COMPARATIVE STUDIES ON PHYSICAL PROPERTIES OF VEGETABLE OILS AND THEIR BLENDS AFTER FRYING N.S. SUSHEELAMMA, M.R. ASHA, R. RAVI and A.K. VASANTH KUMAR Department of Sensory Science, Central Food Technological Research Institute, Mysore - 570013, India Received for Publication February 29,2002 Accepted for Publication July 9, 2002 ABSTRACT Physical properties of six commonly used oils and three blends consisting of three oils in each blend were studied after three successivefrying of 'poories ' @zed snackpom flattened dough of refined wheatflour). The changes in viscosity, CIE trans-reflectance color and related parameters, UV-Visible spectra and UV- spectra of oil samples in solvent system (ch1oroform:methanol; 2:1, v/v) were studied. l%eresults showed that viscosity and color of the oils changed to a much higher extent after first firing than subsequent fiyings. The hue angle followed a similar trend. Changes in the UY-spectra in the solvent system indicated an increase in the formation of conjugated compounds after successive fryings. Peroxide values (Pv) also increased afterf v i n g . Principal Component Analysis (PCA) plots of the data indicated that among oils examined groundnut oil and soy oil in Combination with other oils were preferred forfrying. Use of small amounts of unrefined oils Cfiltered) such as mustard oil or sesame oil which have a high content of natural antioxidants was beneficial as formation of conjugated compounds and increase in peroxide value was minimized affer successive frying using blended oils. 'Corresponding author: Department of Sensory Science, Central Food Technological Research Institute, Mysore - 570013, India. TEL: 0091-821-515842; FAX: 0091-821-517233; E-mail: [email protected]Journal of Food Lipids 9 (2002) 259-276. All RighfsReserved. "Copyright 2002 by Food & Nutrition Press, Inc.. Trumbufl,Connecticut 259
Transcript
COMPARATIVE STUDIES ON PHYSICAL PROPERTIES OF VEGETABLE OILS AND THEIR BLENDS AFTER FRYING
N.S. SUSHEELAMMA, M.R. ASHA, R. RAVI and A.K. VASANTH KUMAR
Department of Sensory Science, Central Food Technological Research Institute,
Mysore - 570013, India
Received for Publication February 29,2002 Accepted for Publication July 9, 2002
ABSTRACT
Physical properties of six commonly used oils and three blends consisting of three oils in each blend were studied after three successivefrying of 'poories ' @zed snackpom flattened dough of refined wheat flour). The changes in viscosity, CIE trans-reflectance color and related parameters, UV- Visible spectra and UV- spectra of oil samples in solvent system (ch1oroform:methanol; 2:1, v/v) were studied. l%e results showed that viscosity and color of the oils changed to a much higher extent after first firing than subsequent fiyings. The hue angle followed a similar trend. Changes in the UY-spectra in the solvent system indicated an increase in the formation of conjugated compounds after successive fryings. Peroxide values (Pv) also increased after fv ing . Principal Component Analysis (PCA) plots of the data indicated that among oils examined groundnut oil and soy oil in Combination with other oils were preferred forfrying. Use of small amounts of unrefined oils Cfiltered) such as mustard oil or sesame oil which have a high content of natural antioxidants was beneficial as formation of conjugated compounds and increase in peroxide value was minimized affer successive frying using blended oils.
