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ceConjugated Linoleic Acid (CLA) Formation inEdible Oils by Photoisomerization: A ReviewRahul Reddy Gangidi and Belur Ramaswamy Lokesh

Abstract: Conjugated linoleic acid (CLA) that is commonly found in dairy and ruminant fats, is geometrical andpositional isomer of linoleic acid (LA). Edible oils are not good sources of CLA. Attempts have been made to generateCLA in edible oils through photoisomerization procedures. CLA isomers have several proven health benefits. Thisarticle reviews procedures for producing CLA containing edible oils by photoisomerization approach and applicationsof photoisomerized oils for food uses. The article reviews (1) the photoisomerized production of CLA containing oilson lab scale, with customized equipment, at pilot plant scale; (2) the effects of iodine content, photoisomerization time,refining, interference from minor components of oils, efficacy of different edible oils containing LA, interference fromantioxidants; (3) the chemical kinetics, oxidative stability; and (4) photoisomerized oils for frying oils and as dryingoils.The review also briefly covers methods of measurement of CLA.

Keywords: CLA, iodine, photoisomerization

IntroductionThe cis-9, trans-11 conjugated linoleic acid (CLA) is the princi-

pal CLA in dairy and meat products and is found mainly in phos-pholipids fraction (Ha and others 1987; Chin and others 1992).The amount of cis-9, trans-11 CLA in meat varies from 0.17 to0.65 g for 100 g of meat-fat whereas the amount of linoleic acid(LA) found in meat is 0.6 to 1.37 g (Fritsche and Fritsche 1998).

The CLA has positive health effects, such as acting as anti-carcinogen (Ip and others 1991), antimutagen (Pariza and others1979), protecting against immune-induced muscle wasting (Cookand others 1993; Miller and others 1994), decreasing body fat andincreasing lean body mass (Chin and others 1994; Park and others1997), and decreasing atheroscelorosis (Lee and others 1994; Ni-colosi and others 1997). Photoisomerized soybean oil that contains25% total CLA of which 70% is contributed by trans, trans CLAisomers, 25% by cis, trans CLA isomers, were found to decreaseserum cholesterol and serum low density lipoprotein cholesterol,lowered lipid content, decreased liver weight in obese rats (Gilbertand others 2011).

Human intake of CLA from dairy lipids and meat fats is one-tenth of the needed 3 g/d minimum value extrapolated fromanimal studies for beneficial effects (Ip and others 1994; Ma andothers 1999). This is not possible to achieve from existing dietarysources for CLA. This underscores the need for increasing CLAisomers by diversifying the sources for CLA, including CLA con-taining edible oils and fats. Photoisomerization process could beutilized to produce CLA in edible vegetable oils and fats, whichis economical and can be used to prepare CLA rich oils in largeamounts.

CLA—in relation to LACLA is a group of positional and geometrical isomers of oc-

tadecadienoic acid (LA) having a conjugated double-bond system(─C═C─C═C─) starting at carbon 9, 10, or 11. All configura-

MS 20131612 Submitted 11/5/2013, Accepted 2/11/2014. Authors are withLipid Science and Traditional Foods Dept., CSIR Central Food Technological ResearchInst. (CFTRI), Mysore, Karnataka [570020], India. Direct inquiries to authorGangidi (E-mail: gangidirr@gmail.com).

tions of cis-trans, trans-cis, cis-cis and trans-trans are possible in eachof the 3 positional systems (Ha and others 1987).

Conventional LA (─C═C─C─C═C─) is found mainly inplants. LA is an essential fatty acid for humans, as they cannotsynthesize a fatty acid with double bond beyond carbon 9. For thisreason cis-9, trans-11 CLA could be synthesized by humans fromdietary vaccenic acid (trans-11 C18:1 oleic acid), and not trans-10,cis-12 CLA isomer, and will have to be obtained from dietary sup-plements. Trans-10, cis-12 CLA is also found to have health benefitsin terms of decreasing body fat (Dilzer and Park 2012). Animal andcell line studies indicated that 3 g/d/person of CLA consumptionis needed for optimum health benefits (Ip and others 1994). Ge-ometrical isomers of LAs were found to have similar metabolismto that of normal n-6 LA. However geometrical and positionalisomers of LA, including conjugated LA, do not have essentialfatty acid functions as that provided by LA (Coots 1994). Inst. ofMedicine of USA recommends daily intake of approximately 10to 17 g of LA and 1 to 1.7 g of alpha-linolenic acid per person(Dietary Reference Intakes: Macronutrients, www.iom.edu). The3 g of CLA for day/person should be in addition to 10 to 17g/d/person for LA.

