.12

Stable andhealthfulfrying oil

for the21st century

This article is by S. P. Kochhat, techni-cal director for Good-Fry

international NY, Research andDeuelotnnent Centre, 48 Chi/tern

Crescent, Earley, Reading RG6 IAN,Eng/mId (phone: 44-118-9261611;

fax: 44-118-9626079; e-mail: good-fry@rocketlnoif.com).

Volume 11 • June 2000 • Inform

Food Technology

fried foods with desirable color, appear-ance, flavor, and texture. During thefrying process, oil is continuously orrepeatedly subjected to temperatures of170-200"C in the presence of air andmoisture. Under these conditions, sever-al changes occur in food, namely, starchgelatinization, protein denaturation,water vaporization, and texturalchanges. In addition, many chemicalreactions rake place in oil during fryingoperations at elevated temperature,which may be grouped into oxidation,polymerization, and hydrolysis. Detailson the chemistry of deep-fat frying aregenerally known.

The detrimental effects of variousminor components, such as free Farryacids, trace metals and partial glyc-erides, which may occur in the frying oilor may migrate from the food productinto the oil, have been reported.

Healthful eating is part of the creed ofour modem lifestyle. These days, a con-siderable number of mainstream con-sumers are becoming aware of healthbenefits of specific food ingredients.Frying oils also are changing owing toconsumer demand for healthful snackproducts and convenience foods.

Most likely, the majority of con-sumers all over the world wiil continueto eat fried foods in the 21st century. Itwould be helpful if the snack industryand the fast-food sectors could offerfood products that are as nutritious aspossible. Traditionally, less-stable liquidoils have been hydrogenated to enhancetheir oxidative stability for deep-fat fry-ing use. However, considerable amountsof trans and positional isomer fatty acidsare formed during hydrogenation, whichhave been described as nutritionallyundesirable. The stability of frying oils issometimes increased by careful blendingof polyunsaturated oils with more satu-rated oils. The natural way of improvingoxidative and flavor stability of fryingoils and fats is by adding natural annex-idarive components and their precursorspresent in the plant kingdom.

The oil or fat used for fryingbecomes pan of the food being fried.The nutritional quality of the frying oilis therefore of great importance withregard to the qualiry of fried foods, suchas potato chips, potato crisps, and friedpellet products. Frying oil quality influ-ences oil absorption and the types of by-products and residues absorbed by friedfood. The development of new, stable,and healthful frying oil for the manu-facture of healthier snack products andconvenience foods in the new centuryhas been considered.

Chemistry of deep-fat fryingDeep-fat frying is a complicated ther-mal-chemical process that produces

Typical frying oils and fatsDuring the past 20 years, the once tra-ditional use of groundnut (peanut) oilfor frying purposes has become rare orspecial. These days, in (he UnitedKingdom and other European coun-tries, alternative vegetable oils, namelyrefined rapeseed oil, lightly hydrogenat-ed rapeseed oil, palm oil/rapeseed oil orsoybean oil blends, and palm olein or"super" oleins are used. Owing toregional choice and for special productapplications, animal fats (beef tallow orlard) also are employed as a cookingmedium. In exceptional cases, sun-flower seed oil and/or partly hydro-genated sunflower seed oil is used as afrying medium. Generally, palm oil orslightly hydrogenated palm oil is usedfor producing pre-fried french fries.frozen chips, and other conveniencefoods. Increasingly, palm olein, becauseof its good performance due to naturalhigh oxidative stability, is becoming rhe

Table ICharacteristics of selected frying oils and fats

PalmPalm Palm "super"

RSO" HRSOb oil olein olein TallowFatty acid [wt %)C14:0 1.1 1.1 1.4 3.2C16:0 4.5 4.5 44.0 3'.8 33.7 24.3C18:0 1.5 5.5 4.5 4.4 3.6 18.6C18:1 5'.0 72.0 39.2 42.5 47.0 42.6C18,2 21.0 14.0 10.1 Il.2 13.8 2.6C18,3 J 1.0 1.0 0.4 0.6 0.4 0.7Others 3.0 3.0 0.7 0.4 0.1 8.oJIodine value 116 .0 53 58 65 47Slip point (0e) 13 38 22 4 43-45IPC (hours)

at 120°C 3-4 8-' 15-16 12-14 12-14 2-6

a Refined and deodorized rapeseed oil; bpanly hydrogenated rapeseed oil, which contained 22% trans fatty acids;c induction period, which indicates oxidative stability of the oil; dC16: 1,3.7%; C17:0, 1.5; C17: 1,0.8%.

oil of choice for the major snack foodmanufacturers in many EuropeanUnion counrries.