'Corresponding author: Department of Sensory Science, Central Food Technological Research Institute, Mysore - 570013, India. TEL: 0091-821-515842; FAX: 0091-821-517233; E-mail: [email protected]
Journal of Food Lipids 9 (2002) 259-276. A l l Righfs Reserved. "Copyright 2002 by Food & Nutrition Press, Inc.. Trumbufl, Connecticut 259
260 N.S. SUSHEELAMMA, M.R. ASHA, R. RAVI and A.K. VASANTH KUMAR
INTRODUCTION
During heating such as fiying of food products, oils or fats undergo hydrolysis, thermal degradation, oxidation and polymerization. These are enhanced if the fat/ oil contains highly unsaturated fatty acids, whch result in changes in both physical and chemical properties. In order to minimize these changes, hydrogenation, partial hydrogenation, addition of antioxidants or other oils which have lower content of highly unsaturated fatty acids have been attempted (Ewans et al. 1972; Dobbs et al. 1978). Thus, addition of corn oil to canola oil or partial hydrogenation of canola oil and soybean oil (Eskin et al. 1996) has been found beneficial in extending the shelf-life of the oils. The blending of oils has been encouraged in the recent past and it is gaining importance on nutritional basis, thus blended oils have been used for frying purposes (Nasirulla et al. 1991; Murthy et al. 1987; Stevensen et al. 1984; Yen 1991; Premavalli etal. 1998; Prakashet al. 2001). Blending ofthree oils was attempted for the frrst time and three such blends were prepared with commonly used vegetable oils. Some of the changes in physical properties studied in model experiments after successive frying are reported in this paper.
MATERIALS AND METHODS
Oils and Blends
Sunflower, coconut, soybean, groundnut, sesame and mustard oils were obtained from a local market in Mysore. Unrefined oils were used to retain their tocopherols and natural antioxidants, except for sunflower and soybean oils, which were refined. Blending was done with three oils in a blend, so that 0 3 fatty acid content did not exceed 3%. The proportion of saturated fatty acid: monounsaturated fatty acids: polyunsaturated fatty acids (SFA: MUFA: PUFA) was adjusted to be close to 1.25: 1: 0.9 keeping in mind the commonly used oils in food processing, and the proportion of 0 6 and 0 3 fatty acid to be close to 8: 1 as per WHO/ FA0 ( 1995) recommendation. Of the several theoretically possible blends, three were chosen for model frying. The blends labeled ‘Q’, ‘R’ and ‘V’ consisting of three oils in each in the proportion by weight given below were prepared in triplicates and used in model frying studies.
Blend ‘Q’ - Groundnut oil: soy oi1:sesame oil as 54:25:21, Blend ‘R’ - Groundnut oil: sunflower oi1:mustard oil as 65:25:10, Blend ‘V’ - Coconut oil: sesame oi1:soy oil as 35:57:8.
COMPARATIVE STUDIES ON VEGETABLE OILS 261
Model Frying
Refined wheat flour was mixed with (50%) water and made into a dough. Balls of th~s dough weighing approximately 5 g each were flattened using a wooden pin and roller and the poories were fried in oil at the smoking point. The temperature was recorded by inserting a thermometer in the center of the oil in the pan. The frying oil was allowed to cool to room temperature and heated again for frying. Three successive fryings involving 4 h cooling phase after each frying was carried out in triplicate (for three successive days) with each individual oil and the three oil blends ‘Q’, ‘R’ and ‘V’, respectively. The peroxide value (PV) of the individual oils and their blends were determined in triplicates according to the AOAC (2000) procedure.
Viscosity
The viscosity of individual oils and three oil blends before and after successive frying was determined in triplicate using a Brookfield (WS Brookefield Engineering Company, Middleboro, MA) synchroelectric rotovisco viscometer with LVT model spindles (spindle No 1) at 25 f 1C with speeds ranging from 0.3 to 60 rpm (at shear rate of 0.01 to 3.5 ys-’). The instrument constants as provided by the manufacturers were used to calculate the viscosity values and expressed as rnPas.
