Soapstock and Deodorizer Distillates From North American

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Review

Soapstock and deodorizer distillates from North Americanvegetable oils: Review on their characterization,

extraction and utilization

Marie-Josee Dumont, Suresh S. Narine *

Alberta Lipid Utilization Program, Department of Agricultural Food and Nutritional Science, 4-10 Agriculture/Forestry Centre,

University of Alberta, Edmonton, Alberta, Canada T6G 2P5

Received 27 November 2006; accepted 5 June 2007

Abstract

Soapstock and deodorizer distillates are the major by-products from vegetable oil refining. They have little commercial value and aresold at a fraction of the oil cost. However, their characterization reveals the presence of numerous types of compounds, which could beextremely valuable if extracted at low cost. The literature in this area is discontinuous and warrants the effort to produce a comprehensivereview. The aim of this review is to combine and condense the body of research performed on these materials, as well as to suggest thebest routes for characterization and extraction. Utilization of the components is also discussed. 2007 Elsevier Ltd. All rights reserved.

Keywords: Vegetable oils; Soapstock; Deodorizer distillate; Characterization; Extraction; Utilizations

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9582. Crude oil refining. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 958

2.1. Degumming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9582.2. Chemical refining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9592.3. Physical refining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9592.4. Bleaching, winterization and deodorization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9602.5. Other refining methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 960

2.5.1. Refining by membrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9613. Characterization of by-products obtained from oil refining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 961

3.1. Characterization of soapstocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9613.2. Characterization of deodorizer distillates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9623.3. Characterization of acid oil water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 963

4. Utilization of components from refining oil waste streams. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9634.1. Soapstock and animal diet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9634.2. Biodiesel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9644.3. Drilling fluids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9654.4. Specialized applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 966

0963-9969/$ - see front matter 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.foodres.2007.06.006

* Corresponding author. Tel.: +1 780 492 9081; fax: +1 780 492 7174.E-mail address: [email protected] (S.S. Narine).

www.elsevier.com/locate/foodres

Food Research International 40 (2007) 957974
mailto:[email protected]:[email protected]


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4.4.1. Multigrade lubricating greases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9664.4.2. Biosurfactants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9664.4.3. Fatty acid modification diacylglycerols (DAG) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9674.4.4. Derived films . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 967

5. Extraction of valuable components from soapstocks and deodorizer distillates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9675.1. Soapstock. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 967

5.1.1. Extraction of fatty acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 967

5.1.2. Extraction of gossypol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9685.2. Extraction of deodorizer distillate components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 968

5.2.1. Extraction of tocopherols, sterols and squalene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9685.2.1.1. Solvent extraction and crystallization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9695.2.1.2. Supercritical fluid extraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9695.2.1.3. Enzymatic reaction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9715.2.1.4. Molecular distillation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9715.2.1.5. Other methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 971

6. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 971Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 972References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 972

1. Introduction

Edible oils are produced primarily from oilseeds. Totalworld production of important oilseeds is forecasted toreach395 million tonnes for the 2005/2006 crop year1 of whichCanada will contribute14 milliontonnes.2The crude or unre-fined oils extracted from oilseeds generally consists of freefatty acids (FFA), mono-, di-, and triacylglycerides (MAGs,DAGs, and TAGs), phosphatides, pigments, sterols, toc-opherols, glycerol, hydrocarbons, vitamins, proteins frag-ments, trace amounts of metals, glycolipids, pesticides and

resinous and mucilaginous materials among others(Cheryan, 1998). The method chosen for oil extraction ishighly dependent upon the nature of the oilseed, the econo-mic feasibility of the extraction process and market demand.

The first step in producing oils for edible applicationsinvolve the separation of the oil (containing more than90% TAGs) from other solid components of the seeds. Forthe majority of oilseeds, this is achieved by pressing followedby solvent extraction (Young, Biernoth, Krog, Davidson, &Gunstone, 1994). This crude oil is then refined in order toremove free fatty acids and other non-TAG componentswhich contribute to undesirable flavor, odor and appear-ance. Methods of treatment include deacidification, neutral-ization, bleaching, deodorization, etc. (Anderson, 1953).

A significant amount of by-products such as soapstocks,deodorizer distillates and acidic water are produced fromcrude oil refining processes, and these by-products arepotentially harmful to the environment. In the UnitedStates for example, soybean oil refining processes poten-tially produce 100 million pounds of soapstock whichretails at 1/10th the cost of the refined vegetable oil.3

Due to human population increase, the consumption ofedible oils is expected to increase, thereby resulting inincreased production of these by-products. It is thereforeimportant to study and explore ways of mitigating theirnegative environmental impact as well as derive valueadded products. Significant potential exists for the extrac-tion of valuable and useful chemicals from these non-TAG waste products.

In order to convert the waste from the oil refining pro-cess to value added materials, it is imperative that econom-ically feasible chemical modification, identification and

separation techniques be developed. This presents a consid-erable challenge given the chemical complexity of thesewaste materials.

2. Crude oil refining

Crude oil is refined using several processes to removeundesirable components before making it available forhuman consumption. These processes are widely coveredin the literature. This section provides information on theby-products produced after crude oil refining. Fig. 1 sum-marizes the conventional processing steps encounteredfrom crude to refined rapeseed oil and Table 1 summarizestheir advantages and disadvantages.

2.1. Degumming

The first refining step involves the removal of phospho-lipids using the degumming process. These molecules areeither present in a hydratable or a non-hydratable form.The non-hydratable form occurs when the phospholipidis combined with calcium, magnesium or iron cations. Thisform must be treated with acid in order to convert them tohydrated gums. The hydratable form is treated by waterdegumming and directly converted into hydrated gums.

These gums are then removed by centrifugation.

1 http://www.fao.org/es/ESC/en/20953/21017/highlight_27527en.html.2 http://www.agr.gc.ca/mad-dam/e/sd1e/2006e/mar2006e.htm.3 http://www.landandlivestockpost.com/technology/050102soybyproducts.

htm.

958 M.-J. Dumont, S.S. Narine / Food Research International 40 (2007) 957974
http://www.fao.org/es/ESC/en/20953/21017/highlight_27527en.htmlhttp://www.agr.gc.ca/mad-dam/e/sd1e/2006e/mar2006e.htmhttp://www.landandlivestockpost.com/technology/050102soybyproducts.htmhttp://www.landandlivestockpost.com/technology/050102soybyproducts.htmhttp://www.landandlivestockpost.com/technology/050102soybyproducts.htmhttp://www.landandlivestockpost.com/technology/050102soybyproducts.htmhttp://www.agr.gc.ca/mad-dam/e/sd1e/2006e/mar2006e.htmhttp://www.fao.org/es/ESC/en/20953/21017/highlight_27527en.html


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2.2. Chemical refining

The degumming step is not always necessary prior tochemical refining. The best known and the most widelyused chemical refining process is the caustic soda process.

Phosphoric acid is added to the crude oil in order to precip-itate the phospholipids; this is followed by the addition ofan alkaline solution. The alkaline solution neutralizes thefree fatty acids (reaction 1) and any excess phosphoric acid(reaction 2). Reaction of the alkaline solution with fattyacids leads to the formation of soap. The soapstock createdis then continuously separated from crude oil by centrifu-gation (OBrien, 2004):

RCOOH NaOH ! RCOONa reaction 1

H3PO 3NaOH ! Na3PO4 reaction 2

Conventional chemical refining is time consuming andhas several disadvantages. It has substantial energyrequirements and the side products formed (soapstockand deodorizer distillate) are not environmentally friendlyor commercially valuable. Furthermore, the chemical pro-cess leads to considerable oil loss; soapstock can hold as

much as 50% of its weight of neutral oil. Despite havingseveral disadvantages, it is still used in many industriesbecause of the successful reduction of free fatty acid(FFA) content to the desired level.

Miscella deacidification involves slight modification ofthe chemical refining process. In this process, the oil ismixed with hexane to create miscella. The miscella aremixed with sodium hydroxide in a neutralization step andthen reacted with phosphatides. This process also inducesdecolorization. Soapstock are removed by centrifugationwhich results in minimal loss of neutral oil, however it isvery expensive and solvent removal requires several steps.Miscella deacidification is almost only used for the refining

of cottonseed oil because a lighter color of final product isobtained compared to using the classical methods (Bhosle& Subramanian, 2005).