The more unsarurnred oil productsor special long-life oils containingblends of hydrogenated oils usuallyare used by caterers and the Fast-foodservice industry. lmpormur chnracrcr-isrics of industrial frying oils are highoxidative stability, high smoke point,low foaming, low melting point, blandflavor, and nutritionally desirableattributes. Table I gives characteristicsof some selected frying oils and fatsthat are used by the catering industry,fast-food sector, and snack rnnnufac-rurers.

Generally, in North America, the fry-ing industry and fast-food restaurantsemploy frying fats and shorteningsbased on cottonseed oil, hydrogenatedsoybean oil, and/or rapeseed oil. Severalnew frying oils having good stability areemerging on the horizon (Table 2), such

as Nu-Sun, a mid-oleic sunflower oil,and high-oleic sunflower seed oil.

Criteria of healthful frying oilThe concept of a healthful frying oil hasbeen questioned and debated to a con-siderable length. Since the lipid compo-sition of the fried food is thought to bean important factor at the time of fry-ing, appropriate criteria for the fattyacid composition of such an oil are con-sidered to be:

• rich in monounsaturated, C18:1(>75%),

• low in saturated (CI6:0, C14:0,C12:0) and polyunsaturated fatty acids(<15%),

• very low in linolenic acid, C18:3«1.5%), and

• practically zero content of transfatty acids

Moreover, it is commonly acceptedamong nutritionists that when therequirement of essential fatty acids

'"

(EFAs), n-3 and n-e fatty acids, is met inthe body, dietary lipids rich in monoun-saturated fatty acids, such as CIS: I, arebeneficial to the oxidative stability ofthe low-density lipoprotein (LOL) com-ponent of serum lipids. Several animalstudies have shown the superiority of anoleic-rich oil, such as high-oleic sun-flower seed oil (HOSO), over normalsunflower seed oil in generating LOL·cholesterol that is less prone to oxida-tion. These days, it is generally acceptedthat oxidized LOL-cholesterol initiatesthe early stage of atherosclerosis. Thehigher oxidative stability of LOL-cho-lcsrerol has been reported in humansubjects ingesting HOSO comparedwith those consuming normal sun-flower seed oil diets. Table 3 gives gen-eral guidelines about the effects of fattyacids on total cholesterol level andlipoproteins.

Healthful oils also should be rich innatural antioxidants, in tocopherols,

Volume I I • June 201Xl • Inform

Food Technology

Fatty acid Cholesterol level LOLa

Saturated Increase IncreaseTrans Increase IncreasePolyunsaturated Decrease Decrease

slightlyMonounsaturated Decrease Decrease

IncreaseDecreaseDecrease

Table 2Typical fatty acid composition of new frying oils and of normal sunflower seedoil and olive oil

Sunflower seed oils Olive oilParameter Nonnal No-Sun" HOSOb (virgin)Fatty acidCI6:D 7.0 8.8 4.3 9.2C18,0 4.5 2.3 4.2 3.3CIS: 1 IS.7 64.5 81.3 73.9CIS:2 67.0 22.1 8.2 10.0C18:3 0.8 0.4 <0.1 0.8Others 2.0 1.9 2.0 2.8

Iodine value 134 95 83 83IJ>C (hours)at 110°C 4.5 12 19 10

a Nu-Sun is mid-oleic acid sunflower seed oil, now grown commercially in theUnited States; b high-oleic sunflower seed oil; c induction period, which indicatesoxidative stability of the oil.

and preferably m j-rocopherol.Additional requirements of healthfuloils are rhar the fried product should bevery [ow in trails polyenes, in cyclicfatty acids, and in phytosterol oxides.Since the toxicity of cyclic furry acids

formed from linolenic acid, C 18:3,seems greater than that from linoleicacid, CI8:2, it appears beneficial tohave as little as possible linolenic acid ina frying oil. It should be mentioned herethat French regulations do not permit a

Table 3Effect of fatty acids on cholesterol and lipoproteins

No effect

a Low-density lipoprotein cholesterol ("bad" cholesterol); b high-density lipopro-tein cholesterol ("good" cholesterol).