Trans fatty acids have 2 hydrogens on the opposite sides of theadjacent carbons (Guidelines on Nutritional Labelling, CAC/GL1985; Wong 1989), while cis fatty acids have hydrogens on thesame side of the carbon–carbon double bond. Trans fatty acidfound in partially hydrogenated fats, is mostly elaidic acid (trans-9,C18:1) with a single trans double bond (─C─C═C─C─), CLAhas conjugated carbon–carbon double bonds (─C═C─C═C─),in either cis or trans geometry.

Codex Alimentarius states “ . . . . . . . . . . . . trans fatty acids aredefined as all the geometrical isomers of monounsaturated andpolyunsaturated fatty acids having nonconjugated, interruptedby at least 1 methylene group, carbon–carbon double bonds inthe trans configuration” (Guidelines on Nutritional Labelling,CAC/GL 2 (1985), last modified in 2012), while Food and DrugAdministration (FDA) of United States of America (US) defines“Trans fat” or “trans” as “ . . . . . . . . . .the sum of all unsaturatedfatty acids that contain 1 or more isolated (that is, nonconju-gated) double bonds in a trans configuration . . . . . . . . . . (USGovernment Code of Federal regulations (CFR) 101.9, currenton May 2013).”

C© 2014 Institute of Food Technologists R©doi: 10.1111/1750-3841.12449 Vol. 79, Nr. 5, 2014 � Journal of Food Science R781Further reproduction without permission is prohibited

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CLA formation by photoisomerization . . .

Food safety standards authority of India (FSSAI) under Min-istry of Health and Family Welfare, Government of India has notdefined trans fat and hence currently definition of trans fat fromCODEX is followed in India. FSSAI regulations for trans fattyacids specifies that its content should be restricted to less than10% in partially hydrogenated fats (vanaspati), bakery shortening,and bakery and industrial margarine ( Food Safety and StandardsAuthority of India 2011).

The cis-9, trans-11 CLA and trans-10, cis-12 CLA isomers werefound to be safe for human consumption (Pariza 2004). Details ofhealth benefits and mechanisms of CLA isomers biological actionare presented in other literature (Pariza and others 2001; Rocheand others 2001; Belury 2002; Borzelleca and others 2004; Pariza2004; Kelley and others 2007; Dilzer and Park 2012) and is beyondthe scope of current article.

Production of CLA—biochemical and chemical proceduresIn addition to photoisomerization formation of CLA from LA,

CLA was produced from LA by isomerase enzyme from Bu-tyrivibrio fibrisolvens (Kepler and Tove 1969), lactobacillus (Parizaand Yang 1999) species; extraction of trans-10, cis-12 CLA fromchilopsis seed oil (Hopkins and Chisolm 1964), chemical syn-thesis by dehydration of hydroxy fatty acids, such as ricinoleicacid (Grummitt and Marsh 1953; Gunstone and Said 1971),bromination/dehydrobromination of oleic acid (Schmidt andLehmann 1950), reduction of polyunsaturated fatty acids, such asalpha-eleostearic acid (9-cis, 11-trans, 13-trans-octadecatrienoic acid)(Mikolajczak and Bagby 1965), reduction of mono-acetylenic fattyacids such as santalbic acid/ximenynic acid (11-trans-octadec-9-ynoicacid) (Morris and others 1972; Smith and others 1991; Lie-Ken Jieand others 1996; Lie-Ken-Jie and others 1997), alkali isomeriza-tion of LA (Nichols and others 1951; Berdeaux and others 1998).Detailed commercial procedures of CLA production are beyondthe scope of this article and are presented elsewhere (Reaney andothers 1999). These methods have disadvantages such as low yields,formation of only 1 isomer, requiring extensive chemical transfor-mation (reduction, halogenation/dehydration, fractionation) andfurthermore, in these methods CLA fatty acids are produced ratherthan functional and utilizable CLA triacylglycerides.

