OXIDATIVE AND FLAVOR STABILITY OF TORTILLA CHIPS FRIED IN EXPELLER PRESSED LOW LINOLENIC ACID SOYBEAN OIL

OXIDATIVE AND FLAVOR STABILITY OF TORTILLA CHIPSFRIED IN EXPELLER PRESSED LOW LINOLENIC ACID

SOYBEAN OIL*

KATHLEEN WARNER1

National Center for Agricultural Utilization ResearchAgricultural Research Service

1815 North University St.U.S. Department of Agriculture

Peoria, IL 61604

Submitted for Publication January 5, 2009Revised Received and Accepted January 26, 2009

ABSTRACT

To determine effects of expeller oil pressing and decreased linolenic acid,intermittent batch frying tests were conducted with tortilla chips usingsoybean oil (SBO), expeller pressed SBO (EPSBO), expeller pressed lowlinolenic SBO (EPLLSBO), high oleic sunflower oil, corn oil and hydroge-nated SBO for up to 35 h of frying. Chips were aged at 25C and trained,experienced analytical sensory panelists evaluated their flavor. Oxidative sta-bility of the chips was determined by hexanal analyses and oil fry life wasmeasured by total polar compounds. The stability of tortilla chips fried inEPLLSBO was significantly better than chips fried in SBO or EPSBO asjudged by rancid flavor intensity and hexanal formation after storage. Thiseffect may be due, in part, to less linolenic acid in EPLLSBO and bettertocopherol retention compared to EPSBO. The combination of expeller press-ing and low linolenic acid (EPLLSBO) produced a significantly more stablefried product than expeller pressing (EPSBO) alone.jfl_1137 133..147

PRACTICAL APPLICATIONS

Food manufacturers are interested in oils that can be used for frying asalternatives to trans fat-containing hydrogenated fats. Since polyunsaturated

* Disclaimer: Names are necessary to report factually on available data; however, the USDA neitherguarantees nor warrants the standard of the product, and the use of the name by USDA implies noapproval of the product to the exclusion of others that may also be suitable.

1 Corresponding author. TEL: (309) 685-4011; FAX: (309) 681-6668; EMAIL: [email protected]

Journal of Food Lipids 16 (2009) 133–147. All Rights Reserved.© 2009, Wiley Periodicals, Inc. 133

vegetable oils are not sufficiently oxidatively stable for frying, alternativessuch as modified fatty acid composition oils, additives and oil processingtechniques could be used individually or in combination to increase fry life ofthe oil and shelf life of foods. Although expeller pressing of SBO or reducinglinolenic acid of SBO alone have not given SBO the stability equivalent toHSBO, we found that combining decreased linolenic acid and expeller press-ing of SBO produced frying oil and fried tortilla chips with the stability similarto that of hydrogenated fat in early stages of frying.

INTRODUCTION

Polyunsaturated vegetable oils are usually oxidatively stable for saladoils; however, in high stability applications such as frying, these types of oilsare not resistant to the deteriorative processes of oxidation, hydrolysis andpolymerization that occur during frying. To solve this problem in the past, oilswere hydrogenated and contained additives to increase the fry life of the oiland the shelf life of foods. Now, food manufacturers are investigating alterna-tives to hydrogenated oils because of the interest in decreasing or eliminatingtrans fatty acids. Potential solutions include modification of fatty acids in theoil such as increasing oleic acid and decreasing linoleic and linolenic acids.Evans et al. (1965) reported that linolenic acid should be decreased to less than5% to improve oxidative stability of soybean oil (SBO) when it was evaluatedas an aged salad oil. However, the level of linolenic acid was recommended tobe lower for frying oils because linolenic acid-containing vegetable oils suchas canola and soybean produced off-flavors and odors such as fishy and acridwhen they were exposed to high temperature heating (Evans et al. 1965; Eskinet al. 1989). In literature reports on modified fatty acid composition oils,linolenic acid content in canola and soybean oils was usually decreased to lessthan 3% (Miller and White 1988; Warner and Mounts 1993; Mounts et al.1998) and oleic content of safflower, canola and sunflower was increasedabove 80% with a corresponding decrease in linoleic acid (Fuller et al. 1967;Niemala et al. 1996; Petukhov et al. 1999). These authors reported thatincreasing oleic acid and decreasing linoleic and linolenic acids increased oilstability. However, they also found that most oils with modified fatty acidsincluding low linolenic acid oils did not perform as well as hydrogenated oilfor frying because they did not have enough oxidative stability. In addition tomodifying fatty acids, alternative oil extraction such as expeller pressing hasbeen shown to improve oil stability (Hill 1992; Wang and Johnson 2001;Warner and Dunlap 2006). Warner and Dunlap (2006) reported that expellerpressed oils produced Maillard reaction products that possibly acted as naturalantioxidants; however, they found that expeller pressed SBO (EPSBO) did not