2.3. Physical refining

Physical refining processes use steam stripping undervacuum to avoid chemical neutralization. It is a simplifiedoperation that removes free fatty acids, unsaponifiable sub-stances, and pungent compounds and also reduces theamount of oil lost. It consumes less steam, water andpower, and requires less capital investment than the chem-

ical refining process (Cvengros, 1995).Two similar physical refining processes can be used

depending on whether the raw material is a low phosphatideor high phosphatide crude oil. The physical treatment of lowphosphatide crude oil consists of a series of steps involvingdry degumming, dewaxingfractionationhydrogenation,steam distillation and deodorization. The treatment of highphosphatide crude oil consists of an acid refining or degum-ming step prior to dry degumming or bleaching. The lowphosphatide crude oil treatment does not require additionalacid refining or degumming steps (OBrien, 2004). Accordingto a review on the subject (Cmolik & Pokorny, 2000), there

Crude oil

Water degumming

or

Acid degumming

Physical refining

Bleaching

Winterization

Deodorization

Chemical refining

Refined oil

Fig. 1. Oil refining processing steps.

Table 1Different refining methods and their advantages and disadvantages

Refining type Advantages Disadvantages

Chemical refining (1) Functional process(2) Not restricted by the oil type(3) Successful reduction of FFA

(1) Production of side-products(2) Expensive process(3) Remove high % of oil

Physical refining (1) Less expensive than chemical refining(2) Less by-products generated than chemical refining(3) Less energy consumed than chemical refining

(1) Not suitable for all types of oils(2) Requires high temperature and vacuum(3) Can form side reaction products

Membrane (1) Non-polluting(2) Low energy demand

(1) Improvement of equipment needed

Miscella deacidification (1) Minimal loss of oil (1) Soapstock generated(2) Not suitable for all types of oil

(3) Expensive

M.-J. Dumont, S.S. Narine / Food Research International 40 (2007) 957974 959
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are seven different variations of physical refining proceduresthat can be applied depending on the type of plant design.

Physical refining of crude vegetable oil has severaladvantages over traditional alkali refining processes. Forexample, there are improvements with regard to simplicityof the procedure, product yield, energy conservation, and

reduced generation of environmental pollutants. Thereare also many drawbacks such as not all types of oils aresuitable for this process (Hartman, 1978). The use of hightemperatures and high vacuum often results in the forma-tion of side products such as polymers and trans isomers(Sengupta & Bhattacharyya, 1992).

2.4. Bleaching, winterization and deodorization

Carotenoids, chlorophyll pigments, residual soap, phos-pholipids, metals and oxidized products are removed by

bleaching. These components are absorbed by heated clay.Fig. 2 shows the chemical structures of zeaxanthin (a typeof carotenoid found in corn), chlorophyll and L-a-phospha-tidylcholine (a type of phospholipid found in soybean). Theoil is then rapidly cooled (winterized) to solidify traces ofwax, which are esters of fatty acids or long chain alcohols.

These particles are then easily removed by filtration.Deodorization removes aldehydes, ketones and other vola-tile components that would otherwise impart flavor andodor.

2.5. Other refining methods

Several other refining processes are currently underdevelopment. Refining by membrane will be discussed inthis review because it is a soapstock free process. Themiscella deacidification process is also introduced in this

HO

OH

Mg

N N

NN

O

H3CO

OO

O

H3C(CH2)14 O O

P

O

+N

O

O O

(CH2)7CH=CHCH2CH2CH2(CH2)4CH3

O

O-

(A)

(B)

(C)

Fig. 2. Chemical structures of (a) zeaxanthin, (b) chlorophyll and (c) L-a-phosphatidylcholine.



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review because it is used mostly for refining cottonseedoil.

2.5.1. Refining by membrane

Membrane refining is a simple process offering manyadvantages over conventional processes. In the membrane

refining process, different compounds are separated basedon the difference between their molecular weights, particleshapes and particle sizes. The membrane-based technologyis being actively investigated and is sought as an alternativeto chemical and physical refining because it is non-pollutingand has a low energy demand. Raman, Cheryan, and Raj-agopalan (1996) have shown that by using a nanofiltrationprocess, no alkali is required and no soapstock is formed.The membrane refining process is very promising but sev-eral difficulties must be surmounted before it can replaceconventional refining methods. Several research groupsare actively working to improve the equipment, enhancethe efficiency and increase the selectivity of the membranes

(Lin, Rhee, & Koseoglu, 1997). For example, studies havedemonstrated that it is possible to remove phosphorous,water and FFA by a single filtration step (Pioch, Largueze,Graille, Ajana, & Rouviere, 1998; Koris & Vatai, 2002).However, sterols that have beneficial health effects are alsoremoved from the oil (Hafidi, Pioch, & Ajana, 2005).

3. Characterization of by-products obtained from oil refining

3.1. Characterization of soapstocks

Soapstocks are mostly wet lipidic mixtures. Their phys-

ico-chemical properties tend to change with the type of veg-etable oil source, seed processing, and handling and storageconditions. To limit chemical changes that can occur in themixture, the American Oil Chemists Society (AOCS) hasdeveloped recommended handling and storage conditions(method G1-40). The AOCS has also developed severalother protocols: extraction of neutral oil and volatile sol-vent content (method G5-40), measurement of neutral oilcontent (method G5-40), extraction of fatty matter(method G3-53) and more specifically extraction of fattymatter for palm and coconut soapstock (method G4-40)(Firestone, 1998).

The compositional determination of soapstock began inthe mid-nineteen fifties. At that time, the recorded datawere acid and iodine values, unsaponifiable matter content,volatile matter content, free fatty acid content and neutraloil and ash contents (El-Shattory, 1979; Keith, Bell, &Smith, 1955; Stansbury, Cirino, & Pastor, 1957). The rhe-ological characteristics of soapstock were studied later(Hiraldo, Herrera, Luque, & Montes, 1989).

The first attempt to characterize soapstock was achievedin 1987 (Waliszewski, 1987). Since then, three other papershave described methods for the characterization of soap-stock (Dowd, 1996, 1998; Durant, Dumont, & Narine,2006). Waliszewski (1987) utilized gas chromatography

(GC) for the fatty acid analysis of soybean, sunflower, saf-

flower, cotton seed and corn germ soapstock. Waliszewskiet al. neutralized the soapstock mixture with acid anddecreased the viscosity with addition of ethanol prior tothe GC analysis. The analysis of fatty compounds requiresrigorous labor, especially in the case of soapstock, wherethe mixture has components with differing degrees of polar-

ity. The author was able to quantify fatty acids that havesimilar retention times (for example linoleic and linolenicacid) without the need for derivatization prior to chro-matographic analysis. This research was the first introduc-tion to the analysis of soapstock by gas chromatography.Since the publication of this research, derivatization tech-niques have been introduced for the characterization ofthese materials (Dowd, 1996, 1998; Durant et al., 2006).

It was in 1996 that a complete characterization of soap-stock was accomplished. Dowd (1996) characterized 39samples of cottonseed soapstock. In this work, Dowd car-ried out some of the AOCS protocols such as total fattyacid and neutral oil extraction (G3-53 and G5-40 respec-

tively), analysis of nitrogen (Ba 4e-93) and total gossypolcontent (Ba 8-78). Analysis of soapstock was performedusing gas chromatographymass spectroscopy (GCMS).Sample preparation required a drying step followedby derivatization using pyridine, hexamethyldisilazane(HMDS) and trifluoroacetic acid (TFA). The silyl deriva-tives were found to be more volatile, less polar, thermallymore stable and could displace chromatographic peaks ofsoap counterions at the same position of their correspond-ing free fatty acids. From this work, cottonseed soapstockwas found to be mainly composed of moisture and solvent(approx. 49%), fatty acids (approx. 60% on a dry basis),

organic phosphates, monoglycerides, diglycerides, triglyc-erides, sterols, polyalcohols, carbohydrates and other mis-cellaneous components including gossypol. The majority ofthese classes of organic compounds are found in differenttypes of soapstock, however gossypol (a polyphenolic com-pound) is found only in cottonseed sources. Dowd (1996)found a gossypol content of 7.5% in cottonseed soapstock.