Commercial procedures of CLA production are beyond thescope of this article and are presented elsewhere (Reaney andothers 1999). Compared to the reported earlier methods, pho-tosomerization of edible oils can produce CLA isomers in tria-cylglycerides economically, in larger quantities, rapidly, and withsimple approach.

Production of CLA—photoisomerization proceduresIsomers of CLA could be produced from vegetable oils by pho-

toisomerization. Photoisomerization is defined by InternationalUnion of Pure and Applied Chemistry (IUPAC) as “photochem-ical process leading to an isomerization of the substrate, eitherby bond rotation, skeletal rearrangement, or atom- or group-transfer.” In the photoisomerization studies, 80% yield of CLAmethyl esters was produced from LA methyl esters (Canaguierand others 1984; Seki and others 1998), which contained ap-proximately 70% trans, trans CLA isomers, approximately 25% cis,trans CLA isomers, and 5% CLA cis, cis isomers. Gangidi andProctor (2004) used photoisomerization of edible oils to produceCLA. This procedure is simple, requiring no caustic solutions, hightemperatures and high pressures, or intense and tedious chemicalfractionations and extractions or requiring transesterification ofCLA into triacylglycerides. Soybean oil containing approximately

48% to 59% LA was used for producing CLA rich oil by photoiso-merization. In the earlier methods, LA methyl esters (5% to 10%)or vegetable oils, were dissolved in petroleum ether, benzene, orcarbon disulfide and then exposed to a strong light source in thepresence of iodine as a sensitizer (Julliard and others 1987).

CLA production on lab scale. Approximately 0.59% each ofcis-9, trans-11 CLA and trans-10, cis-12 CLA were produced after90 h of irradiation of soybean oil in the presence of 0.33% iodine.Soybean oil was used in native form, molecular iodine (I2) was dis-solved in oil, and no solvents were used. A high-pressure mercurylamp was utilized to photoisomerize the soybean oil in the pres-ence of iodine in a 250 mL beaker keeping the lamp, at a height of45 cm. When the oils samples were not stirred, the low amountsof CLA production was observed. CLA isomers were not pro-duced in the absence of iodine, or in the absence of light or both.The lipid oxidation products as determined by attenuated totalreflectance-Fourier transform infrared spectroscopy (ATR-FTIR)and 1H NMR were not detected (Gangidi and Proctor 2004).

Customized production of CLA. To further advance earlierwork of Gangidi and Proctor (2004), iodine added to soy oilsamples were placed in customized glassware giving a close contactfor oil with lamp. The glassware consisted of a central space forlamp surrounded by sealed cylindrical space open at the top andwith magnetic stirrer at bottom. The glassware also has allowancefor water jacket to control and maintain temperature of oil.

Utilizing this glassware setup and stirring of the oil at 20 to25 °C gave approximately 50% conversion of LA into conjugatedLA. Approximately 74% of the CLA isomers were trans, trans con-figuration. A 3.5% of cis, trans CLA isomers were also formedand the concentration of these isomers was significantly higherthan that found in animal products (Jain and Proctor 2006). A0.15% iodine gave higher total CLA when compared to 0.1%or 0.25% iodine concentration. In addition, 0.1% iodine contentgave higher cis-9, trans-11 CLA and trans-10, cis-12 CLA duringthe early stages of photoisomerization. No significant oleic acidpeak reduction was observed suggesting possible minimal conver-sion of cis oleic acid to trans elaidic acid. However, the minimalconversion of cis oleic acid to trans elaidic acid needs to be con-firmed. Lipid oxidation products were not detected as determinedby gas chromatography-mass spectrometry (GC-MS) headspaceanalysis, ATR-FTIR, 1H NMR. In addition, photoisomerizedsoy oil with iodine was bleached with clay to remove iodine, andresulting bleached oil was comparable with that of the originaledible oil, with higher CLA concentration.

