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INFLUENCE OF TEMPERATURE AND LIGHT EXPOSURE ONSUNFLOWER OILSENSORY SHELF-LIFE OF A COMMERCIAL

GUILLERMO R A M k E Z , GUILLERMO HOUGH and ADRIANA CONTARINIInstimto Superior Experimental de Tecnologfa Alimentaria

6500) Nueve de JulioBuenos Aires, ArgentinaAccepted for Publication May 1 , 2000

ABSTRACTThe objectives of the present work were to: I ) correlate consumeracceptability measured with a consumer panel versus oxidized flavor m easuredwith a trained sensory panel to thus define the sensory failu re of a commercialsunflower o il; and (2)study the effect of storage temperature and light exposureon the sensory shelf-life of sunflower oil bottled in polyethylene tetraphtalatePEQ with nitrogen in the headspace. Of the consumers, 15 unexpectedlypreferred the more oxidized oil samples than the resh ones. Their data were notconsidered in sensory ailure calculations. By correlating the consumer data withthe trained sensory panel data, a sensory failu re point of 3.6 on a 0 to 10oxidation lavor scale was obtained. Both storage temperature and exposure tolight had a significant ef ec t on she lf-life. Estimated shelf-lives at an ambienttemperature of 2 C were 281 days for light exposed oil, and greater than 2years fo r oil kept in the dark.

INTRODUCTIONSunflower oil (SO) is of great commercial interest to Argentina. World wide

the yearly per-capita consumption of vegetable oil is 12 kg of which 12corresponds to SO. In Argentina the yearly oil per-capita consumption is 16 kg,of which 75 corresponds to SO (Muiioz 1997). Argentina produces 20 of theworld sunflower crop, and exports 55 of its own SO production.

The effect of light on oxidation of lipids is well known (Nawar 1996). Wan(1995) describes a method to study the effect of light exposure on oils in a clearglass bottle with air in the headspace, and Kiritsakis (1998) studied the relativeeffect of plastic and glass bottles on the oxidation of olive oil exposed to light

Corresponding author Email: guille@ghough cyt edu ar Author Hough is a research fellow of th eC om is ih de Investigaciones Cientificas de la Provincia de Buenos Aires.Journal of Food Quality 24 2001) 195-204. A21 Rights Reserved.Copyright 2001 by Food & Nutrition Press Inc. Trumbull Connecticut. 195


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196 G . RAMiREZ. G . HOUGH and A. CONTARINI

and in bottles wrapped with aluminum foil; in both cases light exposure had asignificant effect on flavor deterioration. There is limited information on shelf-life of vegetable oils stored in their original bottles; Labuza 1982) omparedshortening with sunflower oil by an active oxygen method. The effect of lightexposure on the sensory shelf-life of SO packaged in polyethylene tetraphtalate(PET) with nitrogen in the headspace has not been reported.

Failure criteria in sensory testing is not uniform. Gacula 1975)useddifferent cutoff points according to the product/situation: on a (none) to 7(very strong) off-flavor scale he used 2.5 for one product and 3.5 for another.Randell f al. 1995) sed a quality scale from0 (unacceptable) to 5 (excellent),and considered products with scores I2 s unacceptable for sale and 1.5unfitfor human consumption. Oconner-Shaw f al 1994) used qualitatitbeappraisals such as lower typical odor. Other authors (Vaisey-Genser et al1994;Vankerschaver et al 1996) ave asked consumers if they would consumethe product utilizing yes-no answers. From this brief review it is clear that thereare no standards for defining sensory failure of food products.A consumer panel would be the most appropriate one to determine when afood product reaches the end of its shelf-life. To repeatedly assemble consumerpanels for the multiple measurements needed during shelf-life studies would beimpractical and expensive. A trained sensory panel is a lot simpler to assemble,but yields analytical answers such as degree of oxidized flavor. How high doesthe oxidized flavor need to be for the sensory acceptability of the product todecrease? The answer to this question can be obtained by correlating dataobtained from a consumer panel with data obtained from a trained panel.

The objectives of the present work were: (a) correlate consumer acceptabili-ty with oxidized flavor to define the sensory failure of SO, and (b) study theeffect of storage temperature and light exposure on the sensory shelf-life of acommercial SO.

MATERIALSAND METHODSo l

Samples were commercial SO provided by AGD Inc. (General Deheza,Cbrdoba, Argentina), packaged in 1 PET bottles with nitrogen in the headspace. The oil had been refined as follows: settling and degumming, neutraliza-tion, bleaching and deodorization (Nawar 1996).Sensory Evaluation by a Trained Panel

A panel of 12assessors were selected and trained following the guidelinesof the IS0 1993) tandard. They all had a minimum of 12months experiencein discrimination and descriptive tests.


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SENSOR Y SHELF-LIFE OF SUNFLOWER OIL 197

Oxidized flavor was measured following the guidelines of the AOCS (1989).10 cm3 of oil were placed in 70 cm3 glasses, and covered with a 6 cm diameterPetri dish. The covered glasses were heated to 50f 1C in a microwave oven,and then placed in a 27x 16x 14 cm expanded polystyrene covered box, partiallyfilled with water at 60C to help maintain the temperature during sensoryanalysis. Effective temperature at tasting was 5 0 f2 C . Red lighting was used toeliminate color cues. Assessors used water at approximately 40C to cleansebetween samples.