Dowd (1996, 1998) reported that the amount of fattyacids extracted by solvent (using AOCS official methodG3-53) was found to be in accordance with the resultsgiven by GC and phosphorus analysis but the percentageof neutral oil recovered from soapstock was different fromthe AOCS method G5-40. Dowd (1998) also found that theamount of saturated fatty acids was higher than their con-centration within the refined oil. Dowd explained theseresults by the fact that saturated fatty acids in several veg-etable oils (i.e. corn, cottonseed, sunflower, soybean andsafflower) are positioned on the triglyceride backbone atthe sn-1 and sn-3 positions. These fatty acids are releasedfrom the triglyceride because hydrolysis by chemicals andenzymatic glycerides occurs generally at these positions.The fatty acid composition of different sources of soap-stock is presented in Table 2.

Although Dowds study allowed for the total composi-tion of soapstock to be determined, the choice of a more

polar column may have helped with the separation of



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compounds such as TMS-esters of linoleic and linolenicacid. In addition, the high temperatures utilized caused apartial degradation of the fatty acids. Application of thederivatization technique used by Dowd (1996, 1998) cou-

pled with a medium polar column (instead of a low polaritycolumn) allowed for the separation of linoleic and linolenicacid (Durant et al., 2006). This application of Dowdsderivatization technique also has the advantage of allowingthe separation of monoolein and monolinolein which havesimilar retention times. In addition, this method was suc-cessful at separating components of deodorizer distillatesamples (discussed below).

3.2. Characterization of deodorizer distillates

Deodorizer distillates are complex mixtures like soap-

stocks. Their commercial value however, is mainly depen-dent on their tocopherol content. In fact, the majority ofresearch published covers the characterization and recuper-ation of high-value chemicals such as tocopherols and ster-ols that are present in the deodorizer distillates. There arefew publications relating to the full analysis and character-ization of the mixture. Table 3 presents the tocopherol andsterol content of some deodorizer distillate sources.

As with soapstocks, methods have also been developedby the AOCS for the characterization of deodorizer distil-lates. Method CE3-74 is one such method and involves the

use of gas liquid chromatography (GLC) with a packedglass column. Saponification is preferred prior to perform-ing the GC analysis to diminish potential overlappingpeaks in the tocopherol region. This procedure provides arough estimation of the tocopherol and sterol content.However, the chromatogram does not show any saponified

matter (mainly fatty acids) because saponification neutral-izes such compounds. According to literature (Feeter, 1974;Marks, 1988), the use of a packed column, therefore, is nota suitable method for the separation of components fromthe deodorizer distillates. Research by Feeter (1974) usingpacked column gas chromatography analysis showed thatthis method is not suitable for the separation of the trim-ethylsilyl ether derivatives ofb-, c- and d- tocopherols thatco-elute with sterols. The author also identified at least fiveother pairs of co-eluted compounds. Avoiding the saponi-fication step does not resolve the co-elution problem(Marks, 1988). However, the method could be useful fora rough estimation of the tocopherol and sterol content,

but sample preparation is 23 times longer than capillarygas chromatography (Marks, 1988) which is also a moreaccurate technique.

Capillary gas chromatography is a simpler, faster tech-nique that can lead to the characterization of all the com-ponents in deodorizer distillates depending on parameterssuch as the distillate pre-treatment and the choice of col-umn. It has been found that saponification is not necessarywhen utilizing this method. Not all characterization carriedout using this technique have been successful without co-elution but the resolution is definitively better than theGC analysis utilizing a packed column This can be ratio-

nalized by the low impedance of the capillary columnallowing for the use of a very long column which providesvery high efficiencies.

Verleyen et al. (2001), by means of this technique, char-acterized several types of deodorizer distillates such assoybean, canola, sunflower and corn. This study involvedthe characterization of both saponified and derivatizeddeodorizer distillates. Comparing chromatograms of theabove two studies, it was discovered that free fatty acidsare not present after saponification of the samples. Fur-thermore, numerous peaks located in the region beforethe sterols and tocopherols remain unidentified. Some ofthese peaks appear at the same retention time as the iden-tified fatty acid peaks. The authors also report two pairs ofcompounds that co-eluted when the distillates were deriva-tized. Brassiscasterol and a-tocopherol co-eluted as well asc- and d-tocopherol. The authors state that the separationof the latter pair of compounds could only be achieved byusing high performance liquid chromatography (HPLC),contradicting the results reported earlier by De Greyt,Petrauskaite, Kellens, and Huyghebaert (1998) who per-formed HPLC analysis on different types of vegetable oils.

The methodology based on the silylation derivatizationtechnique described earlier (Section 3.1) could provideassistance with the co-elution issue (Durant et al., 2006).

HMDS used in the silyl derivatization step is a milder base

Table 2Fatty acid content of different soapstock sources

Fatty acids Concentration (%) reported on a dry basis

Cottonseed(Dowd, 1996)

Corn(Dowd,1998)

Peanut(Dowd,1998)

Canola(Durant et al.,2006)

Myristic acid 0.24 0.031 0.066 ndPalmitic acid 9.31 8.62 8.62 4.63Palmitoleic acid 0.18 tr tr 0.15Stearic acid 0.96 0.507 0.458 ndOleic acid 6.07 9.36 11.6 15.57Linoleic acid 16.50 17.8 7.75 3.31Linolenic acid nd nd nd 0.24Arachidic acid 0.077 0.076 tr 0.12

nd = not detected; tr = traces.

Table 3

Tocopherol and sterol content of different deodorizer distillate sources

Component Concentration (g/100 g)

Soybean(Verleyenet al., 2001)

Sunflower(Verleyenet al., 2001)

Rapeseed(Verleyenet al., 2001)

Canola(Durantet al., 2006)

d-Tocopherol 5.00 nd 0.25 6.56b-Tocopherol 0.44 nd 0.16 ndc-Tocopherol 11.00 0.3 2.41 13.51a-Tocopherol 0.82 4.76 1.12 0.55Brassicasterol nd nd 2.2 ndCampesterol 5.36 1.58 3.65 2.59Stigmasterol 4.46 2.04 nd 2.27Sitosterol 8.12 8.60 5.15 2.66

nd = not detected.



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in comparison to the commonly utilized N,O-bistrimethyl-silyltrifluoroacetamide (BSTFA) (Marks, 1988; Verleyenet al., 2001) but the HMDS silylation method requiresTFA as a catalyst. The use of a medium polar column withthese silylation conditions allowed for successful separationof fatty acids, sterols, tocopherols and glycerides. This

method also successfully separated brassiscasterol and a-tocopherol as well as c- and d- tocopherols.The use of expensive techniques such as capillary super-

critical fluid chromatographymass spectroscopy also doesnot appear to be a suitable method and could be consideredas one of the less successful techniques due to high cost andtime consumption. Snyder, Taylor, and King (1993) utilizedthis technique and focused on the tocopherol, squalene andsterol characterization of deodorizer distillate samples. Theauthor suggested that presence of high molecular weightspecies such as DAGs and TAGs make characterizationvery difficult. However, this technique was successful forthe characterization of tocopherols, squalene and sterols.

It may be possible to entirely characterize the distillate uti-lizing this method, but further research involving tempera-ture and pressure must be carried out to compare the effectson the separation of all the components of the distillate. Toillustrate this particular problem, Table 4 shows the ther-mophysical properties of some pure compounds found insoybean deodorizer distillates (Araujo, Machado, & Meire-les, 2001). As can be seen in Table 4, the critical temperatureand pressure for oleic and linoleic acid almost overlap.

Another potentially expensive method has been devel-oped by Ramamurthi and McCurdy (1993) involvinglipase-catalyzed modification of fatty acids. This analysis

was carried out on canola, mixed and soy distillates. Thevolatile fractions were removed by vacuum distillation,concentrating the tocopherol and sterol fractions. Theircharacterization was achieved using GC. However, thetemperatures suggested by this method are not appropriateand did not provide good resolution of peaks.