Absorbance and Photometric Color Index (PCI)
The color of oils was measured using visible absorbance of the three blended oil samples before and after three successive fryings in triplicate at wavelengths of 460, 550,620 and 670 nm against 100% dichloromethane. The oil samples were filtered through a Whatman No. 1 filter paper. The ‘PCI’ was determined according to the AOCS (2000) method (Cc 13c - 50,1991) using the formula:
PCI = [ 1.2*A460 + 67.7*A550 + 41.2*A620] - [56*A670] A = absorbance at a specified wavelength
Color Measurement
The evaluation of color by the trans-reflectance measurement was also carried out using a Shimadzu UV 2100 (WS Shimadzu corporation, Kyoto, Japan) color measuring instrument with an appropriate integrating spheroid. Readings were taken using Illuminant C at a 2” observer and a slit width of 2 nm. Average of triplicate values was taken for computation. The ‘L’, ‘a’, and ‘by values under CIE lab system were recorded. Other relevant parameters such as hue angle ‘0’
262 N.S. SUSHEELAMMA, M.R. ASHA, R. RAVI and A.K. VASANTH KUMAR
(theta), ‘chroma’, total color as well as hue and color differences were also calculated (Hunter 1975).
Spectrophotometry
The spectra of individual oils and their blends in triplicate before and after three successive frying were recorded using Genesys 2 Spectronic spectrophotometer (M/s Milton Roy Co., Rochester, NY) to check their purity (Paquot and Hautfenne 1987). The UV-visible spectra of oils alone and their blends and UV spectra of individual oils and the three blends after dilution to 1% in chloroform: methanol solvent mixture (2: 1, v/v) was recorded immediately after dilution against the solvent blank. Spectra were recorded in triplicates and mean values were used for calculation of conjugated compounds according to the AOCS (1991) method Cd 7-58.
Principal Component Analysis
The results obtained from spectral data of individual oils and the three blends ‘Q’, ‘R’ and ‘V’ were subjected to principal component analysis, as multiple comparisons could be easily made between the individual oils or between the oil blends after successive frying. This would also allow evaluation of the extent to which the variations observed in the results are accounted for by the parameters studied.
Data Analysis
All the experiments were carried out in triplicate for the individual oils and the three blended oils. Mean values were taken for final computation. Statistical analysis of the data was carried out using Duncan’s multiple range test (Duncan 1955) and analysis of experimental results was carried out using Statistica ‘99 statistical software (1 999).
RESULTS AND DISCUSSION
The addition of a small amount of ghee to frying oil is practiced in many households during deep fat frying. The blending of two oils is permitted at present for frying purposes but the addition of a small amount of a third oil may be permitted only on health grounds.
In Inha, rapeseed and mustard oils are commonly used in the north and north- east regions, coconut oil in the south (Kerala and part of Tamil Nadu), groundnut and sesame in Maharashtra, Karnataka, Tamil Nadu and Andhra Pradesh, while
COMPARATIVE STUDIES ON VEGETABLE OILS 263
sunflower and groundnut oils are used in Madhya Pradesh and Bihar. Soy oil has been used in some parts of the world, but not in India. However, recently soy oil has been used in some regions in India for frying of foods. Keeping in mind the local culinary practices and consumption patterns, the changes in oils and their blends were studied in model frying.
Viscosity
The change in viscosity with shear rate for individual oils is shown in Fig. la and lb; a decrease in viscosity with increase in shear rate was observed. The values ranged from 80 to 150 mPas between 0.1 to 0.4 y/s. Below this shear rate, the values were very high. Only mustard oil showed values greater than 300 &as at 0.04 yls. The viscosity of blended oils, as shown in Fig. 2a, 2b and 2c, also showed a decrease with increasing shear rate. The values were slightly higher for blend ‘R’ as compared to blends ‘Q’ and ‘V’. All of the blends showed an increase in viscosity after first frying, a slight decrease after second frying and again an increase after third frying. The values were close to those of unheated oil in all blended oils, except for blend ‘V’ in which.it was slightly more than that of unheated oil. Very high values were recorded at very low shear rates. However, between 1 and 4 yls there was little difference, while at 0.1 to 1 yls, the differences were considerable and consistent.