To familiarize the trained panel with oxidized notes, SOwas stored for 14days at 60C in a tinned pail exposed to air (AOCS 1989). On a 10 cmunstructured oxidized flavor scale, anchored with none to extrem e , theresulting sample was considered extreme. A 10% dilution in fresh SO wasplaced mid way on the scale. Once assessors had registered these references,they were monitored by analyzing the following samples of SO:(1) fresh,(2) stored bottled at 60C during 20 days, with and without illumination, and3) stored bottled at 60C during 35 days, w ith and without illumination;i.e. a total of 5 samples which were analyzed in triplicate at different sessions.Consumer Panel

The consumer panel had a total of 60 consumers, 30 men and 30 women,all users of SO, with no previous experience in sensory analysis. As a carrierto taste the oils they used 1 cm3 cubed potatoes boiled fo r 5-6 min in water with0.22% salt. Once boiled the potatoes were divided in 500 g portions to which60 mL of oil was added. Potatoes were served at room temperature, in 70 cm3glasses: a small fork was used to take the potatoes to the mouth. Samples werepresented in a balanced order coded with three digit numbers. Between samplesconsumers could drink water if they pleased. Acceptability was measured on a9-po int hedonic scale. Consumers were aware that we were interested in the oil,not the potatoes.Sensory Failure

In order to determine a criteria for sensory failure, samples with differentlevels of oxidized flavor were evaluated by both the trained sensory panel andthe consumer panel. We followed a procedure similar to the one described byFritsch et al. (1997). Samples with different levels of oxidized flavor wereprepared by storing bottled SO at 60C during 0, 15, 30, 45, 60 and 75 days.The trained panel followed the above described procedure using the unstructuredoxidized flavor scale, the consumers used the 9-point hedonic scale.


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198 G AMIREZ, G . HOUGH and A. CONTARINI

Shelf-lifeIn measuring the shelf-life of SO, two variation factors were considered:

storage temperature and illumination, resulting in a pxq factorial design:(1) storage temperature: 35, 45 and 60C nd(2) illumination condition: dark and 12 h/day illumination.

The high storage temperatures were chosen because we could not afford thetime necessary to store the samples at lower temperatures. The illuminationconditions were chosen considering that bottled SO can be kept in theircardboard boxes, that is, in the dark, or on supermarket shelves exposed toartificial illumination. This last condition was simulated by illuminating thebottles with a 18W fluorescent tube placed in the ovens for 12 h/day. Samplesnot to be illuminated were placed in the same ovens wrapped in aluminum foil.Prior to sensory analysis the bottles were shaken to make the contents uniform.

Samples were taken every 7 to 10 days for a total of 129 days, 92 days and57 days, for 35,45 and 60C storage temperatures, respectively. Control sampleswere stored at 4C in the dark to prevent sensory changes.

At each sensory session samples corresponding to a storage temperature andtime combination were analyzed. First assessors tasted a control sample whichthey marked as having no oxidation flavor. Then they tasted samples stored inthe dark by duplicate, light exposed samples by duplicate and a blind control.Order of presentation was at random.

RESULTSMonitoring of Assessors

A two way (Assessor x Sample) analysis of variance (ANOVA) showed asignificant(P


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SENSORY SHELF-LIFE OF SUNFLOWER OIL 199

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ivZ Ez z3 5 5UvZ28m

u 3

1

Sensory FailureIt was expected that increased oxidized flavor would lower acceptability.This was the case for the majority of the consumers, but the correlation for 9out of the 60 was unexpected as shown in Fig. 1. The more oxidized thesample, the more they liked it. It would not be reasonable to establish a shelf-life taking into account the idiosyncratic responses of these 9 consumers, as theywould contribute to increase the sensory failure point beyond that which wouldbe acceptable to the majority of the consum ers. The results of these 9 consumerswere not included in the sensory failure calculations.

R =0.90

With the remaining 51 consumers the following procedure was followed:(1) A two way ANOVA was performed considering samples and consumers asvariation factors. From this ANOVA, Fishers LSD test was used toseparate means at the 5 significance level. This value was subtracted from


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200 G. R A M kE Z , G . HOUGH and A. CONTARINI

the average acceptability score given to the fresh control sample by the 51consumersAverage acceptability of control sample LSD = 6.5 - 0.7 = 5.8.This value of 5.8 was used as the consumers sensory failure.

(2) Figure 2 shows the regression of consumers acceptability scores versusoxidation flavor scores given by the trained panel to the same samples.Entering with an acceptability value of 5.8, the oxidation sensory failurewas estimated as 3.6 on the 0 to 10scale. This value was used to estimateshelf-life as shown below.