CLA content was found to increase by approximately 15%,when iodine (0.35%) containing soybean oil was 1st added, fol-lowed by photoisomerization for 12 h, and later iodine wasremoved by adding 5% magnesol (an iodine and polar materialadsorbent). Another dose of iodine (0.35%) added and then pho-toisomerized for further 12 h resulted in a higher CLA contentof approximately 17.5%. CLA content (approximately 25%) wasalso found to increase by 67% when magnesol adsorbent alonewithout addition of iodine was utilized to remove iodine (Yettellaand others 2013).

More rapid and near complete conversion of LA into CLAwas observed, when edible oil is solubilized in a nonpolar solventand then photoisomerized. A 11% soybean oil in hexane with0.04% iodine in mixture, resulted in 99% conjugation in approxi-mately 8 h photoisomerization at 70 to 80 °C with high pressuresodium vapor lamp. Approximately 5%, 23%, and 39% were cis-9,trans-11 CLA; trans-10, cis-12 CLA; and trans, trans CLA isomers,respectively (Chintareddy and others 2012). However, this type of

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photoismerization may result in residual solvent in CLA enrichedsoybean oil, which needs to be removed.

CLA production on pilot plant scale. To solve the prob-lems of low surface area to volume ratio, longer photoisomeriza-tion times and batch wise operation for CLA production in earlierstudies, an illuminated laminar flow unit (ILFU) (Jain and Proc-tor 2008) was built at Univ. of Arkansas, Dept. of Food Science.ILFU consisted of 2 flat glass plates separated by 0.5 cm or othercustomized distance. The oil is made to flow through ILFU ormade static between the sealed plates. The ILFU is exposed tomedium pressure mercury lamp and controlled temperature con-ditions. When the temperature was approximately 50 °C, 0.33%iodine and distance between the plates was 0.5 cm, a maximumtotal CLA isomers of approximately 22%, and 2.7% cis, trans CLAisomers were formed within 12-h exposure time instead of 144 hrequired in earlier setup. Conjugated linolenic acids were alsofound to have health benefits (Kohno and others 2004) and mayalso be produced during the photoisomerization of edible oils.

Surface area of exposure is higher in ILFU. Static mode gavehigher concentrations of CLA, when compared to continuousmode suggesting a finite exposure time required for the light,iodine, and double bonds to react for CLA formation. In addi-tion, placing a reflective surface increased the CLA production,suggesting direct relation between light flux or light intensityand CLA production. The produced cis-9, trans-11 CLA, andtotal CLA isomers in soybean oil were found approximately 14times and 350 times higher, respectively, when compared to thosefound in dairy/milk products or animal products (Jain and Proctor2008).

Photoisomerization differs from photoxidation. In pho-toisomerization, excited photosensitizers, such as iodine molecule(I2) absorbs light (hv) and then cleaves into iodine radicals (I•) andthen abstracts hydrogen radical (H•) from lipid molecule (LH) toproduce a lipid free radical (L•) (Yettella and others 2011). In thisprocess, double bond is rearranged to a more resonance-stabilizedform such that conjugated isomer (LHc) of the fatty acid is pro-duced. Molecular iodine is utilized in the photoisomerization pro-cedure. Iodine is one of the most common elements available inabundance in sea water (atomic number 53, atomic weight 126.9,molecular formula is I2; absorbance is 521 nm). Molecular iodineis utilized in the photoisomerization procedure.

I2 + hv → I • +I •

LH + I • → L • +HI → LHc + I •

In photoxidation (Wong 1989), excited triplet sensitizer3Sen∗ abstracts either a hydrogen radical (H•) or electron(e−) from the lipid molecule (LH) to initiate a chain reac-tion; or excited triplet transfers energy to ground state atmo-spheric triplet oxygen (3O2) to produce excited singlet oxygen(1O2), which then reacts with lipids to produce hydroperox-ide (LOOH). Excited triplet sensitizer (3Sen∗) is produced whenthe ground state singlet sensitizer (1Sen) is exposed to light (hv).

