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Vronique GibonWim De GreytMarc Kellens

De Smet Technologiesand Services,Zaventem, Belgium

Palm oil refining

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- andb-carotene). Palm oil is generally refined by the physical process, which is preferredover the chemical process since high acidity (up to 5%) can lead to excessive loss ofneutral oil in the soapstock after alkali neutralization. The quality of the crude oil is to beconsidered as it can greatly affect the efficiency of the refining process and the qualityof the end-products. The deterioration of bleachability index (DOBI) is a good indicatorof the capability of palm oil to be successfully refined. Beside commodities, especiallyrefined oils open a market for new high-quality products like golden palm oil, red palmoil, white soaps, fractionated products (CBE), etc. Optimization of the deodorizationtechnology and of the process conditions for a maximal retention of natural char-acteristics without affecting the quality of the palm oil is an important challenge.

Keywords: Chemical refining, physical refining, crude palm oil quality, DOBI, nutri-tional quality, carotenoids, tocopherols, tocotrienols.

Eur. J. Lipid Sci. Technol. 109 (2007) 315335 DOI 10.1002/ejlt.200600307 315

1 Introduction

The production of crude oils and fats, by normal opera-tions of rendering, crushing or solvent extraction, resultsin the incorporation of variable amounts of minor com-ponents like free fatty acids (FFA), partial acylglycerols,phosphatides, sterols, tocopherols, tocotrienols, hydro-carbons, pigments, vitamins, sterol glycosides, proteinfragments, traces of pesticides, dioxins, heavy metals,etc. Not all constituents are undesirable: tocopherols andtocotrienols, for example, perform the important functionof protecting oil against oxidation and possess vitamin Eactivity. The sterols, on the other hand, are colorless, heatstable and, for all practical purposes, inert; hence, theypass unnoticed unless present in unusually largeamounts. Unsaturated fatty acids (mainly the poly-unsaturated ones) are particularly sensitive to oxidation;this sensitivity is amplified by the presence of metal tra-ces like iron or copper which should be removed. Phos-phatides in the crude oil need to be removed becausethey will interfere within further processing.

To become acceptable for human consumption, mostoils must be purified. Mainly, a light color, a bland tasteand a good and oxidative stability are required. Toachieve this, the oils are submitted to several treatments.The objective of the refining is to remove the objection-

able minor constituents in the oil with the least possibledamage to the acylglycerols and minimal loss of thedesirable constituents.

2 Minor components of crude palm oil

As a fruit flesh oil, palm oil is produced at the oil mill bycooking, pressing and clarification. The quality of thecrude oil will affect the efficiency and yield of refining andthe quality of the fully processed product.

The minor components of palm oil have been reviewed byBerger [1]; beside triacylglycerols, the remaining compo-nents consist in a multitude of chemical entities, some ofthem having actual or potential commercial value.

2.1 FFA and partial acylglycerols

In over-ripe fruits or during harvesting, a very activelipase, most probably originating from yeast cells, will beresponsible for increased production of FFA and partialacylglycerols. While it is possible to obtain a crude palmoil with only 0.02% FFA from fresh ripe fruit, the acidity ofcommercial crude palm oils is on average about 3.5%.

The monoacylglycerol (MAG) content in crude palm oil isvery low (below 0.5%). Jacobsberg and Oh [2] reported atotal diacyglycerol (DAG) concentration in crude palm oilsranging from 5.3 to 7.7%. They also noticed no correlationbetween FFA, MAG and DAG contents: DAG found incrude palm oil is probably a residual by-product of the

Correspondence: Vronique Gibon, De Smet Technologies andServices, Da Vincilaan, 2 Bus G1, 1935 Zaventem, Belgium.Phone: 132 2 716 1111, Fax: 132 2 716 1109, e-mail: [email protected]

2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.ejlst.com

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316 V. Gibon et al. Eur. J. Lipid Sci. Technol. 109 (2007) 315335

biosynthesis of the TAG. These observations have beenconfirmed by Goh and Timms [3] who also reported asignificant correlation (based on a statistical study) be-tween MAG and DAG. More 1,3-DAG than 1,2-DAG iso-mers (in a proportion of about 2 : 1) are observed in allcrude oils.

2.2 Phosphatides and glycolipids

According to Goh et al. [4], the main phosphatide com-ponent in palm oil is phosphatidylcholine and the majorglycolipid is galactosyldiacylglycerol. On the other hand,Kulkarni et al. [5] have shown that Indian crude palm oilcontains (beside phosphatidycholine) phosphatidyletha-nolamine, phosphatidylinositol (more than 20% each)and, in lower quantities, phosphatidylglycerol. A detailedstudy of phosphatides in crude palm oil showed that mostof the phosphorus determined in the oil is in fact inorganicphosphate rather than from phospholipids. Typically, theinorganic phosphorus content is eight times that of thephospholipid phosphorus. Detailed studies of these twoforms of phosphorus compounds in crude palm oil indi-cate that they are unlikely to be the direct cause of someoil quality problems such as poor bleachability orincreased susceptibility to oxidation. The inorganic phos-phate presumably arises from the degradation of phos-phatides by phospholipases and further chemical trans-formation [6].

2.3 Tocopherols and tocotrienols

Characteristic of crude palm oil is its high content intocotrienols (mainly g-, a- and d-tocotrienols). g-Toco-pherol and a-tocopherol are the main tocopherols [1], withthe total content (tocopherols and tocotrienols) rangingfrom 600 to 1000 ppm [4]; the tocopherol/tocotrienol ratiois usually around 20%. Compared to other oils, palm oilhas a high proportion of tocopherols and tocotrienols inrelation to its unsaturation; the ratio tocopherols 1 toco-trienols (ppm) to polyunsaturated fatty acids (PUFA)(expressed in %) is about 50 (while it is only 19 for soy-bean and 12 for sunflower oils). Conjugated effects ofhigh tocopherols and tocotrienols and low PUFA couldexplain why palm oil would present a greater oxidativestability, for instance, in frying [1].

2.4 Carotenoids

As its deep red color testifies, crude palm oil is a richsource of carotenoid components (5002000 ppm). a-Carotene and mainly b-carotene are the main constitu-ents (about 90% of the total) [7]. Light-colored crude palm

oil demonstrates a low carotene content and suggestshigh oxidation of the crude oil. A spectrophotometricmethod is available to determine the carotene content ofpalm oil using n-hexane as solvent; the absorbance closeto 450 nm multiplied by an empirical factor 427 is fre-quently used to express carotene in ppm.

Carotenoids (and in particular b-carotene) are known fortheir pro-vitamin A activity and are strongly associatedwith the prevention of certain types of cancer [4]. Most ofthe carotenoids in palm oil are destroyed during therefining process, giving rise to light-colored products.Various methods of extraction and recovery of car-otenoids from crude palm oil are described, includingsaponification, adsorption, precipitation, solvent extrac-tion, molecular distillation and transesterification.

2.5 Sterols, methylsterols, triterpene andisoprenoid alcohols and hydrocarbons

The total sterol content in crude palm oil is around 500 ppm[7]. b-Sitosterol is the most abundant sterol (up to 60%).Campesterol, stigmasterol and cholesterol are observed inlower quantities. Sterols are observed as free or esterified(50 : 50) [1]; free and mainly acylated sterol glucosides arealso detected (up to 300 ppm). Methylsterols and tri-terpene alcohols are present at a concentration of800 ppm. Isoprenoid alcohol in crude palm oil is about80 ppm. Squalene, which is the major hydrocarbon incrude palm oil, ranges between 200 and 500 ppm; thecontent in non-terpene hydrocarbon is about 3050 ppm.Crude palm oil contains also 1080 ppm of ubiquinone-10and 5 ppm of ubiquinone-5, which are related to vitamin Kand have antioxidant properties [1].

3 Crude palm oil quality

Important aspects of the quality of the crude feedstockhave to be considered in that they affect the refining pro-cess (effect of ripeness, storage, transportation, etc.).Thechemical and physical properties of Malaysian crudepalm oil have been thoroughly determined from severalsurveys and the data have been incorporated in stand-ards (Tabs. 1 and 2) [8, 9].

3.1 FFA content

A powerful hydrolytic enzyme is present on the exterior ofthe palm fruits, and if it is not deactivated promptly afterharvesting, any oil escaping from damaged fruits or dur-ing processing splits rapidly into FFA and partialacylglycerols.


Eur. J. Lipid Sci. Technol. 109 (2007) 315335 Palm oil refining 317

Tab. 1. Quality requirements for crude palm oil (source:MS 814/1994) [8].

Characteristics Specialquality(SQ) grade

StandardqualityI

StandardqualityII

FFA (as palmitic) [% max] 2.5 3.5 5.0Moisture and impurities

[% max]0.25 0.25 0.25

Peroxide value [meq O2/kg max] 2.0 Anisidine value (max) 4.0 DOBI [min] 2.8 2.5 2.2

Tab. 2. Specifications for crude palm oil [9].

Specialgrade

Lotox Standard Contractual

FFA (as palmitic) [% max] 2.5 2.5 3.5 5.0Moisture [% max] 0.2 0.2 0.2 Basis pureImpurities [% max] 0.02 0.02 0.02 Basis purePeroxide value

[meq O2/kg max]3 3 5

Anisidine value (max) 4 3.5 Carotene [ppm max] 600700 Fe [ppm max] 4 4 5 Cu [ppm max] 0.02 0.2 0.2

Freshly expelled crude palm oil, promptly dried andcooled, will show low hydrolysis and oxidation. Crudepalm oil can be produced at less than 2.5% FFA and0.15% H20; at this moisture level, both hydrolysis andoxidation are slowed [10, 11]. An FFA content below3% gives some guarantee that fresh and unbruisedfruits were used and that the crude oil was stored andtransported under good conditions. Too high levels(together with high iron and copper picked up duringstorage and transportation) will lead to too high oxida-tion [12].