8

7

R = 0.94=2 5W

q 4

3

sensory failure21

1 2 3 4 5 6 7 8 9 10OXIDIZED FLAVOR

FIG. 2. AVERA GE ACCEPTABILITY OVER 51 CONSUM ERS VERSUS OXIDIZEDFLAVOR SCORED BY A TRAINED PANELShelf-life

To illustrate the data obtained, oxidation flavor versus storage time forsamples stored at 45C exposed to light 12 h/day (Fig. 3) and kept in the dark(Fig. 4), are shown. Linear regressions with their correspondingWorking-Hotelling 95 confidence intervals (Drapper and Smith 1981)werecalculated to estimate shelf-lives considering the sensory failure value of 3.6


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202 G. RAMiREZ, G. HOUGH and A. CONTARINI

obtained above. Labuza (1982) reported that plotting log (days of shelf-life)versus temperature gives a straight line for most food products; this regressionwas used to estimate shelf-life at a room temperature of 20C.

For samples exposed to light, estimated shelf lives are in Table 1. Forsamples kept in the dark, shelf-life estimation at 35C was not possible assamples were far from sensory failure within the storage time considered. At45C, the samples did not reach sensory failure by the end of the experiment, butextrapolation seemed reasonable see Fig. 4). To be on the safe side, the lowerlimit of 102days was taken. Shelf-life at 60C was = 24 days, and consideringthe shelf-life at 45C = 102days; a rough estimate of the shelf-life at20C wouldbe 1140 days.

TABLE 1.TEMPERATURES AND EXPOSED TO LIGHT 12 H/DAYDAYS O F SHELF-LIFE OF SUNFLOWER OIL STORED AT DIFFERE NT

Temperature 95 Lower Estimated 95 Upper Correlation0 Lim it She lf-life Lim it Coefficient(a)20 b) 28 1 (b)35 75 91 119 0.8545 49 60 16 0.9360 (C) 17 35 0.81

(a)(b)(c)

Correlation coefficient of linear regression of oxidized flavor versus storage time.Shelf-life was estimated at this tem perature from log (shelf-life) versus temperatureLower limit was below time = 0 days.

CONCLUSIONS(1) One of the sensory assessors who was successfully screened, did not

perform satisfactorily during prolonged testing of oil, thus continuedmonitoring was necessary.

(2) A group of 9 out of 60 consumers were detected who actually preferredoxidized samples. They were not included in the sensory failure calcula-tions.3) A sensory failure point of 3.6 on a 0 to 10 oxidized flavor scale wasdetermined by correlating consumer acceptability scores versus trained panelscores.


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SENSORY SHELF-LIFE OF SUNFL OWER OIL 203

4) Light exposure significantly lowered the shelf-life of SO. Estimated shelflives at 20C were 281 days for light exposed oil, and greater than the 2years given to SO by most companies in Argentina.

REFERENCESAOCS. 1989. Flavor panel evaluation of vegetable oils. AOCS RecommendedPractice Cg 2-83, AOCS, Champaign, Illinois.DRAPPER, N.R. and SMITH, H. 1981. Fitting a straight line by least squares.In Applied Regression Analysis pp. 1-69, John W iley Sons, New York.FRITSCH, C.W. and VICKERS, M. 1997. Shelf-life of sunflower kernels. J.Food Sci. 62, 425-428.GACULA JR., M.C. 1975. The design of experiments for shelf life study. J.Food Sci. 40, 399-403.ISO. 1993. Sensory analysis. General guidance for the selection, training andmonitoring of assessors, pp. 1-15, I S 0 8586-1.KIRITSAKIS, A. K. 1998. Packaging and bottling of olive oil. In Olive oil pp.

217-220, Food & Nutrition Press, Trumbull, Connecticut.LABUZA, T.P. 1982. ShelfLife Dating ofFoods pp. 41-87,54-58, 135-139,Food & Nutrition Press, Trumbull, Connecticut.MARTfNEZ, C., MUCCI, A., SANTA CRUZ, M.J., HOUGH, G. andSANCHEZ, R. 1998. Influence of temperature, fat content and packagematerial on the sensory shelf-life of a commercial mayonnaise. J. SensoryStudies 13 331-346.MUROZ, R. 1997. Girasol 1997198. Panorama Agrario Mundial. InstitutoNacional de Tecnologia Agropecuaria (Buenos Aires, A rgentina) 21 199),NAWAR, W.W. 1996. Lipids. In Food Chemistry (O.R. Fennema, ed.) pp.3-10.

299, Marcel Dekker, New York.S.M. 1994. Changes in sensory quality of sterile cantaloupe dice stored incontrolled atmospheres. J. Food Sci. 61, 847-851.PASTOR, M.V., COSTELL, E., IZQUIERDO, L. and DURAN, L. 1996.Perfil Descriptivo de nktares de melocotdn. Evaluacidn de jueces y deatributos con el Andisis Procrustes Generalizado. Food Sci. Technol.Intern. 2, 219-230.MATTILASANDHOLM, T. and HYVONEM, L. 1995. Modifiedatmosphere-packed marinated chicken breasts and rainbow trout quality asaffected by package leakage. J. Food Sci. 60, 667-672, 684.

OCONNER-SHAW, R.E., RO BERTS, R., FO RD, A.L. and NOTTINGHAM,

RANDELL, K., AHVENAINEM, R., LATVA-KALA, K., HURMR, E.,


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