3.3. Characterization of acid oil water

Acid oil water is a by-product of vegetable oil refiningthat is heavily contaminated with fatty matter. Acid oilwater has almost no economic value and as a consequence

limited publications are available on this subject. To ourknowledge, there are only two papers (Johansen, Sivasothy,Dowd, Reilly, & Hammond, 1996; Mag, Green, & Kwong,

1983) that actually report on acid oil water characterization.The main objectives for the above mentioned research wasto characterize the mixture and lower the fat content. Thefat content of waste water must be below 150 ppm in orderto be discharged to municipal sewers (Mag et al., 1983).

Mag et al. (1983) have studied the recovery of acid oil by

continuous acidulation of soapstock. They have demon-strated that continuous acidulation of soapstock, decanta-tion of the bulk acid oil from acid water and acid watertreatment in a coalescer (for further separation of the emul-sified acid oil) can reduce the fat content of acid water tobelow 150 ppm.

Johansen et al. (1996) have analyzed acid water fromsoybean, canola, sunflower, peanut, cottonseed and cornoil soapstock using three methods: (1) GC and electron-ionization MS, (2) GC and chemical-ionization MS and(3) HPLC with strong-acid ion exchange resin. With theexception of the lactic acid (obtained from anaerobic fer-mentation of soapstock or unrefined vegetable oil), all

identified peaks can be linked to components found inthe plant tissues. All major low-molecular weight organiccomponents that have been identified for each source ofacid water are presented in Table 5.

4. Utilization of components from refining oil waste streams

This section discusses the different valuable soapstockand deodorizer distillate compounds that are currentlyused for direct industrial applications or have been investi-gated for potential high-value and novel applications.

4.1. Soapstock and animal diet

Soapstocks are increasingly being used as an animal feedadditive, particularly in pig and poultry diets. It has noharmful effects (beyond gossypol) and can be used in a sim-ilar way to fat since it contains a high concentration offatty acids. Gossypol is a toxic substance that needs to beremoved from cottonseed soapstock sources prior to beingused for animal feedstock. Extraction of gossypol will becovered in a later section. When soapstock is added intomeal, it can improve the palatability, increase the energydensity of the diet, reduce dust, help heat stress conditions,and improve pelleting of feed products by reducing feedparticle separation. It also minimizes the build up of feedparticles on equipment used for feed mixing at the mill.However, long chain fatty acids are difficult to digest inanimals (Johnson & McClure, 1973), therefore soapstockmust be added in small amounts (approximately 3.5%)(Bock et al., 1991).

The percentage of polyunsaturated fatty acids containedin a soapstock mixture is another parameter that has to betaken into consideration. A broilers taste can depend onthe percentage of polyunsaturated fatty acids in the diet(Lipstein, Bornstein, & Budowski, 1970). More recently(Pardio, Landin, Waliszewski, Badillo, & Perez-Gil,

2001), it has been shown that the addition of up to 1% of

Table 4Critical temperature and pressure of pure compounds found in soybeandeodorizer distillates

Compounds Critical temperature (C) Critical pressure (atm)

Palmitic acid 507 14.5Oleic acid 523 12.3Linoleic acid 523 12.2a-Tocopherol 624 8.09Stigmasterol 576 9.09

Squalene 565 6.44



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polyunsaturated fatty acids from soybean soapstock tobroilers diet from one to seven weeks of age increased theirweight by approximately 1.7 g. Cottonseed soapstockwhich is widely used to supplement animal diets containsgossypol, the predominant cottonseed plant pigment andmajor toxic ingredient (Adams, Geissman, & Edwards,

1960; Kovacic, 2003). As discussed earlier, in order to pro-duce cottonseed edible oil, gossypol is typically removedduring the oil refining process and ends up in the soap-stock. Therefore, soapstock has to be added in a limitedamount (Kuk & Tetlow, 2005) since 0.1% of gossypol isthe upper limit that chickens can absorb without havinggrowth rate problems (Lipstein & Bornstein, 1964a).

A comparative study between acidulated cottonseed andsoybean soapstocks in chicken feed has shown that chickenlipid oxidation is lower when the animals are fed with acid-ulated soybean soapstock (Bartov, Lipstein, & Bornstein,1974). Soybean oil soapstock which is produced on a mas-sive scale is considered to be a suitable substitute for soy-

bean or corn oil in soybean meal-sorghum animal diets(Bartov et al., 1974) and does not affect the compositionof hen egg yolk (Pardio et al., 2005). However, a recentstudy (Bruce et al., 2006) showed that the addition of soy-bean soapstock to pigs and roasters diet can decrease theamino acid digestibility and induce subsequent problemssuch as growth performance.

4.2. Biodiesel

The use of biodiesel over conventional diesel has severaladvantages. It substantially decreases emission of carbon

dioxide, particulate matter, carbon monoxide, sulfur oxide,volatile organic compounds and unburned hydrocarbonsbut it increases nitrogen oxide emission which causes respi-ratory problems when found at the ground level (Fernando& Jha, 2006; Usta et al., 2005). Production of biodieselreduces fuel costs by 25% in comparison to diesel (Haas,

2005), however, biodiesel cannot be produced in sufficientquantity to meet the demand of a whole country. Forexample, only 14% of the US demand in diesel per yearcould be satisfied if all the animal and vegetable fat contentin the country was utilized for its production (Van Gerpen,2005).

As previously mentioned, soapstocks are a good sourceof fatty acids, and are cheap in comparison to vegetable oil.Conversion of their FAs to FAMEs or fatty acid alkylesters (FAAEs) has been studied for use in biodiesel formu-lations. Table 6 summarizes the major conversion methodsinvestigated so far (Haas, Bloomer, & Scott, 2000; Haas,Michalski, Runyon, Nunez, & Scott, 2003a; Haas & Scott,

1996; Tuter, Aksoy, Gilbaz, & Kursun, 2004).Haas et al. (2000) and Haas et al. (2002) carried out the

esterification of fatty acids from soapstock by saponifica-tion of glycerides and phosphoglycerides by alkalinehydrolysis followed by an acid-catalyzed esterification ofthe remaining salt of fatty acids. These steps ensure thetotal hydrolysis of the mixture. Complete esterificationwas achieved by adding FFA:methanol:acid in the propor-tion of 1:30:5. After 10 min, the reaction was 99% com-plete. This method requires subsequent washes withNaCl, NaHCO3 and Ca(OH)2 to remove the free fattyacids from the remaining solution (Haas et al., 2003a).

Table 5Major low-molecular weight organic compounds found in different sources of acid water

Compounds Concentration (g/L)

Canola Corn Cottonseed Peanut Soybean Sunflower

Phosphoric acid 0.85 0.82 0.07 0.04 0.79 1.17a-Glycerophosphate 0.34 0.82 12.4 Trace 0.55 14.0

b-Glycerophosphate 0.03 0.11 6.17 0.01 0.40 3.47Glycerol 0.13 0.11 19.4 0.03 0.47 5.96Myo-Inositol 0.02 1.21 3.63 0.03 0.44 1.57Myo-Inositol-1-phosphate 0.03 0.81 6.31 0.75 4.10a-Glycerophospho-1-myo-inositol 0.04 0.20 1.18 0.27

Table 6Comparison between the different methods used for the conversion of fatty acids into fatty acids methyl esters or fatty acids alkyl esters

Author Method Conversion Advantage of the method Disadvantage of the method

Haas and Scott (1996) Enzymatic catalysis FFA to FAAEs Not significant Low conversion factor63%

Tuter et al. (2004) Enzymatic catalysis FFA to FAAEs Not significant Low conversion factor50% to 63%

Haas et al. (2000) Hydrolysisesterification Esterification completed at 99% (1) Short reaction time (1) High amount of solvent(2) High esterification percentage (2) Purification by washes

(3) By-product generatedHaas et al. (2003) Hydrolysisesterification High level of esterification (1) Low amount of solvent (1) Purification by washes

(2) Needs two esterifications

(2) No by-product (3) Long reaction time



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The main drawback of the method is the formation ofsodium sulfate in large amounts when acid is added tothe soapstock alkaline solution. This by-product can leadto high disposal costs.