Source: Yodice, R., Fat Sci. Tee/mol. 92:121-126 (l990).

Volume I I • June 2000 • Inform

,

HO6.s. Avenasterol

Citrostadienol

to)

A7- Avenasterol

Figure I:Structurel of sterols contilining ethylldene group

frying far or oil containing more [han1% linolenic ferry add to be used fordeep-fat frying in the catering industry.The formation of cyclic fatty acids has,however, been noticed to be negligibleduring continuous industrial frying.

Development of stable and healthfulfrying oilsThe concept of a stable frying oil cameinto existence when Alf Silkebergartended a course on frying at theUniversity of California-Davis, on May17, 1990. He left with one thought inmind: To produce a stable frying oil thatwould be low in saturates and wouldnot require hydrogenoricn. With the aidof scientists from Germany. India,Sudan, Sweden, and the United States, astable and healthful frying oil was ere-ared and is being marketed under thebrand name Good-Fry Oil. The maincomponent of this oil is high-oleic sun-flower seed oil. Its oxidative and flavorstability are funher enhanced by theaddition of a small portion of refinedsesame seed oil (550) and rice bran oil

(RBO). Table 4 provides typical charac-teristics of Good-Fry Oil and Good-FrySunclive Oil. The latter contains a smallportion of virgin olive oil. Both RBOand sesame oil contain large amounts of.o.5-ave.nasterol and related erhylidenegroup-containing sterols, which are in

a

'15

the region of 295~J55 mg/IOO g inRBO and 84-265 mg/100 g in 550,respectively.

Unlike most other sterols, .6.5-ave-nasrerol (and related sterols, namely,.6.7 -avenasterol and cirroscadienot](Figure 1) acts as an antioxidant at ele-vated/frying temperatures. This antioxi-dant activity has been ascribed to theformarion of an allylic free radical atC29 followed by isomerization to a rel-atively stable tertiary free radical at C24(Figure 2A). It should be emphasizedthat these ethylidene group-containingsterols show little or no antioxidantactivity at room temperature, 100°C, or120°C. That is, if one attempts to mea-sure oxidative stability of the oil con-mining such sterols by traditional meth-ods, for example, Rancimar or 051, theresults of their anrioxidative efficacywill be practically zero/negligible. Thisis probably due to formation of a less-hindered peroxy radical, which is inef-fective at interrupting free-radical chainreactions (Figure 2b). The formation ofthis peroxy radical from a stable hin-

N = Sterol ring

b

H

Figure l:Hechanisms for andoxldant ..ctivity of sterols containing ethylidene group in theside ch;ain, (h) fonn ..tlon of stable tertiary free r.adial <It C14 and (lb) fonn ..tion of len-stable p4!roX)' r.adlcal

Volume II • lune 2000 • Inform

Food Technology

Table'"Typical characteristics of Good-Fry frying oils

Q Contains a small portion of refined sesame oil and rice bran oil, produced according ro patent (Silkeberg and Kochhar;1998); b in addition to (Q), also contains 10% virgin olive oil;' including cryzancl, sesame lignans, 65_ and a7-avenasterol,and desmeehylsrerols.

ParameterAppearanceFlavorIodine valuePeroxide valueFree fatty acids

Fatty acid (% weight)C16,0C18,0C18:1C18:2C18,3OthersTrans Farry acidsVitamin EOther anrioxidarivecomponents'

dered radical derived from a5-avenas-rerol is favored at high partial pressuresof oxygen. During frying of food, anoxygen deficiency caused by steamvolatilization in the frying oil favors rheformation of a stable tertiary radical atC24 (Figure 2A). Another beneficialeffect of ethylidenc group-containingsterols is that they retard the loss oftocopherols in heated oils and thusenhance the frying life of the oil andsubsequently prolong shelf-life of friedsnacks.