134 K. WARNER

have as good a fry life as hydrogenated SBO (HSBO). Even though modifiedfatty acid composition and expeller pressing individually might not create oilstability equivalent to HSBO, combining expeller pressing with modified fattyacid composition such as low linolenic acid might produce oils that havestability similar to that from hydrogenation. The objective of this research wasto determine if EPSBO and expeller pressed low linolenic SBO (EPLLSBO)were oxidatively stable for frying foods in batch operations in comparison withunmodified SBO and common frying oils such as high oleic sunflower oil(HOSUN), corn oil and HSBO.

MATERIALS AND METHODS

Materials

Hexane extracted, alkali refined, bleached and deodorized oils includingSBO, HOSUN, corn oil and HSBO were obtained from commercial proces-sors. EPSBO (Nexsoy, Springfield, IL) and EPLLSBO (Innovative Growers,Mason City, IA) that were physically refined, bleached and deodorized werealso commercially processed. All oils contained citric acid as the only additive.Tocopherol standards (a-, b, g-, d-tocopherols, at 95% purity, were purchasedfrom Matreya, Inc. (Pleasant Gap, PA). All other chemicals and solvents wereobtained from Sigma-Aldrich (St. Louis, MO), unless otherwise stated, andwere American Chemical Society grade or better. White corn tortillas wereobtained at a local grocery store.

Intermittent Batch Frying of Tortilla Chips

Each tortilla (15 cm diameter) was cut into six equal wedges and 50 gbatches were fried for 90 s at 180 � 2C in a 2-L capacity fryer (NationalPresto Industries, Eau Claire, WI) containing 1,200 g oil initially. Tortilla chipswere fried every 15 min for 7 h each day for 5 days. Oil and chip samples werecollected at 5, 15, 25 and 35 h of frying. Fresh make-up oil (60 g) was addedevery 5 h of frying after the oil and chip samples were collected. Tortilla chipswere placed in 1-L wide-mouth glass jars with air in the headspace and eachjar was closed with a screw cap. Chips were aged in the jars in the dark for 0,1, 2 and 4 months at 25C then frozen at 0C for later analyses.

Compositional Analyses of Oils

Fatty acid compositions of the initial oils were determined in duplicateby capillary gas chromatographic analysis with a Hewlett-Packard 5,890 gaschromatograph (GC) (Wilmington, DE) equipped with an SP2330 column

135FRYING STABILITY OF EXPELLER PRESSED SOY OILS

(30 m, 0.20 mm ID, 0.20 micron film thickness) (Supelco, Bellefonte, PA).Column temperature was first held at 190C for 5 min, and then was pro-grammed to 230C at 20C/min. The injector was held at 250C and the detectorat 260C.

Analysis a-, b, g-, d-tocopherols by normal-phase HPLC was conductedin triplicate using a Varian ProStar (Varian Associates, Inc., Walnut Creek, CA)with a Model 363 fluorescence detector. The detector was set at 290 nm forexcitation and 330 nm for emission. The HPLC was fitted with a 5-mm VarianInertsil Si column (250 ¥ 4.6 i.d.). The isocratic solvent system, 0.5%2-propanol in hexane, was pumped at 0.5 mL/min. Quantification of thetocopherols was made using external standard calibration.