Splitting soapstock with a strong acid (discussed later) isan efficient method for converting FFA to FAMEs without

formation of sodium sulfate as by-product. The addition ofacid to soapstock separates the mixture into two layers.The organic layer is mainly composed of FFA, acylglyce-rols, pigments and other lipophilic materials. In order tosignificantly reduce the content of FFA in the organiclayer, a saponification step prior to the addition of acid iscarried out. This decreases the FFA content to >5% andis further reduced to 0.2% when a second esterification stepis carried out (Haas et al., 2003a). Without saponification,the acid catalyzed method was unsuccessful for the esterifi-cation process resulting in 15% of FA remaining in the oilafter 14 h (Haas et al., 2003a). It was found that varyingthe proportion of FFA:methanol:acid to 1:1.8:0.17 was

beneficial in comparison to the previous study (Haaset al., 2000). Conversion of soapstock into acid oil wateris one of the best methods to use since it has a high conver-sion ratio, low solvent requirement and does not generatesolid sodium sulfate in the product. Sodium sulfate is stillcreated but it dissolves with the incorporation of acidand is removed with the water layer. A similar approachand recovery of methyl esters has also been reported byMarin, Mateos, and Mateos (2003).

The conversion of FA into alkyl fatty acid esters by anenzymatic process has also been investigated. This route isthe least efficient. Two research groups have found that for

an initial mixture of soybean oil deodorizer distillate, theconversion was approximately 63% (Haas & Scott, 1996;Tuter et al., 2004) and using a mixture of corn oil deodor-izer distillate, the conversion was found to be approxi-mately 50% (Tuter et al., 2004).

Using methanol with a catalyst, at a temperature of 80200 C and a pressure higher than 17 atm, fatty acids areconvert to their esters (Luxem & Troy, 2004a, 2004b),but this still does not significantly improve upon themethod developed by Haas, Scott, Michalski, and Runyon(2003b).

4.3. Drilling fluids

Drilling fluids are mainly water-based or oil-based. Oilbased drilling fluids are essentially constituted of an oilphase generally comprised of diesel mineral oil, esters, n-alkanes and olefins, and an aqueous dispersed phase com-prised of water, brine and alcohol. The remainder consistsof organophilic clay, calcium chloride, brine, surfactantsand weighting additives (copolymers and modified asphaltsthat control the rheological properties) (Quintero, 2002).Water based drilling fluids are comprised of water, organo-philic clay as a weighting agent and additives to give thedesired properties. Although water-based drilling fluid is

more environmentally friendly, it has major disadvantages

compared to oil based drilling fluids. Water-based drillingfluid is generally less stable at higher temperatures andosmosis of water into the drilling formation causesborehole destabilization and corrosion of the drillingapparatus.

Oil-based drilling fluids are rich in non-degradable aro-

matic components and are very toxic for the environment,especially when used in offshore drilling where it is difficultto remove all the drilling mud from the cuttings ( Durrieu,Zurdo, Rabion, Fraisse, & Guillerme, 2003; Goncalves, DeOliveira, & Aragao, 2004).

There is limited literature available evaluating the use ofsoapstock and their derivatives in drilling fluid prepara-tions, and to our knowledge, no literature is available onthe utilization of deodorizer distillate in drilling fluid prep-arations. A possible reason for this could be that currentresearch focuses on the recovery of tocopherols and sterolsfrom deodorizer distillate, as already discussed in thisreview. Most research groups investigating the use of soap-

stock in drilling fluid preparations are based in EasternEurope and Russia, and focus on the use of cottonseedwhich is their domestic crop. The majority of work dis-cussed in this section involves the use of soapstock or soap-stock derivatives as additives to improve viscosity orrheological properties of the preparation. Typically, soap-stocks are distilled and fatty acids are added to the drillingmud in concentrations varying from 2% to 25% (wt basis)(Kendis, Zakolodyazhnyi, & Roshchupkin, 1980; Lesh-chinskij & Davidenko, 1984; Mironenko, Kuksov, Parpiev,& Makhmudov, 1989; Motyleva et al., 1982; Zaionts et al.,1970). It is claimed that improvement of the adhesive and

stability properties of the lubricant can be achieved viaaddition of hydrons from the distillation of fatty acids.Later on, it was found (Khasanov et al., 1988) that opti-mum results were achieved by adding hydrons in a propor-tion of 15% to 30% (mass). It has also been reported thatthe overall structural properties of commercial water-basedwell drilling fluids can be enhanced by addition of soap-stock (Klimashkin, Polyakov, Khashimov, Mamadzhanov,& Khodzhaeva, 1984), sulfate soap (Kendis et al., 1980)and lubricating additives (Motyleva et al., 1982). Otherresearch groups have utilized derivatives of soapstock asdrilling fluid additives (Aronova, Zainutdinov, Sataev, &Akhmedov, 1977) and evaluated the use of polyethyleneglycol monoesters of fatty acids, recovered from cottonseedsoapstock, as a surfactant for clay based drilling fluids. Itwas found that at the level used (0.25% wt basis), the soap-stock additive was able to reduce both viscosity and shearstress. However, it has a tendency to form soaps in analkali medium which is a concern as most drilling fluidsare alkali in nature.

Literature on the use of soapstock and soapstock deriv-atives in drilling fluid compositions is focused on cotton-seed and castor oil, other oil sources have yet to beevaluated. The existing literature was published between1970 and 1989 and the research was mainly conducted in

Russia, where cottonseed and castor are readily available.



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Therefore, it is necessary to investigate soapstock anddeodorizer distillates from other seed sources such as lin-seed and canola, which are rich in free fatty acids. Theuse of such a cheap feedstock in conjunction with an invertemulsion or a synthetic base emulsion could decrease theeconomic burden and thus increase the use of these envi-

ronment friendly bases.However, the use of soapstock has many shortcomings.First, the ester based oil formulations currently availablecontain mostly C12C16 fatty acids with limited C18 fattyacids and have high pour points. Any addition or substitu-tion of long chain saturated fatty acids, which are knownto impart high melting points, will lead to higher pourpoints (Mueller et al., 1999). For these reasons, the use ofcanola and flax soapstock and deodorizer distillate in thedrilling fluid compositions could lead to several problems.As reported in the literature, fatty acid content of soap-stock and deodorizer distillate is a reflection of the parentoil composition (Dowd, 1998). In addition, canola and lin-

seed oils consist mainly of long chain C18 fatty acids,which are detrimental to the pour point. The high content($80%) of unsaturated fatty acids in canola and linseed($90%) result in them having lower melting points thantheir saturated counterparts. This could potentially lessenthe problem of pour point but introduce the problem ofoxidative instability. Oxidation which triggers the break-down of the carbon chain structure increases with theincrease of the number of double bonds and could leadto alterations in the rheological properties of the drillingfluid if it occurs to an appreciable extent.

Many additives are utilized in the production of drilling

fluid to impart desired physical properties. There is poten-tial for utilization of fatty acids obtained from soapstocksand deodorizer distillates to synthesize additives to replaceexisting additives that confer toxicity to the final formula-tion. Possible additives that could be synthesized from fattyacids derived from soapstock and deodorizer distillateinclude emulsifiers (fatty acids, fatty acid soaps and fattyacid derivatives), oil wetting agents (fatty acids, crude talloil) and rheology modifiers (fatty acids and polymeric fattyacids) (Ellice, Helmy, & Shumate, 1996). Tapping into suchan economical source of fatty acids for direct use as baseoils in drilling fluid preparations or for the synthesis ofadditives could be commercially profitable. It would there-fore be possible, in addition to economic gains, to addresssome environmental issues surrounding drilling fluids.

Following the strong current trend to develop environ-mentally acceptable replacements for the petroleum andmineral oil based drilling fluids, interest towards the poten-tial of deodorizer distillates and soapstocks of oil refiningas sources of fatty acids is rapidly increasing. Currentresearch is primarily focused on the use of cottonseedand castor soapstocks in the drilling operations. Wastestreams of canola and flaxseed oil refineries have limiteduse and research into their uses in drilling operations haspotential. Further research on these sources will hopefully

provide the drilling industry with economical and environ-

mentally friendly alternatives to petroleum based drillingfluids.

4.4. Specialized applications

This section covers multigrade lubricating greases, gos-

sypol, biosurfactants and derived films. Despite the limitedliterature on derived films, this subject has been added dueto its importance in medical applications.