THE COLOR OF OILS
Visual Appearance
Among the oils used for making up the blends, sunflower oil and coconut oil were refined and colorless, but soy oil had a pale yellow color with some greenish tint, while groundnut oil was yellow in color as it was only filtered and not refined. Sesame oil was intense yellow while mustard oil was reddish in appearance. All the blended oils ‘Q’, ‘R’ and ‘V’ appeared yellow in color.
Photometric Color Index (PCI)
Photometric color values were determined as a measure of comparing the changes in the color of oil blends to express them as a single number. The values for oil blends before and after successive frying are shown in Fig. 3. The three blends differed in their behavior as PCI of the oils decreased after the first frying in blend ‘Q’ and significantly increased after the third frying. In case of ‘R’, it
264
A
B
N.S. SUSHEELAMMA, M.R. ASHA, R. RAVI and A.K. VASANTH KUMAR
FIG. 1. VISCOSITY OF INDIVIDUAL OILS A) Coconut oil, Sunflower oil, Soya oil and B) Groundnut oil, Sesame oil, Mustard oil.
increased after the first frying, decreased slightly after the third frying. In the ‘V’ series, a similar trend was observed, but the values were lower compared to the ‘R’ series. Thus ‘PCI’ values could also be used to follow the changes in frying of oils, but this involves recording the absorption at fixed wavelengths for computation and hence it was felt necessary to study the changes in color by CIE color measuring system and also the entire spectra of oils and blends before and after successive flyings.
FIG. 2 A, B, C. VISCOSITY OF OIL BLENDS ('Q', ' R AND 'V') SYMBOLS ARE: 0, Unheated oil; 1, Oil sample after first frying; 2, After second frying and 3, After third frying,
respectively.
266 N.S. SUSHEELAMMA, M.R. ASHA, R. RAW and A.K. VASANTH KUMAR
12
10 - -
0 1 2 3 No. of fryings
0
FIG. 3. PHOTOMETRlC COLOR INDEX OF OIL BLENDS (‘Q’, ‘R’ AND ‘V’) AFTER FRYING
CIE Color Values
The plots of CIE L, a, b values for individual oils and their blends ‘Q’, ‘R’ and ‘V’ are shown in Fig. 4a. The ‘L’ values for the oils and blends ranged from 5 to 16, indicating comparable lightness. The negative ‘a’ and ‘b’ values for sunflower and coconut oils indicated colorless or very pale color. The high negative ‘a’ and positive ‘b’ value of soy oil indicated a pale greenish yellowness in color. The negative value close to zero of ‘a’ and positive value of ‘b’ for groundnut oil indicated a yellow color. Sesame and mustard oils had both positive ‘a’ and ‘b’ values, but ‘b’ value was higher for sesame indicating an intense yellow color, while ‘a’ value was quite high for mustard oil, which was red in color. All the blended oils ‘Q’, ‘R’ and ‘V’ had ‘a’ value close to zero and a positive ‘b’ value indicating a yellow color. However, ‘Q’ and ‘R’ were more intense as compared to ‘V’ with a slightly lower ‘b’ value. Blend ‘R’ had a positive ‘a’ value and blend ‘Q’ had a low negative ‘a’ value indicating a slight greenness in ‘Q’ as compared to V’, since ‘Q’ had a higher content of soy oil.
Fried Oils
After successive frying all the oil blends exhibited some common features (Fig. 4b). After the first frying, the ‘a’ value showed a tendency to decrease while after the second fiying it showed a slight increase but after the third frying it showed a
COMPARATIVE STUDIES ON VEGETABLE OILS 267
.\* ,a FIG. 4A. CIE L, a, b VALUES FOR THE OILS AND THEIR BLENDS
4B CIE L, a, b VALUES FOR BLENDED OILS (‘Q’, ‘R’ and ‘V’) AFTER FRYING Symbols are 0, Unheated oil, 1 , Oil sample after first frying, 2, After second frying and 3,
third frying, respectively After
268 N.S. SUSHEELAMMA, M.R. ASHA, R. RAVI and A.K. VASANTH KUMAR
decrease again. The ‘b’ value showed a tendency to decrease after the first and second fryings, but exhibited an increase after the third frying. The ‘L’ values varied slightly but exhibited a trend similar to that o f ‘a’ by showing an increase after the first frying, a decrease after the second frying and again an increase after the third frying. Visually, some difference in yellowness of the oil blends was observed after successive fryings. These subtle differences could be detected clearly instrumentally with a high sensitivity as compared to visual judgment, although slight differences in the intensity of yellowness were perceived.