Analysis of Oil Quality and Stability

Initial quality of the fresh oils was measured in duplicate by peroxidevalue (PV) using AOCS (1998) method Cd 8-53. The oxidative stability index(OSI) of the fresh oils was measured at 110C using an Oxidative StabilityInstrument (Omnion Inc., Rockland, MA) according to AOCS (1998) methodCd 12b-92. Total polar compound (TPC) levels of the fresh and used fryingoils were determined in duplicate by the AOCS (1998) column chromatogra-phy method Cd 20-91.

Flavor and Oxidative Stability Analyses of Tortilla Chips

Hexanal levels in the fresh and aged tortilla chips were analyzed induplicate with a purge and trap apparatus equipped with a test tube adapter(Tekmar model 3000, Tekmar-Dohrmann Co., Cincinnati, OH) coupled with aVarian model 3400 GC and a Saturn model 3 ion trap mass spectrometer (MS)(Varian, Inc., Walnut Creek, CA). A 50-mg ground chip sample was placed ina 1.9 ¥ 7.6 cm test tube and heated at 100C for 9 min preheat time. Volatilecompounds were trapped on a 30.5 cm Tenax #1 trap, with 10 min samplepurge time, 170C for 6 min desorbing, 180C desorb temperature, 160C GCtransfer line and valve temperature. Volatile compounds were introduced ontoa DB-1701 GC capillary column (30 m ¥ 0.32 mm with 1 micron film thick-ness) (J & W Scientific, Folsom, CA). The column was held at -20C for 2 min,and then heated from -20C to 233C at 3C/min. Column helium flow rate was2 mL/min with 28 mL/min injector split vent flow. GC injector was set at 240Cand the line to the mass spectrometer was set at 230C. The ion trap MSoperated in electron ionization mode with mass scan range 23–400 m/z over0.8 s. Filament emission current was 25 micro amps, axial modulation was2.1 v, manifold heater was set at 160C and filament/multiplier delay was2.5 min. Compound structural identifications were made both from spectralcomparisons with the NIST 92 mass spectrometry library (Varian, Inc.) andfrom retention time comparisons with standard compounds.

136 K. WARNER

A 15-member analytical descriptive sensory panel, trained and experi-enced in evaluating fried foods rated the chips for intensities of individualflavors including deep fried, stale, rancid and hydrogenated on a 10-pointintensity scale with 0 = no intensity and 10 = strong flavor intensity (Warnerand Gupta 2005). Each panelist was presented with 5 g crushed chip samplesat room temperature in 59.2 mL plastic cups with snap-on lids (Solo CupCompany, Urbana, IL). Each panelist received four coded, randomizedsamples of each fry time (e.g., 5 h) at each storage time (e.g., 1 month) persession. All sensory evaluations were conducted at our research center in apanel room with individual booths, temperature control and with red lightingto mask color differences between samples (Warner 1995).

Statistical Analysis

Data were evaluated by analysis of variance and Duncan’s multiple rangetest (Snedecor 1956). Statistical significance is expressed at the P � 0.05 levelunless otherwise indicated.