4.4.1. Multigrade lubricating greases

Multigrade lubricating greases are used in many sectorslike the automotive, machine tools and electrical motor sec-tors. They are semi-solid colloidal compounds basicallycomposed of fluid lubricant and a gelling agent (thickener).The thickener is a soap or a non-soap component thatholds the fluid lubricant and additives together. Soap thick-eners are essentially composed of fatty acid soaps oflithium, calcium, sodium, aluminum or barium. The chem-

ical structure, viscosity and rheological properties of lubri-cating greases have a direct impact on their performance(Adhvaryu, Sung, & Erhan, 2005; Delgado, Valencia,Sanchez, Franco, & Gallegos, 2006; Leslie, 1998). Theuse of fatty acids from soapstock as a thickener for multi-grade lubricating grease has been investigated by El-Adly(2000) and Al-Wakeel and El-Adly (2005). Soapstock istreated with alkali (saponification) to recover fatty acidsprior to their addition to lubricating oil. The addition ofcottonseed soapstock increases the viscosity of the oil andit behaves like a Bingham plastic. This high viscosity isdue to the sodium salt of soapstock which forms crystals

and a fibrous structure (El-Adly, 2000). The chemical andphysical properties of the grease can be modified by addingoil shale filler, which is a dark fine-grained sedimentaryrock composed of layers of compressed clay, silt, or mud.The described method in which new greases are formedthrough addition of fatty acids obtained from soapstockis a cheap process. However, interest in developing thismethodology has been limited to one group of researchers(Al-Wakeel & El-Adly, 2005).

4.4.2. Biosurfactants

Soapstock and post-refinery fatty acids have been used assubstrates for glycolipid (Bednarski, Adamczak, Tomasik,& Plaszczyk, 2004) and rhamnolipid biosynthesis (Benin-casa, Contiero, Manresa, & Moraes, 2002). The aim is tocreate a microbiological surfactant with standard character-istics such as antimicrobial activity, non-toxicity, biode-gradability, capacity of reducing surface and inter-phasetension as well as reduce the production cost. Productionof the rhamnolipid biosurfactant has been achieved usingsunflower oil soapstock. The addition of soapstock andpost-refinery fatty acids as substrates for glycolipids biosyn-thesis by yeast has shown positive effects. A 70% yield hasbeen achieved (Benincasa, Abalos, Oliveira, & Manresa,2004) for the production of rhamnolipid biosurfactants.

Also, production of rhamnolipids has been achieved using



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soybean soapstock with a yield of 75% (Nitschke et al.,2005). Research in this area is economically interesting sinceit does not involve modification of soapstock.

4.4.3. Fatty acid modification diacylglycerols (DAG)

Fatty acids, the main component of deodorizer distil-

lates, are mostly used as additives for animal food, as med-ium-grade soaps for laundry and dry cleaning operations,building maintenance and industrial cleaners, car wash liq-uids, cutting oils, plus food and dairy plant cleaners ( Sonn-tag, 1985).

DAGs are valuable compounds which can be producedfrom the modification of fatty acids from deodorizer distil-late. Some DAGs can prevent body fat accumulation andrecent research has involved investigating their role in theprevention of diabetes (Mori et al., 2005; Nagata & Saito,2006).

DAGs also have application in the food and cosmeticindustries. It has been shown (Lo, Baharin, Tan, & Lai,

2004a; Lo, Baharin, Tan, & Lai, 2004b) that the produc-tion of 1,3-DAG from corn oil and soybean deodorizer dis-tillates is possible by lipase-catalyzed esterification ofglycerol with fatty acids. However, comparison of the costof enzyme versus the cost of final product (DAGs) makesthe method economically unfeasible. Since DAGs are fairlycheap, the literature covering their synthesis from fattyacids is limited.

4.4.4. Derived films

Soapstock derived films from cottonseed and safflowersoapstock have been considered as potential materials for

chemical encapsulation or target delivery in animals andhumans because of their zwitterionic properties (Kuk &Ballew, 1999). Soapstocks are freeze-dried to remove lowboiling point components and solvents. The soapstock isthen submitted to a mechanical pulverization processwhere fine particles are created. These fine particles arethen dissolved in a solvent and cast at room temperature,dried in the atmosphere and separated from the substrate.Applying this simple procedure on cottonseed and saf-flower soapstock (Kuk & Ballew, 1999), produced a filmhaving similar lipid composition (phosphatidylcholine 2535%, phosphatidylethanolamine 1525% and phosphati-dylinositol 510%) as the films used for drug delivery inhumans. The film has also been considered for cosmeticsand dermal drug applications since it is water soluble andforms a mesophase. However, the source of soapstock usedmust be free from gossypol and an extra step is required toremove this toxic compound from cottonseed soapstock.

5. Extraction of valuable components from soapstocks and

deodorizer distillates

5.1. Soapstock

Soapstock has a variety of end uses, such as a nutrient

source for microorganisms, feedstock for chemical reac-

tions, fertilizer ingredient and more importantly fatty acidsource for biodiesel and animal feedstock. This section willdeal with the extraction of fatty acids and gossypol. Asmentioned earlier, gossypol is a toxic substance that needsto be removed from cottonseed soapstock sources prior tobeing used for animal feedstock.

5.1.1. Extraction of fatty acids

Fatty acids are the major component of soapstock, afterwater has been extracted. They represent approximately10% of the soapstock composition on a wet basis. As fattyacids are mainly used in animal feed, the extraction processmust be cheap in order to be justified. These fatty acidrecovery methods include: organic solvent extraction,supercritical fluid extraction (SFE) using CO2 coupled withan enzymatic-based reaction and soapstock splitting usinga mineral acid. These literature methods, however, do notspecify how the waste is disposed of after extraction.

AOCS method G3-53 reports the saponification of soap-stock followed by acidulation as a fatty acid recoverymethod. This method is efficient at recovering the fatty mat-ter but does require 575 mL of petroleum ether for every10 g of soapstock. In order to reduce the amount of solventused, King, Taylor, Snyder, and Holliday (1998) comparedfatty acid material recovered by the G3-53 method and aSFE/SFR (supercritical fluid reaction) method. Table 7shows the result of fatty matter/fatty acid recovery for threesamples of soapstock (soybean (a), soybean (b) and corn(c)) using the above mentioned methods.

It is clear from Table 7 that the two methods result in a

similar average of the recovered matter. Although the SFE/SFR method in this study only required 1.8 mL of solvent,it is not economically viable compared to method G3-53due to the cost of expensive enzymes also used in the pro-cess. Furthermore, the authors have found a significant dif-ference in the percentage of fatty acid recovery between thetwo soybean soapstock samples. As these two samples wereobtained from two different companies, it can be assumedthat one of the samples has been chemically modified ortreated by a different processing method. Slight differencescan occur in terms of concentration of components withinthe same type of soapstock but from Dowds research

Table 7Comparison of fatty matterfatty acid recovery using AOCS method G3/53 and SFE/SFR

Soapstock type G3-53 (%) SFE/SFR (%)

Soybean-based soapstock (a) Average: 31.05 Average: 32.63SD: 0.48 SD: 0.24RSD: 1.55 RSD: 0.72

Soybean-based soapstock (b) Average: 11.03 Average: 12.28SD: 0.02 SD: 0.07RSD: 0.19 RSD: 0.60

Corn oil-based soapstock (c) Average: 38.84 Average: 39.52SD: 0.86 SD: 0.33RSD: 2.22 RSD: 0.84

SD: Standard deviation, RSD: relative standard deviation.



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(Dowd, 1996) which reports the characterization of soap-stock from different regions, it can be seen that significantdifferences in percentage of components is unlikely.

Another way of extracting fatty acids has been devel-oped by Haas, Cichowicz, Jun, and Scott (1995). It requiresthe use of the lipase, Lipozyme I-20, to achieve hydrolysis

of all the TAGs, 70% of the phosphatidylethanolamine and20% of the phosphatidylcholine present in soybean soap-stock samples. The method required a high ratio of organicsolvent to soapstock (8 mL/0.5 g) and an appreciableamount of lipase (50 mg). This method is therefore not rec-ommended for the extraction of a low-value compoundsuch as fatty acids.