3.2 Phosphatide content

The phosphorus content of crude palm oil is quite vari-able, both in amount and in quality. Normally in the rangeof 1020 ppm, values less than 5 ppm have been reportedas well as values exceeding 30 ppm. As already men-tioned, only 1030% of this phosphorus occurs as phos-phatides; the major content being described as inorganic.The exact nature of this phosphorus component is stillunknown [4, 6].

3.3 Oxidation products and metal traces

Values as low as a peroxide value (PV) of 4 meq O2/kg, ananisidine value (AnV) of 4, iron of 3 ppm and copper of0.1 ppm are desirable in the crude oil. Whereas in 1970crude palm oil at a maximum content of 10 ppm iron and0.2 ppm copper was commonly offered, good crude palmoil at a maximum of 3 ppm iron and 0.02 ppm copper isavailable today. Copper is particularly unwanted asquantities below 0.02 ppm are capable of encouragingoxidative attack [13]: copper is considered as ten timesmore active as pro-oxidant than is iron. Contaminationwith trace metals mainly arises because of mechanicalwear and corrosion at the oil mill or during storage andtransportation; use of stainless steel can greatly reducethis level. Also, oil recovered from effluent treatment isparticularly rich in iron [9].

As specified before, crude palm oils of several grades arecommercially available, with the FFA content varying be-tween 2.8 and 5%. High FFA levels generally result in highiron and copper levels, picked up during transportationand storage, resulting in an acceleration of oxidation andan increase in Totox (two times PV 1 AnV) which cannotbe sufficiently reduced during refining.

Refiners using good-quality palm oil can easily fulfill therequirements of a good-quality refined oil based on FFA,iron, copper and color. But the Totox value seems to becritical: because transport conditions are governed moreby commercial requirements than by quality require-ments, this value can increase greatly during transporta-tion, obliging the European refiners to re-treat the alreadyprocessed oil.

3.4 Oxidized carotenoids

Good-quality crude palm oils of different origins showabsorption peaks in the region of 458 nm (UV spectros-copy) due to carotenoids. Modest deviations from a pre-cise absorption pattern are explicable by some variationin the carotenoids present in different species. If the crudeoil has suffered from damage, the height of the absorptionpeak is diminished and a displacement towards 450 nm isobserved [13]. Low-grade crude palm oils may sufferautoxidation of the carotenoids, giving rise to off-flavors.It is also shown that carotene has a pro-oxidant behaviorthat can overcome the positive effect of up to 0.1% oftocopherols and tocotrienols as scavengers of oxygen-free radicals [14].

Nitrogen blanketing of storage tanks during transporta-tion retards oxidation. Antioxidants can be added to thecrude oil (combination of TBHQ and citric acid), assuring



a better color of the oil after refining and allowing thereduction of bleaching earth consumption because theamount of oxidized crude oil has been substantiallyreduced [11].

3.5 Deterioration of bleachability index

The deterioration of bleachability index (DOBI) is a goodtest to assess the quality of a crude palm oil [15]. TheDOBI is basically the ratio between the content of car-otenes (measured at 446 nm) and secondary oxidationproducts (measured at 269 nm). Practically, the crude oilis dissolved in iso-octane or n-hexane and the absorb-ance at 269 nm and 446 nm is measured. It must be saidthat the DOBI is now recognized as an ISO method [ISO7932:2005].

DOBI Absorbance at 446 nmAbsorbance at 269 nm

An arbitrary scale has been suggested [13]:

DOBI 3.25 (very satisfactory quality); DOBI =62.75(average quality); DOBI ,2.0 (very poor oil).

However, other sources [16] propose less severe classifi-cations:

DOBI .2.3 (more easily refined); DOBI = 2.02.3 (unpre-dictable); DOBI ,2.0 (difficult to refine).

4 Refining practices for crude palm oil

Crude oils are refined to remove all impurities such asundesirable odor, flavor and color, but at the same timeretaining the beneficial components such as vitamins,pro-vitamins and antioxidants. Refining can be operatedaccording to two main routes: chemical refining or physi-cal refining. The principal difference between the tworoutes is how the FFA are removed. In a physical opera-tion, most FFA are removed in the deodorizing unit; oper-ating conditions (temperature, vacuum and steam) arecarefully selected in order to allow removal of the acids; awell-designed deodorizer operating at an acceptableefficiency will reduce the costs of the process. As distilla-tion requires a high-temperature treatment, the oil mustbe carefully degummed and bleached before entering thedeodorizing unit. At the opposite, if the chemical refiningoption is chosen, the oil is cleared from gums and FFAduring the alkali neutralization step and soapstocks areproduced. More than 95% of crude palm oil in Malaysia isrefined through the physical route [refined, bleached anddeodorized (RBD) palm oil].

The physical refining process can offer important advan-tages to the refiner, such as higher oil yield, reduction of

the use of chemicals (like phosphoric acid, sulfuric acidand caustic soda), reduction of water and effluent, andhence considerable reduction of the environmentalimpact [17, 18]. Unfortunately, bleaching earth consump-tion will be higher.

The final choice between chemical and physical refiningwill depend on a number of factors: the quality and theacidity of the crude oil, the ability to get rid of the soap-stock, and local environment legislation. Although physi-cal refining can be applied to almost any quality of crudeoil, the process more depends on the crude oil qualitythan chemical refining. This can be explained by the factthat a wide range of undesirable products is much moreeasily removed by alkali neutralization than by degum-ming.

For crude palm oil with low phosphatides, high initial FFA(up to 5%) and high carotene content, physical refining ispreferred in terms of operating costs and refining losses;deodorization at reduced temperature and improvedvacuum are an alternative when retention of minor com-ponents like tocopherols and tocotrienols is important.

Chemical refining is still used at a limited capacity [neu-tralized, bleached and deodorized (NBD) palm oil]. Crudepalm oil is mixed with citric or phosphoric acid for easyremoval of gums prior to neutralization of the FFA. Neu-tralized oil is separated from the soapstock by cen-trifugation; the neutralized oil is then washed with warmwater to reduce the residual soaps and dried undervacuum, before proceeding to bleaching and deodoriza-tion.

5 Physical refining practices

5.1 Degumming

Water degumming is the simplest method for phospha-tide reduction. However, mainly the hydratable phospha-tides [phosphatidyl choline (PC) and phosphatidyl inositol(PI)] can be removed by mixing the oil just with water.

Oils with a low content in phosphatides can be degum-med straight according to a wet acid degumming tech-nique. The hot crude oil (8090 7C) is thoroughly mixedwith phosphoric or citric acid, followed by a retention timeof approximately 520 min; then 25% water is mixedwith the oil before going to a centrifugal separation. Infact, one common property of phospholipids is that theyform hydrates in contact with water, and these hydratesare insoluble in oil. The rate of hydration of phospholipidsvaries substantially at 80 7C. PC and PI hydrate very fastwhile phosphatidic acid (PA) and phosphatidyl ethanola-mine (PE) (mainly present as calcium and/or magnesium



salts) react considerably more slowly with water. The PChydrate is not only rapidly formed but it can also encap-sulate PA 1 PE 1 PI at about 80% of its own weight [19].This means that when the phospholipids in the crude oilcontain about 55% PC, they all can be removed by fasthydration at elevated temperature. If the phospholipidscontain only about 3035% PC, fast hydration will giveonly partial removal of the slowly hydrating phospholip-ids. An acceleration of the rates of hydration of the cal-cium and magnesium salts of PA and PE can be obtainedby addition of a strong acid prior to hydration. Thisexplains the varied performance of wet acid degummingaccording to the composition of the gums. Wet aciddegumming is mainly used for crude palm oils with highphosphatide and iron contents.

Soft degumming [20] is another option to remove phos-phatides from crude palm oil with high phosphatide andiron contents. In this case, the oil is heated (7585 7C) andmixed with a water solution (2%) containing a complexingmolecule [ethylene diamine tetracetic acid (EDTA)] and,eventually, a wetting compound [sodium dodecyl sulfate(SDS)]. EDTA is able to form strong chelates with magne-sium, calcium and iron. As a consequence, non hydrat-able phospholipids will be more easily removed. After20 min of retention time followed by centrifugation, lessthan 1 ppm of phosphorus can be achieved. Iron isreduced to below 0.1 ppm as it forms an oil-insolublecomplex with EDTA.

For palm oil, dry degumming is the most common way.Classically, crude palm oil is first mixed with about 0.050.1% concentrated phosphoric acid; after a short reten-tion time, about 1 or 2% acid-activated bleaching earth isadded under vacuum at a temperature of 80120 7C. Aftera suitable contact time, the spent earth is removed by fil-tration. The phosphoric acid disrupts non-hydratablephosphatides by decomposing magnesium and calciumcomplexes; it coagulates the phosphatides, sequestratesiron and copper, before being removed by adsorption onbleaching earth. Sometimes citric acid is also used, butdue to economical reasons, phosphoric acid is mainlyused by Malaysian refiners. The amount of acid intro-duced into the oil is quite critical: under- or over-dosagemay lead to darkening of the oil during deodorization.Phosphatides (due to low acid dosage) break down at thedeodorization temperature, leading to darkening and off-flavor problems [13]. An excess of phosphoric acid (over-dosage) also promotes darkening of the RBD palm oil[21].