A range of other potent componentssuch as sesamolin (antioxidant precur-sor), sesaminol and its isomers, sesamoland its dimer present in sesame seed oil,and oryzanol (a group of ferulic acidesters of sterols) present in RBO havebeen shown to possess strong srabiliz-inglbeneficial effects during frying cper-

Volume I I • June 2000 • Inform

Good-Fry oil°Clear, transparentBland, no foreign odor84-90, typical 861.0 meq 02/kg0.05% as oleic acid

4.53.7

78.610.70.12.4

<0.540 mgfloo g

100 mg/loo g

anons. Figure 3 presents the mecha-nisms for the liberation of sesamol andsesaminol isomers from sesamolin dur-ing the frying operation. The protectiverole of sterol ferulares (oryzanol) can beexplained by the formation of five reso-nance-stabilized Structures (Figure 4)that are very effective at interrupting theauroxidnrion chain reactions.Moreover, sesame oil contains 40--60mgltoO g of tocopherols, mainly 't-tocopherol, while RBO contains70-140 mg/IOO g tocopherols, 50-80%of which are j-roccpberol and )'-roconienol.

It is interesting to note thatsesamol and sesarninol compoundsshow synergistic effects with j-rocc-pherol and retard the degradation ofa-tocopherol at frying temperature.These potent antioxidative compo-

Good-Fry sunolive oj]bClear, transparentMild olive oilTypical 861.5 meq 02/kg0.15% as oleic acid

5.03.6

78.310.70.22.2

<0.538 mg/IOO g

100 mg/IOO g

nents and precursors are largelyretained by means of the special refin-ing procedure, patented for the pro-duction of the Good-Fry Constituents(GFC), which are a blend of refinedsesame seed oil and RBO.

To sum up, this stable edible oilwas initially creared for two purposes:(a) to be as healthful as virgin oliveoil, and (b) when used for industrialfrying, to be as stable or more stablethan partially hydrogenated liquid oilsandlor palm oil. However, this stableoil can be used for other food applica-tions. This oil has been approved forlabeling as a "dietetic" oil by theFederal Institute for the HealthProtection of the Consumers in Berlin,Germany. The edible oil is now com-mercially available in Europe. Thesun-olive oil, with a mild olive oil fla-

vor, is sold in retail stores in Swedenand also is available to retailers inorher countries. Also, this type of sta-ble frying oil, with irs Mediterraneanimage of healthful diet is being adopt-ed by several European Union snackmanufacturers for producing healthfulsnacks of excellent taste and quality.Moreover, for consumers concernedwith low-fat diers, these oils can alsobe used to manufacture many conve-nient foods for healthful eating in thenew cenrury.

BibliographyNew Developments of industrial

Prying, edited by S.P. Kochhar, PJBarnes & Associates, Bridgwater,United Kingdom, 1997.

Blumenthal, M.M., A New Look at theChemistry and Physics of Deep-FatFrying, Food Technol. 45:68-71(1991).

Kochhar, S.P., Safety and Reliabilityduring Frying Operations-Effects ofDetrimental Components and FryerDesign Features, in Fryi"g of Food,edited by D. Bcskcu and I. Elmadfa,Technomic Publishing Co. lnc.,Lancaster, Pennsylvania, 1999, pp253-269.

Silkeberg, A., and S.P. Kochhar,Refining of Edible Oil RetainingMaximum Antioxidative Potency,European Patent Application No.98102528.1-2109, 13.02.98 andother worldwide patent applicationspending, 1998.

Willer. W.c., and A. Ascheno, TrailSFatty Acids: Are rhe Effects OnlyMarginal? Am. l- Public Health84:722-724 (1994).0

(A)

+ o~ ~ _.

Sesamol ~""SesamolinSamin

(8)

~ ~::.~j"

Sesamol;~'C0 I ~

,. -~'~', .~ .~2~ . . I .~~aminOI ~6 E . . I-apr-sesammc ~ /¥, - pi-sesammo

.~Diasesamlnol

Figure l:Hechanisms fol"the liberation of segmol (A) and sesaminol isomer'S(8) from~samolin during frying operation

coost COOSt

ccse

oFigu", -4: Resonanc. stabill:r.edstructures of sterol ferulate

Volume II • June 2000 • Inform