In industry, the main process used for fatty acid extrac-tion is called soapstock splitting and is commonly usedbecause it is a low cost, facile method. The general processconsists of soapstock acidulation with sulfuric acid andthen separation of fatty matter from the acid water (Ger-vajio, 2005). However, sulfuric acid is very severe on the

hardware used in the process. The corrosion of pipes canoccur because of the use of concentrated acid, and thishas been addressed in some patents and papers (Asbeck& Walter, 1991; Duff & Segers, 1982; Gadefaix & Klere,1974; Oester, Hall, Zilch, & Anderson, 1997; Piazza &Haas, 1999). To date, this is the most cost-efficient method.

5.1.2. Extraction of gossypol

Gossypol has been a compound of interest since theearly 20th century. It is a polyphenolic compound whichis present in cottonseed soapstock (Fig. 3). It has been

found that acidulated soapstock stored at room tempera-ture for a period of 6 to 10 months decreases gossypol con-tent from 80% to 50%. The authors related the gossypoldecrease with its duration in a basic mixture (Lipstein &Bornstein, 1964b).

There is a method that allows a partial recovery withhigh purity of this minor component from soapstock. Itconsists of acid treatment to hydrolyze covalently bondedgossypol, partitioning of gossypol into an organic phaseand then washing the residue several times. The gossypol

is then concentrated by vacuum distillation and finallycrystallized. This process led to a recovery of approxi-mately 58% gossypol with a purity of 99% after a singlerecrystallization (Dowd & Pelitire, 2001). Gossypol hasanti-tumor (Xu et al., 2005) and anti-viral properties (Kel-ler, Birch, Leach, Tyssen, & Griffith, 2003) and hence

research in this area has attracted great interest.

5.2. Extraction of deodorizer distillate components

Literature on the characterization is mainly based on theidentification and quantification of tocopherol and sterolcontent in deodorizer distillates and deals with their extrac-tion and recovery. Although, there are some isolated pub-lications or patents reported investigating the extraction ofbrassiscasterol from rapeseed distillates, such as Kircherspaper (Kircher & Rosenste, 1973).

5.2.1. Extraction of tocopherols, sterols and squalene

Extensive research has been carried out to determine thebest methods to extract and recover tocopherol from distil-lates. This recovery can be a worthy process because thevegetable oil refining process leads to a significant tocoph-erol loss from the crude oil to the deodorizer distillate. Themajority of tocopherol loss occurs during the deodoriza-tion process (Copeland & Belcher, 2003; Verleyen et al.,2002) where the amount of tocopherol decreases by 23%(Gogolewski, Nogala-Kalucka, & Szeliga, 2000). The neu-tralization and bleaching steps together cause a loss ofapproximately 10.1% of tocopherol (Gogolewski et al.,2000). The four isomers of tocopherol (a, b, c and d)

(Fig. 4) are generally found in the distillate mixture andare also known as vitamin E. Tocopherols must be concen-trated to 60% and free from fatty acids in order to be soldas vitamin E. The presence of squalene (Fig. 5) is not det-rimental to the tocopherols mixture; however the cost ofvitamin E increases with its purity. Squalene is itself animportant commercial compound that is found in the dis-tillates and is generally used in the cosmetic industry as amoisturizer.

These minor components have excellent commercialvalue. The main challenge is to separate them from eachother, especially in the case of the following pairs of com-ponents: tocopherolsqualene, tocopherolfatty acids,tocopherolsterol and sterolsqualene. To separate thesecomponents, the literature proposes these main methods:solvent extraction and crystallization (Lin & Koseoglu,2003; Moreira & Baltanas, 2004), supercritical carbondioxide extraction (SC-CO2) (Buczenko, de Oliveira, &von Meien, 2003; Chang, Chang, Lee, Lin, & Yang,2000; Mendes, Pessoa, Coelho, & Uller, 2005; Mendes, Pes-soa, & Uller, 2002; Mendes, Uller, & Pessoa, 2000; Nage-sha, Manohar, & Sankar, 2004; Wang, Goto, Sasaki, &Hirose, 2004), enzymatic reaction (Nagao et al., 2005;Ramamurthi, Bhirud, & McCurdy, 1991; Shimada et al.,2000; Watanabe, Nagao, Hirota, Kitano, & Shimada,

2004; Weber, Weitkamp, & Mukherjee, 2002) and the

HO

HO

OH

CH(CH 3)2

O HO

O

OH

OH

CH(CH 3)2

Fig. 3. Chemical structure of gossypol.



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molecular distillation process (Martins, Batistella, Maciel-Filho, & Wolf-Maciel, 2006; Martins, Ito, Batistella, &Maciel, 2006). However, all of these methods are at atrialerror stage and there is no literature available as yetthat actually confirms the total separation of all of thesecompounds.

5.2.1.1. Solvent extraction and crystallization. Solventextraction and crystallization are mainly used to recoversterols over tocopherols. This process has the advantage

of not causing tocopherol oxidation and does not use high

pressure, but the amount of solvent required is still veryhigh and the use of such quantities does not lead to an envi-ronmentally friendly process. It is also noted that extrac-tion with solvent requires laborious manipulations.Research in this area is not very extensive due to the lowrecovery and low purity of sterols and tocopherols (More-ira & Baltanas, 2004; Lin & Koseoglu, 2003).

5.2.1.2. Supercritical fluid extraction. Supercritical carbondioxide extraction is a process where carbon dioxide passesthrough a mixture of interest at a certain temperature andpressure until it reaches an extractor. This process is usedbecause supercritical carbon dioxide has a low viscosity,a high diffusivity and a low surface tension that providesselective extraction, fractionation and purification, allow-ing its penetration in micro- and macro-porous materials.The major advantage of this method is the easy post-reac-tion separation of the components by depressurization.Another advantage is the low temperatures used for themajority of the experimentations because carbon dioxidehas a critical temperature of 31.1 C (see Fig. 6). However,the use of high pressure conditions makes the system ener-getically expensive but can be economically viable at a rateof production superior to 25% using conditions of approx-

imately 90 atm and 40 C (Mendes et al., 2002). At these

O

HO

O

HO

O

HO

O

HO

(A)

(B)

(C)

(D)

Fig. 4. Chemical structures of (a) a-tocopherol, (b) b-tocopherol, (c) c-tocopherol and (d) d-tocopherol.

Fig. 5. Chemical structure of squalene.



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specific conditions, only fatty acids are separated from

tocopherol (Mendes et al., 2005). An increase in pressureand temperature increases the oil extraction and tocoph-erol recovery, although different pressuretemperature sys-tems need to be used in order to separate the differentcomponents.

Chang et al. (2000) worked on the separation of severaldistillate components. Their supercritical fluid extractionapparatus had a separation and an extraction unit. Freefatty acids, squalene and tocopherols were recovered inthe extract and the sterols were recovered in the raffinates.The average tocopherol concentration factor was 1.38,which means that the mixture in the extract did not sepa-

rate. However, the author mentioned that with the increaseof CO2 volume, the separation factor can reach 1.7, but thepoor increase in the concentration factor does not justifythe raise in gas volume. The following research groupsfocused on the separation of the problematic pairs usingsynthetic mixtures: Mendes et al. (2000), Mendes et al.(2005), Wang et al. (2004), Nagesha et al. (2004), Rama-murthi et al. (1991), Shimada et al. (2000), Watanabeet al. (2004), Nagao et al. (2005), Weber et al. (2002), Mar-tins, Batistella, et al. (2006), Martins, Ito, et al. (2006),Sumner, Barnicki, and Dolfi (1995), Nagesha, Subrama-nian, and Sankar (2003) and Maza (1992).

Table 8 summarizes the yield and concentration factor(C.F.) of pairs of compounds at different conditions ofpressure (P) and temperature (T) obtained by Mendesand Chang. There are some interesting relationships andconclusions that can be deduced from this table. The bin-ary mixture of tocopherol and squalene cannot be sepa-

rated at low pressure conditions. An acceptableseparation needs a raise in pressure to almost 200 atm(Mendes et al., 2005; Mendes et al., 2000). However, arecovery of 90% and a purity of 60% of a-tocopherol hasbeen achieved using a pressure swing adsorption device,where the adsorption and desorption steps had pressureconditions of 158 and 296 atm, respectively (Wang et al.,2004).

The ternary mixture of tocopherol, fatty acids and squa-lene behaved differently from the tocopherolfatty acidbinary mixture. For the same conditions of pressure (158and 296 atm), the binary mixture had a total separationwhile the ternary mixture did not achieve any separation.