The hue angle ‘0’ variations indicate clearly the change in yellowness of the oils (Table 1) during frying. The ‘0’ values of ‘Q’ showedgreater changes after the second frying, ‘R’ showed slight changes after the first and third fryings, while ‘V’ did not show any change after the first frying but more pronounced changes only after the third frying. The ‘chroma’ values for ‘Q’ did not show much difference after successive fryings, whde for ‘R’ it showed an increase after the first and third fryings and for ‘V’ a higher increase after the first frying was observed and this was decreased up to the third frying. The hue difference in ‘Q’ decreased after the first and second fryings, but increased after the third frying. In ‘R’, it increased after the first frying, slightly decreased after the second frying and increased after the third frying. In ‘V’, it increased after the first frying, no change after the second frying but decreased considerably after the third frying. The values for ‘total color’ and ‘hue difference’ showed a trend similar to that of ‘chroma’ values, whle subtle differences were found in ‘color difference’ values as compared to changes in ‘0’ values.
Spectra of Oils
The U V absorption region extends from 300 to 360 nm for most oils and their blends. During successive fryings, the major peaks did not show much of a difference but minor peaks showed slight increase or decrease and new shoulders appeared in some regions between 240 to 245 nm and 275 to 290 nm. A similar trend was observed for the blended oils as well.
Spectra in Solvent
The absorbance of the oils in the UV region was very high and hence U V spectra of 1 % oil were measured in chloroform : methanol (2: 1, v/v) before and after successive fryings. The individual oils did not show major changes in their peak hmax, but the absorbance showed a greater change after the first frying and marginal increase after the second and third fiyings. Blend ‘Q’ showed a major change after the first frying, but did not change much after the second and third fryings, while blends ‘R’ and ‘V’ were similar as they showed changes after the second and third fiyings; the absorbance values were, however, higher in blend ‘R’ as compared to blend ‘V’.
COMPARATIVE STUDIES ON VEGETABLE OILS 269
TABLE 1. HUE ANGLE, CHROMA, TOTAL COLOR, COLOR AND HUE DIFFERENCE VALUES OF
OIL BLENDS AFTER SUCCESSIVE FRYING
Condition Hue Chroma Total Colour Hue angle color difference difference
‘Q’, ‘ R and ‘V’ are oil blends consisting of three oils. GNO, Groundnut oil; SES, Sesame oil; SOY, Soy oil; SNF, Sunflower oil; MUS, Mustard oil; COCO, Coconut oil. 0, unheated oil; 1, oil after first
frying; 2, oil after second fiying; and 3, oil after third frying.
Means with different letters in the same column differ significantly ( R 0 . 5 ) from one another.
Relative Changes in Oil Characteristics
The changes in peroxide value, 3Lmax/Absorption maximum (Abs.max.) for the major peak, its absorbance value, area of major peak, ratio of absorbance at 2331274 nm and conjugated dienes and trienes of the individual oil samples and their blends are shown Tables 2 and 3, respectively. The oils did not show major changes in smoke points after successive fiyings. The maximum drop of 2C in smoke point was observed for sesame oil followed by groundnut, coconut and mustard oils, with no change in sunflower oil or soy oil, which were refined. The blended oils ‘Q’ and ‘R’ showed slight changes after the first firing but little or no change after subsequent fiyings, while blend ‘V’ did not show any change during successive fiyings.