RESULTS AND DISCUSSION

Fatty Acid Composition

The fatty acid compositions of the oils used for intermittent batch frying(Table 1) showed the total amount of saturated fatty acids ranging from 14.2 to16.7% in all oils except for the HOSUN, which had a low level of 6.5%. Oleicacid levels ranged widely with a low of 21% for EPSBO to a high of 83.2% for

TABLE 1.FATTY ACID COMPOSITIONS OF OILS

Fatty acids Corn HOSUN HSBO EPSBO EPLLSBO SBO

C14:0 0.1 0.0 0.0 0.0 0.1 0.1C16:0 10.6 3.4 10.7 10.8 9.1 10.4C18:0 2.0 3.1 6.0 5.0 4.9 4.7C18:1 trans 0.0 0.0 20.0 0.0 0.0 0.0C18:1 cis 27.4 83.2 44.0 21.0 28.2 24.1C18:2 trans 0.0 0.0 2.2 0.0 0.0 0.1C18:2 cis 58.2 8.8 16.2 53.5 55.4 52.7C20:0 0.5 0.3 0.0 0.4 0.4 0.5C18:3 1.2 0.1 0.6 8.9 1.5 6.9C22:0 0.2 1.0 0.2 0.4 0.5 0.5

HOSUN, high oleic sunflower oil; HSBO, hydrogenated soybean oil; EPSBO, expeller pressed SBO;EPLLSBO, expeller pressed low linolenic SBO; SBO, soybean oil.


HOSUN. Linoleic acid values were similar for corn oil, SBO, EPSBO andEPLLSBO, ranging from 52.7 to 58.2%; however, the levels were low forHOSUN with 8.8%, and HSBO with 16.2%. EPSBO had the highest amountof linolenic acid (8.9%) followed by SBO with 6.9%. All other oils had a rangeof linolenic acid of 0.1–1.5%. The HOSUN and HSBO would be expected tohave the best frying stability and fried food stability because of their low levelsof linoleic and linolenic acids alone. In contrast, SBO and EPSBO would beexpected to have the lowest stability based on fatty acid composition alone.

Initial Oil Quality

The oils were evaluated to measure initial oil quality (Table 2). The initialPV levels for all oils were low with a range of 0.1–0.6. OSI measurementswere significantly different for all oils except for corn and EPLLSBO. The OSIlevel was highest for HSBO, followed by HOSUN, corn and EPLLSBO.Lowest OSI hours were measured in the SBO and EPSBO. The tocopherolprofiles were typical for each oil type and showed significant differencesbetween oil types indicating that these differences could be expected to affectfrying oil stability and fried food stability (Wagner and Elmadfa 2000).

Oil Deterioration

Total polar components were measured as an indicator of the level ofdeterioration in the frying oils. Houhoula et al. (2003) found that the amountsof polar compounds increased linearly with increasing frying time. Theamounts of TPC formed in the oils in this study at sampling times of 0, 5, 15and 35 h are presented in Table 3. SBO and EPSBO had significantly higher

TABLE 2.INITIAL VALUES FOR OILS

Analyses† Corn HOSUN HSBO EPSBO EPLLSBO SBO

Peroxide value (meq/kg) 0.6a 0.4a 0.4a 0.5a 0.4a 0.1bOSI (110C) h 9.2c 16.7b 22.7a 3.5e 8.9c 5.4dTocopherols (ppm)

a 278b 1165a 114d 84e 75f 166cb 9d 42a 27b 22c 22c 27bg 918a 12e 798b 722c 625d 796bd 37e 1f 257b 288a 220c 189d

† Values between oil types for each analysis are significantly different if no letter in common in eachrow (P � 0.05); see Table 1 for oil identification.

OSI, oxidative stability index; HOSUN, high oleic sunflower oil; HSBO, hydrogenated soybean oil;EPSBO, expeller pressed SBO; EPLLSBO, expeller pressed low linolenic SBO; SBO, soybean oil.

138 K. WARNER

TPC than the other four oils at 5, 15 and 35 h sampling times; however, onlySBO had a TPC close to the discard level of 25% TPC (DGF 2000) after 35 hof frying. The TPC levels in corn oil, HOSUN, HSBO and EPLLSBO were allless than 11%, even after 35 h of frying. The results for TPC generally corre-lated with the fatty acid compositions of the oils. For example, the SBO andEPSBO with high levels of linolenic acid had the highest percent of TPC.On the other hand, HSBO with the highest level of saturates and a low amountof polyunsaturates had the lowest percent of TPC.