Squalene and stigmasterol mixtures are also very difficultto separate. At low pressure conditions, the yield is lessthan 10% but at higher pressure, the yield is 76% althoughthe compounds do not separate. It is important to note thatlow temperatures were used in these studies. A simulationof the phase equilibrium between the distillate componentsin a CO2 system using the Peng-Robinson Equation ofState (EOS) model showed that at 70 C, the separationfactor between fatty acids and squalene from tocopherolsand sterols in soybean oil deodorizer distillates decreasesas the pressure increases. The partition coefficient (K) ofseveral distillate compounds decreases following this order:

squalene > fatty acids > tocopherols > stigmasterol (Ara-ujo et al., 2001). Eq. (3) shows the Peng-Robinson Equa-tion of state:

P RT

Vm b

aT

V2m 2Vmb b

23

where P is the pressure, R the ideal gas constant, Vm themolar volume, and a and b are parameters related to thepartition parameters between the different species.

Table 8 suggests that the supercritical-CO2 processcould be used for the separation of squalene, fatty acids

0

20

40

60

80

100

120

1161 16 21 26 31 36 41

Temperature C

Pressu

re(atm)

Gas

Supercritical FluidLiquid

Fig. 6. Phase diagram of carbon dioxide.

Table 8Comparison between the yield and concentration factor (C.F.) of pairs of compounds and the different conditions of pressure (P) and temperature (T) used

Mixture T (C) P (atm) Yield (%) C.F.

Chang et al. (2000) Soybean deodorizer distillate 90 top 70 bottom 306 83.6 1.38Mendes et al. (2000) 50% a-Tocopherol50% squalene 80 148 30.0 1.23

10% a-Tocopherol20% squalene70% fatty acids 39 89.0 34.6 a-Tocopherolsqualene: 16.780 148 49.1 a-Tocopherolsqualene: 1.8039 89.0 34.6 a-TocopherolFA: 0.5780 148 49.1 a-TocopherolFA: 1.03

Mendes et al. (2005) TocopherolFA 40 89.0 93.1 InfiniteTocopherolsqualene 40 345 91.0 55.4Tocopherolstigmasterol 40 345 94.0 104Squalenestigmasterol 40 148 76.1 1.00

Squalenestigmasterol 40 89.0 9.20 8.60



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and tocopherols. In order to enhance the squalene, fattyacids and tocopherols separation, deodorizer distillate mix-tures should be processed several times in supercritical-CO2at different temperature and pressure conditions. However,there is no data reported regarding the reaction time of themixture and this makes it impossible to estimate the oper-

ational cost. The major advantage of this method is thetotal removal of free fatty acids from the mixture.Other methodologies have been looked at but were

unsuccessful for the separation of different pairs of compo-nents. An attempt at using similar methodology to Mendeset al. (2000) and Mendes et al. (2005) but using liquid gaspetroleum instead of carbon dioxide did not change thepoor concentration factor between the critical pairs ofcomponents (Buczenko et al., 2003). Another methodologywas developed to focus more specifically on the conversionof FFAs into fatty acid butyl esters (FABEs) (Nageshaet al., 2004). The authors (Nagesha et al., 2004) used immo-bilized Mucor miehei lipase in supercritical carbon dioxide

at high pressure and obtained a maximum recovery of 88%and a FABE purity of 95%.

5.2.1.3. Enzymatic reaction. Enzymatic reactions are basedon the principle of using enzymes for the conversion of aclass of components into a different class in order to modifythe chemical or physical characteristics of the original com-pound. The utilization of enzymes permits the concentra-tion of tocopherols from the distillates by convertingsterols to steryl esters, acylglycerols to free fatty acidsand free fatty acids to fatty acid methyl esters (FAMEs).It is then easier to separate the components that have sim-

ilar molecular weight by distillation. From published liter-ature, it can be seen that the main disadvantages of theprocess are the numerous parameters such as moisture con-tent, enzyme concentration, time, temperature and ratio ofthe reactants (Ramamurthi et al., 1991). The optimal con-ditions for these reactions have yet to be determined.

Distillation of the deodorizer distillate mixture allowsfor the removal of high boiling point components such asfatty acid steryl esters, DAGs and TAGs. However, thisdistillation step can be carried out after the esterificationof sterols and FFA, without significantly affecting theirconversion into steryl esters and FAMEs.

The conversion of FFAs to FAMEs is an important stepin the concentration and purification of tocopherols. If thisstep is omitted, the separation of FFA and tocopherols bydistillation cannot be achieved due to their similar boilingpoints (Shimada et al., 2000). Furthermore, methanol usedfor the conversion of FFA to FAMEs inhibits sterol ester-ification. To avoid this problem, a lipase can be used topromote the esterification of sterols with free fatty acidsand hydrolysis of acylglycerols should be carried out beforeesterification of the free fatty acids. The different compo-nents are then successfully separated by short path distilla-tion since their boiling points are now sufficiently different.Two research groups (Nagao et al., 2005; Watanabe et al.,

2004) have applied this procedure using Candida lipase for

the purification of tocopherol in soy oil deodorizer distil-lates. Both groups report a tocopherol purity of approxi-mately 75% and a yield of approximately 88%. Theconversion of sterols into their esters was 97% and theirrecovery was approximately 86%. One of the main disad-vantages of this method is that the free fatty acids are

not completely separated from the tocopherols. Thismethod is also a time consuming process that requires ahigh ratio of solvent to lipase, both of which are expensive.

Weber et al. (2002) has also reported the use of lipase forthe conversion of sterols into steryl esters leading to ahigher degree of purity (90%), however the methodologyis more complex and involves deacidification, flash chro-matography and solvent fractionation.

5.2.1.4. Molecular distillation. Molecular distillation allowsfor the separation of components by short exposure of amixture to an elevated temperature under high vacuumconditions. Saponification of the distillate prior to molecu-

lar distillation raises the tocopherol recovery from 73.4% to85.8% (Martins, Ito, et al., 2006). The major disadvantagein this case is the residual free fatty acids in the tocopherolmixture despite their significant boiling point difference(Martins, Batistella, et al., 2006; Martins, Ito, et al.,2006). This process is the most time efficient and econom-ical method, however high purity of sterols or tocopherolscannot be achieved due to the similar boiling points of thecomponents.

5.2.1.5. Other methods. There have also been limited litera-ture reported on the following methods: (1) permeation of

tocopherols from deodorizer distillates using a non-porousdenser polymeric membrane (Nagesha et al., 2003), and (2)concentration of tocopherols and sterols by addition ofmelted deodorizer distillates to a solution of urea and alco-hol which separate fatty acids from the mixture (Maza,1992). Since these methods do not present any advantagesover the main methods, they will not be discussed further.

6. Conclusion

Literature on the characterization of soapstock anddeodorizer distillates is very limited and only a few typesof raw materials have been investigated. The bulk of theresearch carried out on soapstocks focuses on fatty acidutilization or transformation and research carried out ondeodorizer distillates focuses on tocopherol extraction.However, economical information is missing for the extrac-tion of tocopherols from distillates.

The majority of literature found on the transformationof fatty acids from soapstock concerns principally biodie-sel. Several methods that have been developed for the con-version of fatty acids into FAMEs show favorable results.Unfortunately, no economical viability has been assessedand no comparison between the methods has been carriedout. This is critical missing information if the production of

biodiesel from seed oil wastes is to be upgraded to an



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industrial scale. Fatty acids from deodorizer distillates havenot been considered for the production of biodiesel. At thispoint, for comparison purposes, it might be legitimate totry to make FAMEs from the distillates using the methodsapplied for the production of FAMEs from soapstock.

Except for the direct use of soapstock in animal feeds, a

limited number of papers have been published on this sub-ject. Other utilization and transformations of the by-prod-uct are still at a primary stage. Although, these applicationsare original and so far successful, more research should becarried out for a full exploitation of soapstock and deodor-izer distillate by-products.

Acknowledgements

The financial support of Alberta Crop Industry Devel-opment Fund, NSERC, Bunge Corp., AVAC Ltd. and Ar-cher Daniels Midland is gratefully acknowledged. Wewould also like to thank Drs. Xiaohua Kong and HayleyWan for editing help.

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Soapstock and Deodorizer Distillates From North American