When using concentrated phosphoric acid with 85%strength (commonly 0.050.1%), there is a danger topromote phosphorylation of some triacylglycerols (lipo-philic phosphorus) [13, 16]. Sometimes, calcium carbon-

ate is added to neutralize any remaining phosphoric acidbefore filtering, but this is not good since non-hydratablecalcium phosphatides are formed, leading to less satis-factory phosphorus removal [22]; when strong phosphor-ic acid is used (85%), iron removal seems to be more dif-ficult [23]. These problems can be avoided by using citricacid (0.05 wt-% dose of citric acid as a 30 or 50% solu-tion in water), a mixture of phosphoric and citric acids(2 : 1), or a diluted phosphoric acid solution (.50%).

Adsorptive cleansing should reduce the phosphorus levelto an acceptable limit (below 2 ppm), lower the tracemetal content (Fe ,0.1 ppm) and minimize oxidationproducts. The color of palm oil after earth bleaching aloneseems to be not important as carotenoids are known tobe efficiently thermally bleached under the conditions ofdeodorization. After 20 min at 180 7C, half the carotenehas disappeared, at 200 7C about 70%, and at 240 7Cmore than 98% [24, 25].

At a certain moment, the question was raised as towhether the thermal bleaching and deodorization of palmoil at temperatures around 270 7C for a few minutes or at220240 7C for longer times give rise to polycyclic aro-matic hydrocarbons from the carotenoid pigments; it isnow clear that this effect should be negligible [4, 26].

5.2 Bleaching

Adsorptive bleaching is an integral part of the process ofrefining edible oils and can only exceptionally be omittedif the oil to be refined is very low in components requiringremoval.

5.2.1 Principle

The removal of minor components through adsorptivebleaching is based on several adsorption mechanisms.Part of the coloring pigments (carotenoids in the case ofpalm oil) are physically adsorbed on the bleaching clays,involving Van der Waals surface attraction forces. Othercomponents are chemically bound to the bleaching claysurface via covalent or ionic bonds. Part of the impuritiesis removed through molecular entrapment in the porousstructure of the clays. During bleaching, some minorcomponents are chemically altered due to the catalyticactivity of the clays: a typical example is the decomposi-tion of the hydroperoxides into unsaturated conjugatedproducts.

The most important factors affecting absorptive bleach-ing are temperature and humidity, but the structure (par-ticle size distribution) and the type of bleaching earth[heat- (neutral) or acid-activated] also play a crucial role.



Neutral bleaching clays are aluminum silicates whichcontain relatively high amounts of calcium, magnesium oriron. These clays are normally activated through heattreatment; the high metal content limits the adsorptiveactivity of these clays. The metals can be removed fromthe reactive spots by means of an acid treatment, result-ing in acid-activated clays with a much higher adsorptivecapacity. It is generally assumed that the spent filter cakecontains about 2030 wt-% oil, but is has been proved[27] that the amount of neutral oil losses when disposingof the cakes is considerably higher than generally recog-nized (above 45%).

5.2.2 Bleaching process

The bleaching process is by far the most expensive pro-cess in refining when considering the utility costs. Therelatively high cost of the bleaching clays as well as theoil-in-earth losses and bleaching adsorbent disposalcosts largely affect the operating cost of a bleachingplant.

The strong environmental regulations are also forcing allrefiners to reduce as much as possible the solid wastestreams as they are difficult to treat. Several bleachingprocesses have been developed over the years to reducethe bleaching earth consumption.

Bleaching is performed in several stages:

Prior to bleaching, the oil is properly deaerated and driedunder reduced pressure (,100 mbar) to a moisture con-tent of 0.1%. Deaerated bleaching earth is added to theoil under controlled conditions of temperature, acidity andhumidity for a specific residence time (2030 min). Thebleaching clay is dosed directly to the oil or in a slurryform (pre-mix of oil with bleaching earth). It is of greatimportance that both oil and bleaching earth are free fromoxygen before mixing, to avoid oxidation and hencedeterioration of the oil. The oil is further heated underreduced pressure and intensively mixed, sometimes byinjection of steam to ensure intimate contact between thebleaching earth and the oil. Finally, the mixture is trans-ferred to a filter, usually a hermetic leaf filter (horizontal orvertical) with stainless-steel mesh elements, followed bypolishing filtration. The first oil that passes through theleaf filter is normally recycled back to the bleacher vesselas it may still contain too much bleaching earth. Thebleached oil is afterwards diverted to the bleached oilstorage tanks and kept under nitrogen. Bleaching filtra-tion is sometimes improved with a pre-coat of diatomac-eous earth. The spent bleaching earth cake is blown bysteam or nitrogen to recover as much as possible theentrained oil from the cake.

5.2.3 Single-step bleaching

The oldest method of bleaching, which is still followed invarious bleaching plants, is the batch bleaching where alloperations are executed in the same vessel (except forthe filtration).

Continuous vacuum bleaching protects the oil from oxi-dation since deaeration is more efficient. The total holdingtime of the oil is much shorter, which minimizes the risk ofunwanted side reactions such as conversion of soaps intoFFA in the case of acid bleaching earth. Another benefit ofcontinuous bleaching is the energy savings that can beobtained by heat recovery. In the case of dry degummingof crude palm oil, there is no separate degumming step;the acid-activated phosphatides are adsorbed on thebleaching clay and as such removed from the oil (Fig. 1).

5.2.4 Multi-step bleaching

In order to reduce bleaching earth consumption, alter-native multi-step bleaching processes have been devel-oped.

The most known are the two-stage co-current and coun-ter-current bleaching processes.

The co-current process is the least complicated and lessperforming two-stage process: bleaching earth is addedin two consecutive stages to the oil, with a filtration afterevery stage. The counter-current bleaching process is themost efficient (Fig. 2). In this process, the spent bleachedearth from the second bleaching stage is re-used in thefirst stage. The efficiency of the counter-current processis largely affected by the way the filtration with spentbleaching clay is performed. The easiest way is to use athird filter operating in counter-current at the inlet of thebleacher. The pre-filtration of the oil through the spentbleaching clay cakes in the filter, built up during the sec-ond bleaching stage, already results in a saving of 1015% bleaching earth as compared to conventional single-stage bleaching. The main function of pre-filtration is toremove all solid impurities as well as to absorb most ofthe phosphatides and soaps. This allows a more efficientbleaching in the second stage. Even more efficient thanthe counter-current pre-filtration process is the Oehmiprocess [28] which guarantees savings up to 40%. Thisprocess features two bleachers and two sets of filters(Fig. 3). The spent bleaching clay of the second filtration ismixed back into the degummed oil in a specific mannerand subsequently filtered. It is interesting to note that over60% of the undesirable substances are removed in thefirst process stage.



Fig. 1. Classical single-stage bleaching (continuous vacuum bleaching with acid pre-treatment) [17].

Fig. 2. Two-stage counter-current bleaching with pre-filtration.

For palm oil, bleaching earth consumption has beenquantified with conventional single-stage and counter-current processes [17]. A bleaching earth consumption of1% can be reduced to 0.8% with a conventional pre-fil-tration, and up to 0.6% with the full counter-current sys-tem.

Recently, a multi-stage modular bleaching system(Combiclean) has been developed [29]. Basically, itcombines silica pre-treatment, pre-filtration with spentbleaching clays, bleaching, and eventually activated-car-bon post-treatment (Fig. 4). Savings of up to 30% arereported. Pre-treatment with silica is particularly interest-



Fig. 3. Two-stage counter-current bleaching according tothe Oehmi principle. (1) Bleacher 1 (pre-bleaching),(2) pump, (3) pump, (4) bleacher 2 (final bleaching),(5) mixer, (6) bleaching earth doser, and (7) filter [32].

ing to selectively remove phosphatides and soaps if cer-tain unwanted minor components have to be considered.In some cases, active carbon is applied to take out non-volatile contaminants such as high-molecular-weightpolycyclic aromatic hydrocarbons or dioxins. Active car-bon is added together with bleaching earths or mixed withthe bleached oil after bleaching. Full separation ofbleaching clays and active carbon is preferred as it resultsin two separated waste streams: non-toxic spent bleach-

ing earth and potentially toxic spent activated carbon.Such separation may be important for further utilization ordisposal. On top of that, active-carbon consumption isreduced by 50%.

5.2.5 Packed (fixed)-bed bleaching

Packed- (or fixed-) bed bleaching is used in some re-fineries; it refers to pre-loading all or some of the bleach-ing earth on a filter and pressing the oil through thepacked-bed instead of continuously mixing all the earthwith oil [13]. This ensures the optimum use of the bleach-ing earth by pre-coating it onto a filter in the form of ashort, wide chromatography column [27]. Silica adsor-bents are mainly used in combination with bleachingearth to prevent blocking of the oil flow due to soaps andphosphatides; in this case, the filter cake consists of twolayers: a first layer with silica and a second layer withbleaching earths. Residual bleaching capacity is con-tinuously monitored by on-line measurement of a specificcomponent; when this capacity has been reached, thefilter is cleaned in the normal way and re-coated.