1Sen + hv → 3Sen∗

3Sen∗ + 3O2 → 1Sen+1O2

LH+1O2 → LOOH(or)

1Sen + hv → 3Sen∗

3Sen∗ + LH → Sen-H + L •

Time taken for photoisomerization reaction could be mini-mized by increasing/optimizing molecular interaction between

free iodine and double bonds and light for faster production ofCLA content. The photoismerization can be performed done atatmopsheric pressures; and temperatures between 20 and 55 °Care often utilized. Currently, amount of light energy irradiated andthe wavelength on the sample needs to be standardized. Some ofthe lamps utilized for photoisomerization are high-pressure mer-cury lamps (Seki and others 1998; Gangidi and Proctor 2004),medium pressure mercury lamps (Jain and Proctor 2006), xenonlamps (Julliard and others 1987), high-pressure and low-pressuresodium lamps, and tungsten halogen lamps (Chintareddy and oth-ers 2012). A xenon lamp was modified by placing a water containerbetween xenon lamp and sample to absorb UV radiation (Julliardand others 1987). Typically mercury lamps contain yellow filters toconcentrate UV lights and these need to be removed for optimiumCLA production (Gangidi and Proctor 2004).

Butene, an alkene, has similar double bond to that found infatty acids. Less than 3% of cis butene was converted to transbutene (Back and Cvetanovic 1963) when it was irradiated withvisible light at 501 nm in the presence of iodine as photosensi-tizer. This study also suggests that the amount of monounsaturatedtrans fats produced by photoisomerization from naturally occuringcis fats in the oil may be negligible (Jain and Proctor 2006) andalso suggests that free radical mediated 1,4 butadiene structure maybe required for maximum transformation of LA to conjugatedLA. This also indicates that the amount of monounsaturated fattyacids with trans geometry in any given photoisomerized edible oil,with approximately 20% oleic acid (Jain and Proctor 2006) willbe less than recommended 1% trans fat limit of the total calorificenergy intake/day/person, set by WHO. This is also less thanIndia’s FSSAI 10% trans fatty acid limit. Therefore, photoi-somerized oil with CLA can be consumed. However, theamount of trans monounsaturated fatty acids produced need to beconfirmed.

Effect of photoisomerization on other edible oils con-taining LA content. LA (predominantly cis-9, cis-12 C18:2) ispresent in edible oils at following proportions: 67.8% to 83.2% insafflower oil, 48% to 59% in soybean oil, 48.3% to 74% in sun-flower oil, 10% to 24% in mustard oil, 15% to 30% in rapeseedoil (low erucic acid), 36.9% to 47.9% in sesame oil, 9% to 12% inpalm oil, 12% to 43% in ground nut oil, 3.5% to 21% in olive oil,1% to 2.5% in coconut oil, 2% in butter, 46.7% to 58.2% in cottonseed oil, 56% in wheat germ oil, 29% to 41% in rice bran oil, 34%to 65.6% in corn oil (Codex Standard for named Vegetable Oils,CODEX STAN 210, 1999).

Safflower oil, soy oil, corn oil, sunflower oil, flaxseed oils weretested producing CLA from LA by photoisomerization proce-dure (Gammill and others 2010). Safflower oil produced highestamounts of total CLA isomers, when the ILFU was utilized, fol-lowed by soy oil. ILFU increased the surface area to volume of lightexposure. Flaxseed oil (linseed oil) contained significant amountsof phospholipids that could inhibit CLA production. Sunfloweroil had the turbidity owing to waxes and sterols that could inhibitCLA production. Lutein/carotenoids, tocopherols also affectedthe CLA production. Refining of these oils before subjecting tophotoisomerization yielded slightly higher amounts of CLA. Soyoil and safflower oil were found to be best edible oils for CLA pro-duction. While sunflower oil did not produce any CLA, flaxseedoil and corn oil produced lesser than expected amounts of CLA.Therefore, CLA production is not only dependent on LA contentbut also on interference from minor components present in edi-ble oils that may not be removed by alkali refining (Gammill andothers 2010).