Oxidative Stability of Tortilla Chips

Hexanal was used to monitor the oxidation of the aged tortilla chips afterambient temperature storage because it is a major volatile compound formedduring fatty acid oxidation (Frankel 2005). Hexanal analysis was conducted ontortilla chips aged at 1, 2 and 4 months at 25C after 5 and 35 h of intermittentfrying. In the unaged tortilla chips fried in oils used for 5 h, hexanal levelswere similar between oils and ranged from 1 to 4 ppm; however, after 1 monthstorage, slight differences began to appear (Fig. 1). For example, chips fried incorn oil, HSBO, EPLLSBO and HOSUN had the lowest levels of hexanal andthe chips fried in EPSBO and SBO had slightly higher amounts. At the 2months storage time, chips fried in corn oil, HOSUN, HSBO and EPLLSBOall had less than 5 ppm hexanal; but hexanal induction periods were observedfor chips fried in EPSBO and SBO with levels of 10 ppm and 25 ppm, respec-tively, that were significantly higher than the chips prepared in the other fouroils. At the 4 months storage time, the chips fried in SBO had 70 ppm hexanal

TABLE 3.TOTAL POLAR COMPOUNDS† (%) IN FRYING OILS USED

FOR UP TO 35 h

Intermittent batch frying (h)

0 5 15 35

Corn 2.6a 5.1c 7.1c 10.8cHOSUN 1.7b 4.5d 5.8e 9.6dHSBO 1.7b 3.5e 4.9f 8.4eEPSBO 1.8b 5.5b 11.1b 20.7bEPLLSBO 1.8b 4.3d 6.4d 10.3cSBO 1.7b 7.1a 14.1a 23.3a

† Values between oil types at each time interval are significantlydifferent if no letter in common in each column (P � 0.05).

HOSUN, high oleic sunflower oil; HSBO, hydrogenated soybean oil;EPSBO, expeller pressed SBO; EPLLSBO, expeller pressed lowlinolenic SBO; SBO, soybean oil.


0 1 2 3 40

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FIG. 1. HEXANAL IN TORTILLA CHIPS FRIED IN OILS (SBO, CORN, HOSUN, HSBO,EPSBP AND EPLLSBO) USED FOR 5 OR 35 h OF INTERMITTENT BATCH FRYING AT

180C; CHIPS STORED AT 25CSBO, soybean oil; HOSUN, high oleic sunflower oil; HSBO, hydrogenated SBO; EPSBO, expeller

press SBO; EPLLSBO, expeller press low linolenic SBO.

140 K. WARNER

that was not plotted in Fig. 1 because of the high value. Tortilla chips fried inHOSUN, HSBO and EPLLSBO used for 5 h were the most stable after 4months of aging; however, chips fried in corn oil and EPSBO had significantlyhigher hexanal levels. In chips fried in oils used for 35 h (Fig. 1), a similarpattern of hexanal formation was observed as in the chips fried in oils used for5 h. For example, the SBO sample had significantly more hexanal formed after1 month storage than chips fried in the other oils. By 2 months of storage,hexanal was lowest in the chips fried in HOSUN, corn oil and HSBO, followedby EPLLSBO. The chips fried in EPSBO had a significantly higher amount ofhexanal with 27 ppm and the SBO chips had an extreme hexanal level of110 ppm (data not plotted). After 4 months of aging, chips fried in HOSUNhad a significantly lower hexanal level than the other oils, followed by HSBO.No significant difference in hexanal levels was observed between corn oil andEPLLSBO. Also, the chips fried in EPSBO at 35 h had 72 ppm hexanal thatwas not plotted in Fig. 1 because of the high value. Expeller pressing of theSBO (EPSBO) significantly improved the oxidative stability of chips com-pared to those fried in SBO; however, the combination of low linolenic acidand expeller pressing produced an oil (EPLLSBO) that gave chips similarstorage stability to HSBO or HOSUN after 5 h of frying and stability equiva-lent to chips fried in corn oil after 35 h of oil use.