5.2.6 Wet and dry bleaching

Continuous bleaching units are often operating by meansof the wet bleaching concept. With wet bleaching, theremoval is more effective and the consumption ofbleaching earths can be reduced. It is known that duringbleaching, soaps are converted into FFA due to the acidic

Fig. 4. Multi-stage modular bleaching (Combiclean) [29].



properties of the bleaching earth. Another side reactionthat can occur during bleaching, in case the oils are notsufficiently dried or the earths are still too wet, is thehydrolysis of TAG that will increase the DAG and FFAcontents [30]. The second side reaction can be avoidedby simply drying the oil before bleaching and assuringthat the bleaching earths are not too wet. Nevertheless, itcan be desirable that the oil contains sufficient amount ofwater when bleaching earth is added. During the so-called wet bleaching [31], non-hydratable phosphatidesare hydrated in the presence of chelating acids and water;the presence of water will increase the cation exchangecapacity of the bleaching earth. The best performance isobserved for an amount of water of about 50100% of theamount of bleaching earth, which is not always econom-ically acceptable. In wet bleaching, the materials areallowed to come into contact with each other under at-mospheric pressure for 20 min at about 7090 7C. This isfollowed by the usual bleaching process under vacuumfor 1530 min. During this step, the excess water evapo-rates so that the bleaching earth can be filtered withoutproblems.

Certain silica gels with a water content of 6070% canalso be used instead of wet bleaching to remove phos-phatides. Compared to the normal bleaching earths,these materials have a much higher adsorption capacityfor phosphatides, soaps and metal traces and can par-tially replace the bleaching earths. However, pigments(chlorophyll, carotenoids) are weakly adsorbed by thesesilical gels [32].

5.2.7 Residual phosphorus content afterbleaching

After bleaching, the oil should be almost free from phos-phorus, iron and copper.

According to Zschau [32], the efficiency of phosphorusremoval in dry degumming of palm oil depends on theconditions chosen; temperatures below 120 7C and acti-vation of phosphatides with diluted phosphoric acid orwith citric acid are preferred (Tab. 3). If instead of phos-phoric or citric acid, pure water (up to 1.5%) is added atthe same time as the clays at atmospheric pressure (wetbleaching), phosphorus removal is very efficient; the datacorrelate with the quantity of water (Tab. 4) [32]. Indeed,the clays have also acidic properties and ion exchangecapacity and could take the role of phosphoric and citricacids. When quite concentrated phosphoric acid is used(.75%), there is a critical relationship between the acidand bleaching earth dosages and the residual phos-phorus content (Tab. 5) [33].

Tab. 3. Influence of temperature and acid (concentrationand type) on residual phosphorus content (ppm) ofbleached palm oil$ [32].

Temperature[7C]

0.15% Phosphoricacid (85%solution)

0.15% Phosphoricacid (10%solution)

1.5% Citricacid (10%solution)

90 9.8 3.3 1.7120 21.1 3.6 1.3150 38.8 3.7 3.4

$ Crude palm oil: P: 9.9 ppm; FFA: 5.6% (as palmitic).Bleaching earth: 1.5% Tonsil Supreme FF.Calcium carbonate used after phosphoric acid treatment.

Tab. 4. Influence of added water and temperature onresidual phosphorus content (ppm) of bleached palm oil$

[32].

Temperature[7C]

0%Water

0.5%Water

1.0%Water

1.5%Water

120 8.5 5.3 3.2 2.7135 6.8 4.5 3.0 2.9150 6.6 4.0 2.5 3.2

$ Crude palm oil: P: 17.1 ppm.Bleaching earth: Tonsil Supreme FF.

5.2.8 Adsorption of pigments

In the physical refining of crude palm oil, full reduction ofcarotene by bleaching is not necessary as carotenoidsare mainly decomposed by heat during deacidification(heat bleaching; see Section 5.1).

When palm oil is to be used for biodiesel production, thecolor is of minor importance; removal of phosphatides isthen the most critical aspect of the pre-treatment; in thiscase, the addition of bleaching earth might not be neces-sary and simple acid washing or soft degumming is asuitable alternative option (Tab. 6) [33].

Rossi et al. [34] have studied the effect of bleaching on thecolor of degummed palm oil. Five concentrations of oneneutral and two acid-activated bleaching clays mixedwith a fixed amount of synthetic silica were used forbleaching (110 7C, 20 min under vacuum) after aciddegumming. Neutral bleaching clays seem to be lessefficient than acid-activated clays to remove carotenoids(Tab. 7). For the activated clays, pigment removal clearlyincreases with the amount.



Tab. 5. Influence of acid dosage on dry degumming effi-ciency of crude palm oil [33].

0.07% Phosphoric acid (75%); 1% Tyco Classic bleaching earth

Crude palm oil Degummed palm oil

FFA (as palmitic) [%] 5.68 P [ppm] 17.5 4.6Fe [ppm] 7.5 0.1Ca [ppm] 18.2 0.2Mg [ppm] 4.9 0.1









FFA (as palmitic) [%] 4.38 P [ppm] 17.1 not detectedFe [ppm] 6.2 0.1Ca [ppm] 14.0 0.2Mg [ppm] 4.5 0.1

Tab. 6. Influence of several pre-treatments on residualphosphorus content of crude palm oil [33].

Pre-treatment Residual P Residual Fe

Water washing$ 13 10Acid water washing$ 6 4Soft degumming 2.5 0.5Acid conditioning followed by

partial caustic treatment andwater washing$

7.5 1

$ Crude palm oil: FFA: 4.8%; P: 16.0 ppm; Fe: 13.0 ppm. Crude palm oil: FFA: 4.8%; P: 13.7 ppm; Fe: 3.8 ppm.

5.2.9 Catalytic properties of bleaching earths

Some reactions observed during bleaching can be clearlyattributed to the catalytic properties of the clays. Themost important one is the decomposition of hydroper

Tab. 7. Influence of degumming and bleaching earthquality and quantity on carotenoid retention (ppm) in palmoil (bleaching conditions: 110 7C, 50 mbar, 20 min;0.125% synthetic silica added to the bleaching clays)[34].

Treatment Carotenoids[ppm]

Crude palm oil 455.8Acid-degummed palm oil 415.0

Bleached with acid-activated clay 1:0.5% bleaching clay 1 297.00.75% bleaching clay 1 245.81.0% bleaching clay 1 223.4

Bleached with acid-activated clay 2:0.5% bleaching clay 2 327.90.75% bleaching clay 2 313.91.0% bleaching clay 2 258.6

Bleached with neutral clay:0.5% neutral clay 324.40.75% neutral clay 329.91.0% neutral clay 304.0

oxides; while PV decrease rapidly during bleaching, AnVonly decline. This leads to the reasonable deduction thatthe catalytic decomposition of peroxides is preferred overthe adsorption of aldehydes and ketones on the activesite of the clays [13]. It is described that oils refined usingacid-activated earth during bleaching have a better finalacidity and oxidative stability than oils refined using non-acid-activated earth [35]. It has also been reported thatrefined oil bleached with low-quality clay exhibits lessstability in color, FFA and peroxides [30].

Conjugated dienes and trienes are formed during bleach-ing of palm oil as a result of the decomposition of hydro-peroxides [36]. For a given oil, the amount of conjugateddienes, measurable at 233 nm, is related to the bleachingearth dosage; bleaching earth below 1% seems to allowless formation of conjugated dienes. An increase of con-jugated trienes during bleaching depends on the crudepalm oil quality, independently of the bleaching earthused. Some of these conjugated trienes can be removedlater during deodorization. Low conjugated dienes andtrienes in the refined oil are an indicator of mild refiningconditions and good-quality crude oil.

5.2.10 Irradiation bleaching

Recently, irradiation bleaching has been described [37]on red palm oil, palm olein and palm stearin. The bleach-ing level achieved by irradiation is comparable to the



bleaching achieved by heating. The general quality of theresulting oils is better if they are bleached with irradiation,as the amount of the polar fraction resulting from irradia-tion is minimal relative to that found in heat-treated oil.The conclusion is that infrared bleaching is economicallymore viable than solar irradiation techniques and heatbleaching, as it can be performed easily with no oil lossesand less energy consumption.

5.3 Deodorization

5.3.1 Process parameters and conditions

Deodorization is basically a vacuum steam stripping atelevated temperature, during which FFA and volatile odi-ferous components are removed to obtain a bland andodorless oil. Although the process is commonly nameddeodorization, it is actually a combination of three dif-ferent operations: (a) distillation, i.e. stripping of volatilecomponents (FFA, tocopherols, tocotrienols, sterols andcontaminants like pesticides or light polycyclic aromatichydrocarbons, etc.); (b) actual deodorization, i.e. removalof odoriferous components; and (c) heating effect, i.e.thermal destruction of pigments (carotenoids) whilemaintaining low side reactions such as cis-trans iso-merization, polymerization, etc.

Optimal deodorizing parameters (temperature, operatingpressure and amount of stripping gas) are determined bythe type of oil and the selected refining process (chemicalor physical refining), but also by the deodorizer design.Physical refining requires more severe conditions thanchemical refining. This is mainly because of the distillativeremoval of the FFA, which is more critical in physicalrefining as the initial FFA levels are considerably higher.

5.3.2 Theory

The stripping medium requirements are described by thefollowing mathematical equation derived from Daltonsand Raoults laws.

SO Pt

E:P0i:ln

VaV0

PtE:P0i

1 !

:Va Vo (1)

whereby S = total moles of steam; O = total moles of oil; Pt= total pressure; Pi

o = vapor pressure of a given fattyacid i; E = vaporization efficiency; Va = initial molar con-centration of the volatile component in the oil; and V0 =final molar concentration of the volatile component in theoil.

When the initial FFA content is low, as in the case of aclassical deodorization, (Va V0) becomes so small thatEq. (1) can be simplified to:

SO Pt

E:P0i: ln

VaV0

(2)

In the case of physical refining, the partial pressure of thefatty acids cannot be neglected, and omitting the term(Va V0) would lead to a considerable underestimation ofthe stripping medium requirements.