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Interference of minor components in oil on CLA pro-duction. Minor components such as peroxides, free fatty acids,tocopherols, lutein/carotenoids, phospholipids all affected CLAproduction. Peroxide value of greater than 0.8 in the oil decreasedCLA production in a dose-dependent manner. Tocopherols overand above 1400 ppm decreased CLA production. Free fatty acidsabove 1200 ppm decreased CLA production. Lutein at levels above31 ppm decreased CLA production. Phospholipids above 500 ppmin the oil decreased CLA production (Tokle and others 2009).Refining the edible oil with magnesol, an adsorbent that removespolar components like peroxides, free fatty acids, prior to photoi-somerization, increased the CLA yields (Yettella and others 2013).

Effect of refining/processing of oil on CLA productionby photoisomerization. The cis, trans CLA isomer and trans,cis CLA isomers contents of crude soy oil, alkali-refined soy oil,alkali-refined and bleached soy oil; and alkali-refined, bleachedand deodorized (RBD) soy oil were found to be 0.2%, 1.7%,2.8%, and 4.3%, respectively.

Total CLA content of crude soy oil, alkali-refined soy beanoil, alkali-refined and bleached oil, and alkali-refined, bleachedand deodorized oil were found to be 0.2%, 6.4%, 10.3%, and16.3%, respectively. Cis, trans/trans, cis CLA, and total CLA forRBD soybean oil was found to be 21 times and 81 times higher,respectively, compared to crude soy oil. A 0.35% of iodine, 12 hand 47 °C were utilized in the study (Jain and others 2008).

Components present in crude oil such as moisture, free fattyacids, hydratable and nonhydratable phospholipids, natural color-ing compounds, such as carotenoids, xanthophylls, chlorophyll af-fected CLA production in crude soy oil (Jain and others 2008). Theinterfering crude edible oil components can be removed by refin-ing which includes neutralizing/deacidifying by alkali, bleaching,deodorization (RBD). Alkali refining, which includes degum-mimg and phosphoric acid degumming, removes free fatty acid,hydratable and nonhydratable phospholipids. Bleaching removeschromophores/coloring compounds of carotenoids, xanthophyllsand chlorophylls, polar compounds such as peroxides. Deodoriza-tion further removes steam volatile odor and nontriacylglyceridematerials from oils, such as residual free fatty acids, tocopherols,and other antioxidants (Nawar 1996). Moisture varied between0.01% and 0.1% and was lowest for RBD soybean oil and highestfor the crude soy oil. Titratable acidity, an indicator of free fattyacids, ranged from 0.1% to 0.7% and decreased with increasingrefining from crude to RBD oils. Peroxide values ranged from0.2 to 1.2 meq of O2/kg for crude to RBD soybean oil. Totaltocopherol content remained the same for crude, alkali-refined,alkali-refined, and bleached soybean oil but decreased for RBDsoybean oil, probably due to losses during deodorization and CLAlevels ranged from 0.2% to 16.3% (Jain and others 2008).

Oxidative stability of CLA-enriched edible oils. CLA wasfound to be marginally more prone to oxidation when comparedto LA. After 3 d of storage, headspace oxygen content reducedfrom 21% to 11.5% with 0% CLA; to 9.5% oxygen content in 10%and 20% CLA containing soy oil samples, when stored at 65 °C(Yettella and others 2012). Oxidative stability of CLA isomers wasless than that of the LA (Zhang and Chen 1997).

Kinetics of CLA production. Formation of cis-9, trans-11CLA and trans-10, cis-12 CLA from LA (cis-9, cis-12 18:2) followed1st order kinetics with a rate constant of ktct of 2.75 × 10−6/swith the production total cis, trans CLA (Ctct) at a given time, “t”determined by Ln(Ctct) = –Ln(C0) + ktct × t (Jain and Proctor2007a). Initial concentration of CLA in original edible oil sampleis zero, C0 = 0. The concentration of “intermediary” cis, trans

CLA due to photoisomerization of LA to cis, trans CLA as wellas due to formation of trans, trans CLA from cis, trans CLA. Rateconstant can be utilized to determine CLA concentration at anypoint of time during photoisomerization.

Disappearance of cis-9, cis-12 LA was 2nd order reaction with arate constant, kL of 9.01 × 10−7L/(mol.s) and the concentrationof LA (At) at any point of time can be determined by At = (A0)/(1 + A0kLt), where A0 is initial LA concentration. Disappearanceof LA is due to formation of cis, trans CLA and then to formationof trans, trans CLA from cis, trans CLA (Jain and Proctor 2007a).