Flavor Stability of Tortilla Chips

Flavor analyses were conducted on tortilla chips sampled after the oilswere aged for 0, 1, 2 and 4 months after 5 and 35 h of intermittent frying. Deepfried flavor intensity was monitored as the primary positive flavor attribute.Intensities of negative flavor attributes, stale, hydrogenated and rancid werealso measured. In most fried foods such as potato chips and tortilla chips, adeep fried flavor is the predominant attribute in an unaged sample; however,the intensity of this flavor is dependent on the fatty acid composition of the oilsused to fry the food (Warner et al. 1994, 1997, 2001). For example, oils withhigh levels of linoleic acid produce large amounts of 2, 4-decadienal, which isconsidered a primary source of deep fried flavor (Frankel 2005). On the otherhand, oils such as HOSUN with low levels of linoleic acid (8–9%) produceonly low levels of 2,4-decadienal and, therefore, low intensity levels of deepfried flavor (Warner et al. 1994). In the samples fried in oils used for 5 h, theunaged tortilla chips fried in the EPLLSBO had the highest intensity of deepfried flavor, followed by chips fried in corn oil, EPSBO and SBO (Fig. 2a).This would be expected because these oils had linoleic acid levels rangingfrom 52.7–58.2%.

Unaged chips fried in HSBO and HOSUN had the lowest deep-friedflavor intensities primarily because their lower linoleic acid content ranged


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1 2 3 4 0 1 2 3 4

0 1 2 3 40 1 2 3 4

0 1 2 3 4 0 1 2 3 4







FIG. 2. FLAVOR INTENSITIES FOR TORTILLA CHIPS FRIED IN OILS (SBO, CORN,HOSUN, HSBO, EPSBO AND EPLLSBO) USED FOR 5 or 35 h OF INTERMITTENT BATCH

FRYING AT 180C; CHIPS STORED AT 25C(A) Deep fried at 5 h, (B) deep fried at 35 h, (C) stale at 5 h, (D) stale at 35 h, (E) Rancid at 5 h.(F) Rancid at 35 h. SBO, soybean oil; HOSUN, high oleic sunflower oil; HSBO, hydrogenated

SBO; EPSBO, expeller press SBO; EPLLSBO, expeller press low linolenic SBO.

142 K. WARNER

from 8.8–16.2%. As the amount of storage time increased, the intensity of deepfried flavor decreased probably because negative flavors developed. A similarpattern of results was seen for the chips fried in oils used for 35 h (Fig. 2b).Flavor intensity values for samples with the very high hexanal levels are notplotted in figures showing flavor data since these samples were not evaluatedfor flavor because of strong rancid flavor intensity. The intensity of deep friedflavor in most of the samples fried in oils used for 35 h decreased duringstorage because of the intensity of negative flavors increased, probablymasking some of this positive flavor. However, the chips fried in HOSUN andHSBO had low intensities of deep fried flavor initially and the intensities ofthis flavor remained fairly constant during storage. The chips fried in HSBOhad a weak to moderate intensity of hydrogenation flavor (data not shown).

Stale flavor intensity generally increased with increasing storage time forchips fried in oils used for 5 h (Fig. 2C). In chips fried in oils used for 35 h(Fig. 2D), the stale flavor intensities increased during early stages of storage,but began to decrease between 2 and 4 months, probably because of increasesin rancid flavor intensity. In the samples fried in oils used for 5 h, the tortillachips fried in the SBO had the highest intensity of rancid flavor after 1 monthof aging (Fig. 2E). The rancid intensities of the tortilla chips fried in the otherfive oils were at intensities of 1.0 or less indicating a very weak rancid flavor.By 2 months of storage, the chips prepared in SBO had significantly higherrancid flavor intensity than the other samples followed by the chips fried inEPSBO. All other chips samples had rancid intensities less than 0.6. After 4months of aging, the chips fried in HSBO, HOSUN and EPLLSBO all hadrancid flavor intensities less than 0.5, but the corn oil chips had a significantlyhigher intensity followed by chips fried in EPSBO. The SBO samples were nottasted because of the strong rancid flavor intensity. Similar patterns wereobserved at 35 h of frying (Fig. 2F) as for 5 h (Fig. 2E); however, by 2 and 4months, chips prepared in HOSUN and HSBO had significantly lower rancidflavor than chips fried in the other oils. The tortilla chips fried in the SBO andEPSBO had significantly higher intensities of rancid flavor than tortilla chipsfried in the other oils (data not plotted). The intensities of rancid flavorincreased with increasing hexanal levels (Fig. 1).