270 N.S. SUSHEELAMMA, M.R. ASHA, R. RAVI and A.K. VASANTH KUMAR
TABLE 2. CHANGES IN PHYSICAL PROPERTIES OF OILS AFTER FRYING
OilSamples Condition kmax ODat P.AreaOD CD CT PV nm lmax ratio % % meqkg
Amax, absorption maxima; OD, OD at Abs.max; OD Ratio, absorbance at 233d274nm; P.Area, Peak are& CD,conjugated diene; CT, Conjugated triene, 0,Unheate.d oil; 1, Oil afiei first frying; 2, Oil after second fiymg and 3, Oil after third frying; PV, Peroxide value
Means with different letters in the same column differ significantly (Pc0.5) from one another.
The absorbance (OD) values were, however, lowest for coconut oil, slightly higher for groundnut oil and still higher for sunflower and mustard oils and yet comparable, but very high for soy and sesame oils. A maximum change was noted for all samples after the fust frying, but a continuous increase was observed for sunflower, soy and mustard oils (Table 2) indicating that the changes in OD are proportional to the content of highly unsaturated fatty acids.
In case of blended oils (Table 3), blends ‘R’ and ‘V’ showed a very little change in OD at Imax, whle blend ‘Q’ showed a significant and continuous increase after successive fryings. The area of the major peak also followed a similar changing trend after successive wings. Oils with highly unsaturated fatty acids could be used preferably with other oils which have lower unsaturation or which contain natural antioxidants so that the formation of conjugated compounds be minimized.
COMPARATIVE STUDIES ON VEGETABLE OILS 27 1
TABLE 3. CHANGES IN PHYSICAL PROPERTIES OF OIL BLENDS AFTER FRYING
Oil Blends Condition Abs.max. OD at P.Area OD CD CT PV nm lmax ratio % % rneqkg
Amax, absorption maxima; OD, OD at Abs.max; OD Ratio, absorbance at 233d274nm; P.Area, Peak area; CD,conjugated diene; CT, Conjugated triene, PV, Peroxide value; 0, Unheated oil; 1, Oil after first fiying; 2, Oil after second frying and 3, Oil after third frying; SNF, sunflower oil; COCO, coconut oil; SOY, soy oil; GNO, groundnut oil, MUS, mustard oil; SES, sesame oil.
Means with different letters in the same column differ significantly (R 0.5) from one another
Absorption Ratio
The absorption at 2331274 nm has been used as an index (Appleqvist and Kamal-Eldin 1991) of oil oxidation during alkali isomerization. However, for comparison after successive frymg of oils, similar calculations were made and the results showed that in the individual oils it decreased significantly after the first frying and remained almost unchanged subsequently in case of sunflower, soy, groundnut, mustard and coconut oils, while it showed a tendency to increase after the first and second frylngs and decreased after the third Sying in sesame oil (Table 2). In the blended oils, ‘Q’ and ‘R’ showed a tendency to decrease during frying and blend ‘V’ increased after the second and third fqings (Table 3).
Conjugated Compounds
The content of conjugated compounds formed could be detected by other physical and chemical methods, but changes in the UV spectral properties have been considered as the most powerful tool for this purpose (O’Connor 1960). Although the method is commonly used to trace the changes in oil during alkali isomerization, sesame oil and its mixtures have been reported to be an exception
212 N.S. SUSHEELAMMA, M.R. ASHA, R. R4VI and A.K. VASANTH KUMAR
to this type of calculation (Appleqvist and Kamal-Eldin 1991), an attempt was made here to use it as an index for tracing the relevant changes after successive fryings. The data, as shown in Tables 2 and 3, indicated that most oils and their blends experience an increase after successive fiying and greater changes occurred in trienes compared to dienes. In the blend oil ‘Q’, the content of both dienes and trienes was high as compared to blends ‘R’ and ‘V’.