This simplified Eq. (2) is also known as the Bailey Equa-tion. It states that the amount of steam required for deo-dorization or physical deacidification is directly propor-tional to the amount of oil and the absolute pressure in thedeodorizer and inversely proportional to the vapor pres-sure of the pure volatile component at the process tem-perature and the overall vaporization efficiency E.

The last factor in Eq. (2) (ln Va/V0) indicates that it isimpossible to eliminate all volatile components from theoil, since this would require an infinite amount of strippingmedium.

5.3.3 Deodorizer systems

Deodorization can be conducted in different ways (batch,semi-continuous and continuous) [38]. The selection ofthe most appropriate deodorizer technology depends onmany factors, such as the oil quality requirements, thenumber of feedstock changes, heat recovery, investmentand operating costs.

Batch deodorization is especially suitable for small ca-pacities, irregular production, or in processing smallbatches of different oils. Semi-continuous deodorizersare basically batch operating systems designed for largercapacities. In most designs, a batch of oil is transferredinto the system and then sent by gravity in a timesequence through a number of vertically stacked com-partments or trays.

Continuous deodorizers are most preferred by high-ca-pacity plants with few stock changes. The main advan-tages are the moderate investment costs, the possiblehigh heat recovery and the easy maintenance. Verticaltray-type deodorizers are probably the most used type ofcontinuous deodorizers (Fig. 5). Their design is based ona series of trays or compartments stacked vertically in acylindrical shell, with each tray designed for a specifictask.

All operations, heating, deodorization and heat recovery,are combined in a single vessel. All different deodorizerdesigns attempt to provide the best contact between the



Fig. 5. Continuous vertical deodorizer (De Smet) [38].

gas phase and the oil phase by creating large contactsurfaces and/or thin oil films together with an optimalsparge steam distribution (for an optimum level of vapor-ization efficiency). The sparge steam is introduced intothe oil through special distributors, which can be spargecoils with very fine holes (between 0.5 and 2.5 mm) (shal-low-bed deodorizer) or even sintered metal pipes (deep-bed deodorizers). Steam lift pumps have been introducedin order to improve agitation and overall deodorizationefficiency by continuously refreshing the oil in the toplayer [38]. The vapors from the different compartmentsare collected in a central chimney and sent to a separatevapor scrubber with a sprayer system. In some cases, anextra structured packing is installed in the scrubber toimprove condensation and to reduce fatty matter carry-over to the barometric water condenser system.

Due to the new market demands for minimizing transfatty acid and tocopherol and tocotrienol retention, adual-temperature concept has been recently developed.In the first tray, the incoming oil is heated to moderatetemperature, after which it passes through the first deo-dorization trays. In these trays, deacidification and deo-dorization take place under mild conditions (moderatetemperature/moderate stripping). After the first trays, theoil passes a second heating tray in which the oil is heatedto a final and higher temperature. In the last tray, finalstripping and heat bleaching occur. The process param-eters can be adjusted to arrive at the desired tocopheroland tocotrienol level in the refined oil. In general, the dual-temperature deodorizer shows a number of benefits thatare important for oil refiners. The benefits include lowtrans fatty acid formation because the time at hightemperature is restricted, maximum heat bleachingeffect, and adjustable tocopherol and tocotrienolremoval, mainly by steam injection at high temperature.

Packed columns (Fig. 6) are more and more used in edibleoil deodorization. A packed column is basically a single-shell vertical vessel in which a structured packing isinstalled. In fact, in the past, a structured packing wasoften installed to increase the capacity of existing deo-dorizers. Its main function was to reduce the spargesteam consumption of the deodorizing unit by pre-strip-ping the main part of the volatile material. The deacidifiedoil is then sent to the deodorizer for the final deodoriza-tion. In palm oil deodorization, for example, the FFA levelis first reduced from 35% to below 0.5% in a structuredpacking before the oil enters the deodorizer. In this way,the capacity of a deodorizing plant can be significantlyincreased. The main advantages of the structured packedcolumn are the higher efficiency to remove FFA and theshort residence time (only a few minutes).

Recently, a fully modular single-vessel (continuous)stand-alone deodorizer was designed (Qualistock) (Fig. 7)which requires no building and minimal piping. In this way,the erection costs can be significantly reduced. This con-cept allows the integration of different processing optionswith specific functions to improve the overall quality of thedeodorized oil: dual-temperature treatment, deep- orshallow-bed deodorization, packed column pre-strip-ping, dual condensation, etc.

5.3.4 Dry (or ice) condensing systems

Normal deodorizers operate at 34 mbar. Today, specialvacuum production units have been developed to reachlower pressures (,2 mbar) and better operating costsand, at the same time, to reduce emissions and effluentsby a more efficient condensation of the volatiles. The drycondensing system [38] is becoming more and more the



Fig. 6. Packed column stripper (Alfa-Laval) [38].

Fig. 7. Modular single-vessel stand-alone deodorizer (Qualistock-De Smet) [38].

standard in new refining plants. In this system, the vaporis condensed on surface condensers working alternatelyat very low temperature (around 30 7C). The remainingnon-condensables are removed either by mechanicalpumps or roots blowers in series with a liquid ring pumpor by a vacuum steam ejector system (booster). The dry

condensing system significantly reduces the motivesteam consumption, but requires extra electrical energy.

The commercially available dry condensing systemsconsist of two or more condensers, with either horizon-tally or vertically orientated straight tubes, a refrigeration



plant for the generation of cold refrigerant (usually NH3)which is evaporated in the tubes, and a vessel with rela-tively warm water for defrosting and cleaning of the tubesafter a certain period of freezing. A new dry condensingsystem has recently been developed [38]; the mostessential feature of this system (Sublimax) (Fig. 8) is thevertical orientation of the freeze condensers, combinedwith individual refrigerant injection in the tubes andsparge steam inlet at the top.

5.3.5 Side effects of deodorization

Possible changes that may occur on the chemical andphysical properties of palm oil and palm fractions underdifferent refining conditions have been described. In thecase of palm olein and palm mid fraction, trans fattyacids are mainly formed at 280 7C after a residence timeof 4 h (2.1 and 1.5%, respectively) [36]. In commercialrefined palm oil products, not more than 0.6% of totaltrans fatty acids are reported for processing conditionsof 260275 7C and a residence time of 4590 min.

Intra-molecular rearrangements of fatty acids can beobserved in oils subjected to drastic refining conditions(above 270 7C for long residence times); intra-esterifica-tion may occur during deodorization of palm oil, resultingin an increase in saturated fatty acids at the 2-position ofthe TAG. This intra-esterification has a detrimental effecton the efficiency of dry fractionation of palm oil and on thequality of the final fractions.

Removing FFA and partial acylglycerols (mainly MAG) willalso change the physical properties of palm oil; mainly thesolid fat content at low temperature will be affected(increased in the refined palm oil).

6 Chemical refining practices

In the case of chemical refining, the non-hydratablephosphatides which remain in the oil after acid treatmentare further removed during the neutralization stage. It isassumed that caustic soda converts the non-hydratablephosphatides into sodium salts, which are more easilyremoved as they are less oil soluble. On the other side,both calcium hydroxide and magnesium hydroxide arestrong bases and therefore do not replace easily theequally strong base sodium hydroxide. In this context, it isknown [39] that the pH must be very high for the residualphosphorus to be ,5 ppm.

The high soap content in combination with intense waterwashing improves the removal of the phosphatides. Theonly drawback is the soapstock which needs to be treat-ed accordingly.

The long mix technique (American route) was developedbased on a long time/low temperature sequence. Histori-cally, it has been especially designed to treat fresh NorthAmerican soybean oil. On the other hand, the short mixtechnique (European route) consists in a short contacttime at higher temperature.

Fig. 8. Schematic diagram of the improved Sublimax Dry Condensing system [38].



6.1 Typical process conditions

The non-hydratable phosphatides are removed by add-ing 0.030.1 wt-% of concentrated phosphoric acid tothe crude palm oil. The quantity of caustic solution iscalculated based on the FFA content of the oil; in ashort mix process, 20227 B caustic soda (1030%excess) is generally used and mixed to the oil at 9095 7C in order to avoid emulsion formation. The contacttime is generally 30 s to prevent high saponificationlosses. The soapstock/oil mixture is delivered toseparators. The outgoing light phase is the neutralizedoil containing traces of soaps, free caustic, phospha-tides and other soluble impurities. The neutral oil lossesshould be usually between 20 and 30%. Soft water atabout 90 7C is added to the oil for washing and sepa-rated in a second centrifuge into water-washed oil aslight phase and soapy water as heavy phase. The rangeof the FFA content in neutralized oil is usually between0.08 and 0.25%, and the soap content is below50 ppm. After drying, the neutralized oil is sent forbleaching and deodorization (220240 7C) to removemainly odoriferous components and to bring the finalacidity into the range of 0.020.08%.

6.2 Soapstock splitting

Soapstock splitting is closely connected with causticrefining and is completely omitted in physical refiningplant facilities. Soapstock from alkali refining is pumpedto the splitting plant for acid oil production. The totalfatty matter of diluted soapstock is usually around 1015%. Sulfuric acid is mixed and the reaction takes placein a decantation tank, to break down the emulsionformed due to the presence of phosphatides, proteinsand other mucilaginous substances. Acid water isremoved, leaving acid oil to pass through a separator,allowing the removal of last traces of water and mucila-ginous material. Extra washing is performed to assurethat no sulfuric acid is left in the acid oil. Soap splitting isgenerally done at pH ,3. The FFA content of the acid oilproduced is usually between 40 and 70%, depending onthe quality of the soapstock used and more especiallythe amount of neutral oil in the soapstock. The maincomponents of palm acid oil are FFA, neutral oil andmoisture. It is mainly used for making laundry soaps andfor producing calcium soaps for animal feed formula-tions.