Retention of Tocopherols in Frying Oils

Measuring disappearance of tocopherols in oils has been used to deter-mine the effect of antioxidants and oil stability during frying (Gordon andKourimska 1995; Wagner and Elmadfa 2000). In our study, after 5 h of frying,SBO and EPSBO had lost the most tocopherols of any of the oils and thispattern also continued at both 15 and 35 h with only a few exceptions(Table 4). These results paralleled the decrease in fry lives of these two oils


(Table 3) and the decrease in their shelf lives as measured by hexanal forma-tion (Fig. 1). Corn oil and EPLLSBO retained the most tocopherols, with theexception of the d–tocopherol loss in EPLLSBO (Table 4). The retention oftocopherols and fatty acid compositions of corn oil and EPLLSBO could helpexplain the stability of the aged chips fried in these oils. Although it might beexpected, HOSUN and HSBO did not have the lowest level of tocopherol loss.This situation may be because less polyunsaturated oils lose more tocopherols

TABLE 4.RETENTION (%) OF TOCOPHEROLS IN OILS USED FOR UP

TO 35 h OF FRYING

Intermittent batch frying (h)

5 15 35

Corna 96 95 94b 99 99 99g 97 83 70d 100 92 90

HOSUNa 93 72 61b 95 79 64g 92 75 58d 95 94 93

HSBOa 93 90 75b 87 83 65g 84 63 27d 94 90 69

EPSBOa 51 50 44b 86 80 75g 55 44 31d 84 76 68

EPLLSBOa 99 98 96b 94 93 92g 93 87 72d 86 75 68

SBOa 47 25 22b 45 33 26g 37 13 11d 70 48 1

HOSUN, high oleic sunflower oil; HSBO, hydrogenated soybean oil;EPSBO, expeller pressed SBO; EPLLSBO, expeller pressed lowlinolenic SBO; SBO, soybean oil.

144 K. WARNER

because the hydroperoxides are stable and remain in the oil to react withtocopherols and degrade them (Frankel 2005).

CONCLUSIONS

Expeller pressing of the SBO significantly improved the fry life of the oiland storage stability of the tortilla chips compared to chips fried in conven-tional hexane extracted SBO. However, combining low linolenic acid levels ina SBO with the use of expeller pressing improved oil stability significantlymore than expeller pressing alone and produced a frying oil with stabilitysimilar to HOSUN and HSBO at the 5 h frying time. Comparing the toco-pherol retention of the three SBO samples (SBO, EPSBO and EPLLSBO),showed significantly different patterns that corresponded to the stability of thetortilla chips fried in these oils. For example, the highest amount of tocopherolloss was in the SBO, which produced the chips with the lowest stability asmeasured by hexanal formation. EPLLSBO had low tocopherol losses andgood stability. A direct comparison of EPLLSBO and low linolenic acid SBOwas not included in this study and will be the subject of a future project.

ACKNOWLEDGMENTS

L. Parrott, W. Rinsch and K. Steidley provided technical assistance andthe sensory panel.

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OXIDATIVE AND FLAVOR STABILITY OF TORTILLA CHIPS FRIED IN EXPELLER PRESSED LOW LINOLENIC ACID SOYBEAN OIL