PCA Plots of Individual Oils and Their Blends
The pattern of changes in properties of individual oils after successive fryings is shown in Fig. 5 . Some differences with respect to conjugated compounds, depending on their content and composition of unsaturated fatty acids, were observed. Coconut oil contained the lowest level of unsaturated fatty acids, but its absorbance ratio (233/274) was highest. This was followed by groundnut, mustard, sesame, sunflower and soybean oils, respectively. The content of conjugated compounds and PV were lowest for ground nut oil during repeated fryings as compared to other oils and highest in soy oil followed by sunflower oil with higher contents of unsaturated fatty acids.
PCA plots of oil blends, shown in Fig. 6 , indicate that blends ‘V’ and ‘R’ had the lowest PV and conjugated compounds after repeated fryings, and blend ‘R’ showed a higher increase as compared to ‘V’. Blend ‘Q’ had a higher PV and dienes and trienes contents. The relative increase was still lower in blend ‘V’ as compared to that of blend ‘R’, indicating that the difference in blend ‘V’ may be due to the presence of natural antioxidants in sesame oil. Antioxidant properties of sesame oil have been reported by Shankar et al. (2000).
During model frying experiments on olive oil, the nature of unsaturated fatty acids, the temperature of heating and the content of unsaturated fatty acids were found to influence the formation of oxidized compounds (Fedeli 1988). The formation of oxidized compounds was reported to increase during three different modes of heating of safflower oil (Khatoon and Krishna 1998).
The oils and their blends showed changes during frying as indicated by variations in the viscosity, color, spectral characteristics and conjugated compounds. Major changes occurred during the first frying and lesser changes during subsequent wings. Blending of oils has been attempted with three oils and though the amount of h d oil added may be small, it could minimize the formation of oxidized or conjugated compounds during deep fat frying (which is a common use for oils in the preparation of snacks) without affecting the quality of the fned product (un published results), and thus it may be advantageous. The results indicate that it is beneficial to consider mustard or sesame oil for this purpose especially for blending with soy oil, which has a high content of unsaturated fatty acids.
FIG. 5. PCA OF INDIVIDUAL OILS AFTER SUCCESSIVE FRYING SYMBOLS ARE: 0, Unheated oil, 1 , Oil sample after first frying; 2, After second frying and 3, After third frying,
respectively. Please refer to Table 2 for abbreviations.
274 N.S. SUSHEELAMMA, M.R. ASHA, R. RAVI and A.K. VASANTH KUMAR
2.5
1 .5
g OA
y 4.5
Y z a .. (Y
-1.6
- 2 1
4 I
+ - + -1 .I -1 4.5 0 0.5 1 1 .s 2
PCA 1 : 65.61%
-t- Attributes 0 Samples
FIG. 6. PCA OF OIL BLENDS AFTER SUCCESSIVE FRYING Symbols are: 0, Unheated oil; 1, Oil sample after first frying; 2, After second frying and 3, After
third frying, respectively. Please refer to Table 3 for abbreviations.
COMPARATIVE STUDIES ON VEGETABLE OILS 215
ACKNOWLEDGMENT
The authors are thankhi to D. Rajalakshmi, the former Head of Sensory Science Department and Dr. V. Prakash, Director, CFTRI for their encouragement during the course of this work.
REFERENCES
AOAC. International 2000. Association of Official Analytical Chemists. Official Methods 965.33. Official Methods of Analysis, 17" Ed., Gaithersburg, MD.
AOCS. 199 1. Official Methods and Recommended Practices of the American Oil Chemists ' Society 4" Ed., Method Cc 13c -50. American Oil Chemists Society, Champaign, IL.
AOCS. 1991. Official Methods and Recommended Practices of the American Oil Chemists ' Society 4" Ed., Method Cd 7-58. American Oil Chemists Society, Champaign, IL.