Properties (quality and oxidative parameters) of palmoil acid oil have been carefully analyzed in order tobuild up specifications and a clear definition of palmfatty acids (Tab. 8) [40]; moisture, FFA, PV, iodine

Tab. 8. Quality and oxidative parameters of palm acid oil(mean of 27 samples) [40].

Parameter Meanvalue

Standarddeviation

Moisture content [%] 0.98 0.53Free fatty acids [%] 62.6 11.5Peroxide value [meq O2/kg] 4.1 3.8Iodine value 50.2 5.3Saponification value 186 5.6Unsaponifiable matter [%] 0.53 0.42

value, saponification value and unsaponifiable matterhave been quantified. A few samples showed the pres-ence of aldehydes, ketones, furans and volatile acids.

7 Deodorizer distillate

7.1 Composition of deodorizer distillate

The composition of the deodorizer distillate is not only oildependent, but it is also determined by the refining tech-nique applied (physical or chemical) and the operatingconditions during deodorization [17, 18] (Tab. 9). In thecase of physical refining of palm oil, the distillate mainlyconsist of FFA (8388%) with only small amounts of unsa-ponifiable components (24%) and neutral oil (813%).Deodorizer distillate is generally sold as a source of indus-trial fatty acids or eventually for soap production in somecases after deodorizing to reduce the color. It can also beconsidered as a feedstock for biodiesel production.

Tab. 9. Typical composition (%) of a deodorizer distillatefrom a chemical and a physical refining plant [18].

Composition Chemicalrefining

Physicalrefining

Neutral oil 2533 510Fatty acids 3350 8085Unsaponifiable matter (including

tocopherols and sterols)2533 510

7.2 Neutral oil losses during deodorization

Neutral oil losses during deodorization generally dependon the oil composition and deodorizing conditions [38]. Inthe case of chemical refining, improvement of the deo-dorizer design has significantly reduced entrainment los-ses to 0.10.2%. For physical refining of palm oil, addi-tional loss directly proportional to the FFA content andmainly due to mechanical carryover has to be taken into



account. Higher MAG contents of high acidity oils alsocontribute to losses. In practice, there is also limitedhydrolysis during deodorization; under normally applieddeodorizing conditions, hydrolysis results in the produc-tion of 0.0150.020% additional FFA [41].

7.3 Dual condensing system or washing section

The FFA content of palm deodorizer distillate is usuallyaround 8590%. With the introduction of a dualcondensing system [33], in some designs also calledwashing section [42], the content of acylglycerols (MAG,DAG and TAG), tocopherols, sterols, squalene, etc., in thecondensed fatty acids can be reduced. The compositionof palm oil distillate without and with this system is pre-sented in Tab. 10; the total amount of FFA is increased to98% min.

Tab. 10. Composition (%) of palm fatty acid distillateincluding or not a washing section [42].

Components Without washingsection

With washingsection

FFA 87.4 98.1MAG 2.0 0.7DAG 0.7 0.05TAG 8.0 0.1Tocopherols, sterols,

squalene1.9 1.0

8 Special products

8.1 Golden palm oil

A golden palm oil rich in carotene, tocopherols and toco-trienols can be obtained by physical refining.

The characteristics of a high-vitaminic physically refinedpalm oil (produced under pilot conditions) have beendescribed [43]. It has been claimed that this golden oilshould retain 20% of the initial carotene and 89% of thetocopherol and tocotrienol content (Tab. 11), which looksto be very high compared to physically refined palm oilproduced in Malaysia. Long retention time at relativelylow temperature combined with high steam consumptionare the necessary conditions to decrease the acidity tosufficiently low levels while preserving carotenoids, toco-pherols and tocotrienols.

More recently, it has been proved [33] that dual tempera-ture and low pressure (using an ice condensing vacuumsystem) can be used to produce an industrially physically

Tab. 11. Characteristics of golden palm oil produced byphysical refining at pilot scale [43].

Crudepalmoil

Degummedbleachedpalm oil

RBDgoldenpalm oil

FFA (as palmitic) [%] 3.8 0.08Phosphorus [ppm] 19 ,2Iron [ppm] 2.1 0.1Lovibond 51/4 (R/Y) 50/20 18/20Carotenes [ppm] 520 380 105Tocopherols/

tocotrienols [ppm]856 790 760

0.5 mbar, 180 7C, 3% steam, 180 min.

refined palm oil with improved quality parameters: morenatural color and higher tocopherol tocotrienol contents:dual temperature at 200220 7C combined with low pres-sure, 1 mbar (Tab. 12), seems to be the best option for amaximal retention of carotenoids, tocopherols and toco-trienols, for a good oxidative stability and efficientremoval of the FFA.

8.2 Red palm oil with high vitamin content

With the removal of FFA also comes in a considerableextent of removal of impurities. It has been shown that anefficient alkali refining plant is able to purify crude palm oilso effectively that it can be deodorized directly (withoutbleaching) or in the worst case with very small amounts ofnon-activated bleaching earths or silica [13]. Such a pro-cess will require very-good-quality crude palm oil (lowFFA and high DOBI), with the cleansing action of neu-tralization being mainly limited to phosphorus removalwhile keeping the carotenoids unaffected.

In some applications, the thermal bleaching would onlyoperate during deodorization conducted around 240 7Cand with a very short residence time, resulting in reducedlosses in tocopherols and tocotrienols and very goodoxidative stability for the final product (Tab. 13).

Thermal bleaching conducted at lower temperaturewould result in limited destruction of carotenoids, to-gether with keeping high amounts of tocopherols andtocotrienols in the oil.

Dedicated products issued from special refining proce-dures and labeled as Red Cooking Oils are available onthe Asian market: Carotino Cooking Oil and NutroleinGolden Palm Oil are the main representative products.Nutrolein for example (which is produced by Unitata Ber-had in Malaysia) is a superolein issued from dry-fractio-



Tab. 12. Relationship between process conditions (physical refining) and oil characteristics forgolden palm oil production [33].

Reference A B C D E

FFA (as palmitic) [%] 0.07 0.20 0.08 0.04 0.07 0.07Lovibond 51/4 (R/Y) 2.5/25 11.6/70 4.8/50 2.9/29 6.2/50 4.1/42Tocopherols/tocotrienols [ppm] 544 709 629 431 671 699OSI at 97.8 7C [h] 70.5 61.5 50.6 36.7 63.0 53.4

RBD palm oil refined under classical conditions.A: 200 7C, 1 mbar, 1.5% steam, 60 min.B: 220 7C, 1 mbar, 1.5% steam, 60 min.C: 260 7C, 3 mbar, 1.5% steam, 60 min.D: Dual temperature: 200220 7C, 1 mbar, 1.5% steam, 60 min.E: Dual temperature: 220240 7C, 3 mbar, 1.5% steam, 60 min.

Tab. 13. Characteristics of palm oil chemically refinedwithout bleaching earth [9].

Crudepalmoil

Degummedandneutralizedpalm oil

Degummed,neutralized anddeodorizedpalm oil

FFA (as palmitic) [%] 2.56 0.06 0.03M [%] 0.08 0.01 0.01I [%] 0.03 0.02 0.003Carotene [ppm] 580 579 1.0DOBI 3.1 Phosphorus [ppm] 16 3 0Tocopherols [ppm] 733 679 566Induction period at 100 7C [h] 49 34 44

nated, chemically refined high-quality crude palm oil. Itscarotenoid content is announced to be above 800 ppm,with a vitamin E concentration superior to 900 ppm.Same quality oils are available in the Latin American mar-ket, like Sioma Oil (produced by Danec S.A. in Ecuador),which is a more unsaturated variety of palm oil, obtainedfrom the hybrid palm.

8.3 Production of white soaps from palm

Production of white soaps from palm oil is not evident:the main problem is the too dark color (.5R 51/4) whichis usually achieved during the saponification step [44].

Good results (saponification color of 3R 51/4 or lighter)can only be expected when a crude palm oil of highquality is used for refining and if the refining procedure isperformed under optimized conditions. Recent researchhas shown [33] that very good saponification colors(around 2.5R 51/4) can only been obtained from a verylight RBD palm oil (0.6R 51/4) that can only be producedfrom crude palm oil having a DOBI above 3 (Tab. 14).

8.4 Feedstock for fractionated products

For usage of palm oil in dry fractionation, it is clear that itsproperties (mainly related to its TAG composition) shouldnot be modified during refining. Crude palm oil has nor-mally a PPO content below 5% which should stay at thatlevel before fractionation. Production of palm mid frac-tions (CBE) mainly consists in a maximum increase ofsymmetrical oleo-dipalmitin: POP; enrichment in asym-metrical PPO due to intra-esterification during the deo-dorization is of detrimental effect for the palm mid fractionquality [36]. The effect of deodorization time and temper-ature has been extensively studied by Willems and Padley[12]. The change of the ratio is significant if the oil is sub-jected to temperatures around 270 7C for long residencetimes. To avoid these intra-esterification problems, deo-dorization temperatures and residence times need to belimited; for this reason, chemical refining or physicalrefining at low pressure and shorter residence times arepreferred.

