 24-methylenecycloartanol were detected. Because of their relatively high volatility, phytosterols and tocotrienols are stripped from the rice bran oil during deodorization and concentrated in the deodorizer distillate. At the same time, oryzanol is not volatile enough to be stripped during deodorization; hence, the oryzanol concentration does not change after deodorization. Complete refining removed 99.5% of the FFA content. Depending on the applied deodorization conditions, trans FA can be formed, but the total trans content generally remains below 1%.

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