Formation of trans, trans fatty acids was a zero order reactionwith a rate constant “ktt” of 10.68 × 10−7 mol/(L.s) and theconcentration of trans, trans fatty acid “Ctt” at any given point oftime can be determined by Ctt = ktt × t. A 0.15% iodine wasadded to soy oil and photoisomerized at 22 to 25 °C for 144 h(Jain and Proctor 2007a).

Other ResearchAdditional details of research work on CLA with 4371 arti-

cles are published in various journals between 1979 and July2013, are available in Univ. of Wisconsin (USA) Web site(http://fri.wisc.edu/cla.php). Specific and elaborate details onCLA formation by photoisomerization are presented in bookchapter by Jain and Proctor (2012).

ApplicationsApplication of photoisomerized oil as frying oils. Soy-

bean oil enriched with CLA obtained by photoisomerization wasutilized for frying potato chips. CLA-enriched photoisomerizedsoybean oil was prepared from soy oil containing approximately50% LA by photoisomerizing with 0.1% iodine for 144 h and laterthe iodine is removed by adsorption with bleaching clay (Jain andProctor 2007b). The CLA-enriched photoisomerized soybean oilperformance was similar to that of original soybean oil. However,the product fried in CLA rich oil contained significant amountsof CLA. A cis-9, trans-11 CLA and trans-10, cis-12 CLA contentof oil content in potato chips fried utilizing photoisomerized soyoil was statistically similar to that of original photoisomerized oilof 1.75% each. Similarly, total CLA content of oil/lipid in potatochips fried with photoisomerized soy oil for 175 °C for 3 min wassimilar to that of the original photoisomerized soy oil of 14.75%.Frying temperature of 175 °C, frying time of 3 min, potato chips,potato chip thickness of approximately 60 to 100/100 of an inchdid not affect the CLA content, composition of the CLA-enrichedsoybean oil, oil/lipid content in potato chips fried with CLA en-riched photoisomerized oil. Peroxide values of oil from potatochips and original photoisomerized CLA enriched soybean oilwere same of about 1 meqO2/kg of sample. The appearance ofthe potato chips fried with soybean oil and CLA-enriched (pho-toisomerized) soybean oil were similar. Oil content of all potatochips was approximately 39%.

CLA-enriched soybean oil as drying oil. Conjugated fattyacids containing oil may be utilized as drying oils. CLA containingsoy oil produced by photoisomerization was found to be equal orbetter than linseed oil in drying properties (Chintareddy and others2012).

Conclusions and Future Line of WorkAlthough CLA isomers, in general, were found to have sev-

eral health benefits, more biochemical studies are needed with thephotoisomerized soybean oil to confirm their health benefits andsafety. While safety of cis-9, trans-11 CLA and trans-10, cis-12 CLA

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was established, similar safety studies needs to be conducted forother isomers. Efforts should be made to increase the productionof cis, trans CLA isomers and to minimize the trans, trans CLAisomers in photoisomerized edible oils. Future work needs to beaddressed optimizing conditions for photoisomerization, in termsof wavelength(s), light intensity, photoisomerization time, refin-ing parameters, iodine, solvent concentration, photoisomerizationsetup, nutritive blending for producing CLA rich oil which sat-isfies regulatory parameters for commercial production of CLA.In addition, long-term storage shelf life stability, processed foodsstability for the photoisomerized CLA-enriched oil needs to beevaluated. Photoisomerized soybean oil enriched in CLA has po-tential for a safe, low cost, readily available, and acceptable sourceof health-promoting CLA.

AcknowledgmentsThe authors are very grateful to Council of Scientific and In-

dustrial Research (CSIR), Human Resource Development Group(HRDG), New Delhi for CSIR Research Associateship. They arethankful to Director, CSIR-Central Food Technological ResearchInst. (CFTRI, Mysore); and Head of the Lipid Science and Tra-ditional Foods (LSTF) Dept. (CSIR-CFTRI, Mysore) for theirencouragement and support.

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