Also, a tailing effect which depends on the deodorizationconditions can be observed in the solid fat content profileof oleins [36]. This tailing effect observed in palm oleinsubjected to 280 7C for 4 h is significant compared torefining at 250 7C for 2 h; it is once again produced byintra-esterification of the fatty acids promoted at hightemperatures and resulting in early crystallization of palmolein during storage.

9 Refined palm oil quality

9.1 Effect of crude oil quality on color reversion

It is clear that good-quality refined palm oil cannot beproduced from low-quality oils. Crude palm oil with a verylow DOBI can be processed using a higher bleach-



Tab. 14. Production of white soaps with low saponification color through physical refining of palm oil[33].

Crude palm oil (DOBI: 3.3)

Refining conditions RBD oil color Saponification color

(R 51/4 Lovibond) (R 51/4 Lovibond)

Bleaching with 1.5% BE and refining at 280 7C 0.9 3.6Bleaching with 1.5% BE 1 0.4% AC and refining at 280 7C 0.7 2.8Bleaching with 2.5% BE 1 0.5% AC and refining at 280 7C 0.6 2.5

BE: Tonsil Optimum 210 FF.AC: activated carbon.

ing earth dosage (up to 56%) to produce acceptable FFAand color in refined products, but such a product has verypoor quality. As such, it cannot be called a refined productthat could meet the requirements of the customers. Asseen above, carotenoids in crude palm oil are easilyremoved during adsorptive bleaching and/or deodoriza-tion. The amount of carotenoids in the crude oil does notdetermine the residual color of the refined oil, which isprobably due to unknown high-molecular-weight com-pounds [45]. Every step in palm oil refining is important,and great care is taken in order to produce a stablerefined palm oil with minimal chances of color reversion.Although in most cases the color reversion is rectifiable, itmeans extra costs. Color reversion during processing isnormally associated with poor quality of the crude oil orwith improper degumming and bleaching processes. Thereversion could be due to colored pigments present in thecrude oil or as a result of the oxidation of carotenoidsduring deodorization; oils derived from badly damagedpalm fruits contain brown pigments from decomposedprotein and carbohydrates that are resistant to bleaching.Moreover, oxidized crude oils may contain colored com-pounds of quinoid nature developed from oxidation ofcolored materials. It seems that oxidation not only devel-ops new pigments but also stabilizes the pigmentsagainst their removal by adsorption [16].

It has been shown that bleached oil color cannot be usedto predict the final deodorized oil color and quality; inorder to determine the effect of the bleaching temperatureon the final oil quality, a simple test has been developed[46]. Palm oil was bleached at 95, 105, 120 and 135 7Cwith 2.5% bleaching earth. Bleached oil colors decreasedas the temperature increased, while the heat-bleached(refined) oil colors did the opposite. It was assumed thatthe rise in refined oil red color could be due to color for-mation caused by both oxidized fatty acids and oxidizedcarotenoids: elevated temperatures would increase theformation of the color bodies. Although the refined oilcolor rose with increasing bleach temperature, the oxida-

tive stability index (OSI) values indicated an optimumaround 120 7C, in agreement with other work [13, 32]. Itmay be argued that by increasing the bleaching earthdosage or by altering other refining parameters, oil of anyDOBI value could be adequately refined. However,another study showed [47] that the oxidative stability oflow DOBI refined palm oil is always lower, as compared torefined palm oils with DOBI above 2.3.

A bleachability test has been developed [33] at laboratoryscale by which the final color of palm oil could be pre-dicted. Six crude palm oils from different origins with aninitial FFA content between 1.9 and 7.2% were prepared.Afterwards, the samples were bleached at 260 7C for50 min at a pressure of 3 mbar, with the addition of onlysmall amounts of steam (to ensure good mixing and heattransfer). The low DOBI values combined with elevatedlevels of fatty acids and peroxides in some samples gavean indication that these oils were difficult to bleach (finalcolor 51/4 above 3) (Tab. 15). Moreover, a direct rela-tionship between the DOBI and the final color of the heat-bleached palm oil was observed [33]. A heat-bleachedpalm oil with color below 2R can be produced when crudepalm oil had a DOBI above 2.5. These observations con-firmed earlier findings [47] that DOBI values are a goodindicator for palm oil refinability. It was also shown [33]that the bleaching temperature did not affect the finalcolor after heat-bleaching. These observations confirmthat the bleached oil color cannot be used to predict therefined oil color.

9.2 Maximum retention of tocopherols andtocotrienols

The influence of the bleaching conditions on the toco-pherol and tocotrienol retention of physically refined palmoil has been reported (Tab. 16) [34]. The total quantity ofidentified tocopherols/tocotrienols increased duringbleaching in correlation with the bleaching earth quantity,



Tab. 15. Relationship between initial FFA content and DOBI of crude oils of different qualities (16)and final color of refined oils after a bleachability test at laboratory scale (260 7C, 3 mbar, 50 min) [33].

1 2 3 4 5 6

FFA (as palmitic) [%] 7.21 4.32 3.54 4.91 2.79 1.90DOBI 1.34 1.76 2.02 2.23 2.67 3.13Peroxide value [meq O2/kg] 2.33 3.79 3.15 3.54 0.36 1.03Oil grade bad poor poor poor fair goodLovibond (51/4) 3.1R/33Y 3R/35Y 2.2R/20Y 2R/20Y 1.3R/15Y 1.4R/15Y

Tab. 16. Effect of bleaching and deodorization conditions on residual tocopherol and tocotrienol contents (ppm) of palm oil(bleaching conditions: 110 7C, 50 mbar, 20 min; deodorization conditions: 250 7C, 3 mbar, 2.5 h) [34].

Crude Bleached RBD

0.5%acid-activatedclay



from 0.5%acid-activatedclay



a-tocopherol 190 220 233 223 147 125 150a-tocotrienol 131 155 162 156 140 112 147g-tocotrienol 339 291 286 250 213 201 251d-tocotrienol 113 127 135 206 51 69 62Total 773 794 815 834 551 506 610

which is in accordance with earlier observations [48]where regeneration of the free form from dimeric oresterified compounds was assumed. This release doesnot seem to be indiscriminate, as the g-tocotrienol con-tent decreases with increasing bleaching earth quantities.An average tocopherol and tocopherol retention of 80%was obtained after steam refining, which is quite high. Therelative concentration of single tocopherols/tocotrienolswas modified by steam refining, probably due to differ-ences in volatility among various forms and to differentstabilities under the refining conditions [47].

More recently, the influence of bleaching and deodoriza-tion conditions on total tocopherol and tocotrienol reten-tion has been studied [33] (Tab. 17). In this case, anincrease of tocopherol and tocotrienol contents was notobserved during bleaching. Pre-treatment with activecarbon decreased the b-carotene contents of thebleached and of the refined oil. Low quantities of steamdid not modify the b-carotene content of the refined oil,while affecting the final acidity and improving tocopheroland tocotrienol retention.

10 Future developments in palm oil refining

It becomes clear that good-quality palm oils are made inthe plantation and not in the factory. Indeed the quality ofa fully refined palm oil is highly dependent on and com-

pletely inseparable from the quality of the crude oil. Thehigh acidity of crude palm oil places physical refining asthe first option, mainly for economical reasons but also forenvironmental issues. The latest developments in therefining technology have been driven by the increasedattention to the nutritional quality. Optimizing the deodor-ization technology and the process conditions for max-imum retention of the natural characteristics will be animportant challenge for the future.

The development of vacuum systems (ice condensing)capable to reach low operating pressure (around 1 mbar)is very important [49] because it allows a reduction of thedeodorization temperature without affecting the vapor-ization efficiency.

Even if single-temperature deodorizers are still the mosteconomical for palm oil, working at different tempera-tures (dual temperature) is an asset to reach the bestcompromise between the required residence time fordeodorization (performed at low temperature) and heatbleaching and final stripping at higher temperature for abrief period.

Furthermore, a design including a structured packing foroil stripping, able to reduce steam consumption andoperating costs, perfectly fits with the requirements of ahigh-acidity oil like palm oil.



Tab. 17. Effect of pre-treatment and deodorization conditions on tocopherol and tocotrienol contents of palm oil [33].

Pre-treatment conditions$ Deodorization conditions FFA (aspalmitic)[%]

b-Carotene [ppm]before and afterdeodorization

Tocopherols andtocotrienols [ppm] beforeand after deodorization

Acid pre-treatment and bleaching with1.5% BE (95 7C, 30 min)

260 7C, 3 mbar, 0.2% steam, 50 min 0.09 107/2.0 808/684

260 7C, 3 mbar, 1% steam, 50 min 0.03 107/1.5 808/496Acid pre-treatment, bleaching with

1.5% BE (95 7C, 30 min) and treatmentwith 0.4% AC (80 7C, 30 min)

260 7C, 3 mbar, 0.2% steam, 50 min 0.08 87/1.0 797/659

260 7C, 3 mbar, 1% steam, 50 min 0.03 87/1.0 797/487

$ Crude palm oil: FFA, 5.3% (as palmitic); DOBI, 2.5; b-carotene, 459 ppm; tocopherol and tocotrienol content, 972 ppm.BE: Tonsil Optimum 210 FF; AC: activated carbon.

State-of-the-art is the introduction of a double scrubberunit (double condensing unit) for the improvement of thefatty acid purity in the distillate.

References

[1] K. G. Berger: Minor components of palm oil. Malays Oil SciTechnol. 2000, 9, 5659.

[2] B. Jacobsberg, C. H. Oh: Studies in palm oil crystallization. JAm Oil Chem Soc. 1976, 53, 609615.

[3] E. M. Goh, R. E. Timms: Determination of mono- and digly-cerides in palm oil, olein and stearin. J Am Oil Chem Soc.1985, 62, 730734.

[4] S. H. Goh, Y. M. Choo, S. H. Ong: Minor constituents of palmoil. J Am Oil Chem Soc. 1985, 62, 237240.

[5] A. S. Kulkarni: Studies of phosphatide and glycolipid com-position of palm oil from Maharashtra state in India. Pro-ceedings of International Palm Oil Conference, TechnologySection, PORIM, Kuala Lumpur (Malaysia) 1987, pp. 129132.

[6] S. H. Goh, S. L. Tong, P. T. Gee: Inorganic phosphate incrude palm oil: Quantitative analysis and correlations with oilquality parameters. J Am Oil Chem Soc. 1984, 61, 16011604.

[7] C. K. Ooi, Y. M. Choo, S. C. Yap, Y. Basiron, A. S. H. Ong:Recovery of carotenoids from palm oil. J Am Oil Chem Soc.1994, 71, 423426.

[8] T. Pantzaris: Palm Oil. In: Pocketbook of Palm Oil Uses. 5th

Edn. Ed. R. Perniagaan, Malaysian Palm Oil Board, KualaLumpur (Malaysia) 2000.

[9] P. A. T. Swoboda: Chemistry of refining. J Am Oil Chem Soc.1985, 62, 287292.

[10] K. G. Berger: Production of palm oil from fruit. J Am OilChem Soc. 1983, 60, 206210.

[11] H. B. W. Patterson: Handling and Storage of Oilseeds, Oils,Fats and Meal. Elsevier Science, Essex (UK) 1989.

[12] M. G. A. Willems, F. B. Padley: Palm oil: Quality requirementsfrom a customers point of view. J Am Oil Chem Soc. 1985,62, 454459.

[13] H. B. W. Patterson: Bleaching and Purifying Fats and Oils,Theory and Practices. AOCS Press, Champaign, IL (USA)1992.

[14] K. S. Law, T. Thiagarajan: Palm oil, edible oil of tomorrow. In:AOCS World Conference Edible Oils and Fats Processing,Basic Principles and Modern Practices. Ed. D. R. Erickson,AOCS Press, Champaign, IL (USA) 1990, pp. 260269.

[15] V. K. Lal, A. Gasper: Crude palm oil, quality requirements forgood refined products. Proceeding of PORIM InternationalPalm Oil Conference, Kuala Lumpur (Malaysia) 1991, pp.243254.

[16] J. Minal: Colour reversion of refined palm oil: Cause andremedy. Palm Oil Techn Bull. 1996, 2, 17.

[17] W. De Greyt, M. Kellens: Refining practice. In: Edible OilProcessing. Ed. W. Hamm, R. J. Hamilton, Sheffield Aca-demic Press, Sheffield (UK) 2000, pp. 79127.

[18] M. Kellens, W. De Greyt: Deodorization. In: Introduction toFats and Oils Technology. 3rd Edn. Eds. R. D. OBrien, W. E.Farr, P. J. Wan, AOCS Press, Champaign, IL (USA) 2000, pp.235269.

[19] J. C. Segers, R. L. K. M. van de Sande: Degumming. In:Theory and Practices in Edible Fats and Oils. Basic Princi-ples and Modern Practices. Ed. D. R. Erickson, AOCS Press,Champaign, IL (USA) 1990, pp. 8893.

[20] V. Gibon, A. Tirtiaux: Soft degumming: The simplest route tophysical refining of soft oils. Malays Oil Sci Technol. 1998,72, 4854.

[21] T. Thiagarajan, T. S. Tang: Refinery practices and oil quality.In: Proceeding of PORIM International Palm Oil Conference,Palm Oil Research Institute of Malaysia, Kuala Lumpur(Malaysia) 1991, pp. 254267.

[22] N. Hebendanz, W. Zschau: Impurities how to get rid ofunwanted by-products. In: World Conference on Oleo-chemicals. Ed. Th. H. Appelwhite, AOCS Press, Champaign,IL (USA) 1991.

[23] W. Zschau: Versuche zur Optimierung der Raffination vonPalml. Fette Seifen Anstrichm. 1982, 84, 493498.

[24] M. MacLellan: Palm oil. J Am Oil Chem Soc. 1983, 60, 368378.

[25] N. Loncin, B. Jacobsberg, G. Evrard: Lhuile de palme, pro-duction, proprits, raffinage, emplois. Rev Franc CorpsGras 1971, 18, 6981.

[26] M. Loncin: Sparation des pigments carotenodes de lhuilede palme. Olagineux 1975, 30, 7780.

[27] R. B. Morton: The oil content of filter cakes. Oils Fats Intern.1996, 12, 3135.

[28] P. Transfeld, M. Schneider: Countercurrent system cutsbleaching costs. Inform 1996, 7, 756767.



[29] J. De Kock, W. De Greyt, V. Gibon, M. Kellens: Dveloppe-ments rcents en matires de raffinage et de modifications:limination des contaminants dans les huiles alimentaires etrduction du taux dacides gras trans. OCL 2006, 12, 378384.

[30] T. C. Soon, D. B. Shaw, P. K. Stemp: Factors affecting thestability of oil during the physical refining of palm oil. In:Proceedings of PORIM International Palm Oil Conference,Palm Oil Research Institute of Malaysia, Kuala Lumpur(Malaysia) 1987, pp. 196202.

[31] Study Group for Industrial Processing of Fats and Oils:Bleaching of edible oils and fats. Cooperative Work of theGerman Society of Fat Science (DGF). Eur J Lipid Sci Tech-nol. 2001, 103, 505508.

[32] W. Zschau: Problems in bleaching differ with type of fat.Inform 1990, 7, 638644.

[33] Desmet Ballestra: Internal data.[34] M. Rossi, M. Gianazza, C. Alamprese, F. Stanga: The effect

of bleaching and physical refining on color and minor com-ponents of palm oil. J Am Oil Chem Soc. 2001, 78, 10511055.

[35] P. D. Howes, T. C. Soon, D. B. Shaw, P. K. Stemp: Bleachingearths, trends and developments. In: Proceeding of PORIMInternational Palm Oil Conference, Palm Oil Research Insti-tute of Malaysia, Kuala Lumpur (Malaysia) 1991, pp. 5557.

[36] W. L. Siew, Y. Mohammad: Effect of refining on chemical andphysical properties of palm oil products. J Am Oil ChemSoc. 1989, 66, 11161119.

[37] K. N. Nasirullah: Irradiation bleaching of palm oil, palm oleinand palm stearin. J Am Oil Chem Soc. 2004, 81, 517518.

[38] W. De Greyt, M. Kellens: Deodorization. In: Baileys IndustrialOil and Fat Products. 6th Edn. Vol. 5. Ed. F. Shahidi, JohnWiley & Sons, Inc., Hoboken, NJ (USA) 2005.

[39] A. Hvolby: Removal of nonhydratable phospholipids fromsoybean oil. J Am Oil Chem Soc. 1971, 48, 503509.

[40] A. Kunton, W. L. Siew, Y. A. Tan: Characterization of palmacid oil. J Am Oil Chem Soc. 1994, 71, 525528.

[41] V. Petrauskaite, W. De Greyt, W. M. Kellens: Physical refiningof coconut oil: Effect of crude oil quality and deodorizationconditions on neutral oil loss. J Am Oil Chem Soc. 2000, 77,581586.

[42] P. Faessler: Recent developments and improvements inpalm oil stripping and fatty acid distillation. In: Proceeding ofWorld Conference on Palm Coconut Oils for the 21th Cen-tury, Eds. E. C. Leonard, E. G. Perkins, Kuala Lumpur(Malaysia) 1998, pp. 6772.

[43] E. Deffense: Steam refining and golden palm oil. Proceedingof PORIM International Palm Oil Conference, Kuala Lumpur(Malaysia) 1993.

[44] S. Ahmad, H. Kifli: Improvement of whiteness of palm-basedsoaps and colour stability of fatty acids via peroxidebleaching. In: Proceedings of Second World Conference onDetergent. Ed. A R Baldwin, AOCS Press, Champaign, IL(USA) 1987, pp. 250256.

[45] M. S. Fraser, G. Frankel: Colored components of processedpalm oil. J Am Oil Chem Soc. 1981, 58, 926931.

[46] D. D. Brook, D. Shaked: Bleaching difficult to bleach palmoil. Proceedings of the PORIM International Palm Oil Con-gress, Kuala Lumpur (Malaysia) 1996, pp. 2732.

[47] V. K. Lal, A. Gasper: Crude palm oil Quality requirementsfor good refined products. PORIM International Palm OilConference, Chemistry and Technology, Kuala Lumpur(Malaysia) 1991, pp. 243253.

[48] A. B. Gapor, M. D. Top, K. G. Berger, T. Hashimoto, A. Kato,K. Tanabe, H. Mamuro, M. Yomaoka: Effects of processingon the content and composition of tocopherols and toco-trienols in palm oil. In: Palm Oil Product Technology in theEighties. Eds. E. Peshparajah, M. Rajadurai, ISP, KualaLumpur (Malaysia) 1983, pp. 145156.

[49] A. J. Dijkstra: Stripping medium requirements in continuouscountercurrent deodorization. J Am Oil Chem Soc. 1999, 76,989993.

[Received: December 22, 2006; accepted: February 21, 2007]


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