APPLEQVIST, L.A. and KAMAL-ELDIN, A. 1991. Sesame Oil and its mixtures are exceptions to AOCS method Cd 7-58. J. Am. Oil Chem. SOC. 48,693
DOBBS, J.E., VAISEY-GENSER, M. and DIAMANT, R. 1978. Unpleasant odours of rape seed oil heated to frying temperatures. Can. Inst. Food Sci.Techno1. J.
DUNCAN, D.B. 1955 .Multiple range test and multiple F tests. Biometrics, I I, 1- 42.
ESKIN, N.A.M., MCDONALD, B.E., PRZYBYLSKI, R., MALCOLMSON, L.J., SCARTH, R., MAG, T., WARD, K. and ADOLPH, J. 1996. Canola oil. In Bailey's Industrial Oil and Fat Products Edible Oil and Fat Products: Oils and Oil Seeds, Vol.11, 5th Ed., (Y.H. Hui, ed.) pp. 75-77, John Wiley & Sons, New York.
EWANS, C.D., WARNER, K., LIST, G.R. and COWAN, J.C. 1972. Room odor evaluation of fats. J. Am. Oil Chem. SOC. 49, 578-582.
FEDELI, E. 1988. Changes, new approaches. In Frying of Food Principles, (G. Varela, A.E. Bender and I.D. Morton, eds.) pp 52-81, C.H. Publications, Wemheim, Germany.
HUNTER, R.S. 1975. The Measurement of Appearance, pp. 103-1 10, Academic Press, London.
KHATOON, S. and KRISHNA, A.G.G. 1998. Assessment of oxidation in heated safflower oil by physical, chemical and spectroscopic methods. J. Food Lipids
MURTHY, T.N., SHARMA, M. and DEVDHARA, V.D. 1987. Storage stability
11, 66-70.
5, 247-267.
of edible oils and their blends. J. Food Sci. Technol. 24, 84-87.
276 N.S. SUSHEELAMMA, M.R. ASHA, R. RAVI and A.K. VASANTH KUMAR
NASIRULLA, ANKAIAH, K.N., KlUS€€NAh4URTHY, M.N. and NAGARAJA, C.V. 1991. Quality characteristics of edible vegetable oil blends. J. Am.Oil Chem. SOC. 68, 446-447.
O’CONNOR, R.T. 1960. Spectral properties. In Fatty Acids, Their Chemisv, Properties, Production and Uses, 2nd Ed., Part I, (K.S. Markley, ed.) pp. 379- 398, Interscience Publishers, New York.
PAQUAT, C. and HAUTFENNE, A. 1987.Evidence of purity and deterioration from ultraviolet specrtophotometry. In Standard Methodsfor the Analysis of Oils, Fats and Derivatives, 7th Ed. (IUPAC, Applied Chemistry Division, Commission on Oils, Fats and Derivatives) pp. 2 12-2 13, Blackwell Scientific Publications, Oxford, UK.
PRAKASH, M., RAVI, R. and BHAT, K.K. 2001. Effect of blending on sensory odor profile and physico-chemical properties of select vegetable oils. J. Food Lipids 8, 163-177.
PREMAVALLI, K.S., MADHURA, C.V. and ARYA, S.S.1998. Storage and Thermal Stability of refined cottonseed oil mustard oil blends. J. Food Sci. Technol. 35, 530-532.
SHANKAR, V.S., LOKESH, B.R. and SAMBAIAH, K. 2000. Antioxidant stability of sesame oil and its blends with other vegetable oils. 14* Indian Convention of Food Scientists and Technologists, Nov. 22-24, Mysore, India.
STEVENSEN, S.G., VAISEY-GENSER, M. and ESKIN, N.A.M. 1984. Quality control in the use of deep frying oils. J. Am. Oil Chem. SOC. 61, 1102-1 108.
Statistica ‘99, StatSoft INC. 2300 East 14* Street Tulsa, OK. WHOEAO 1995. Joint consultation: Fats and oils in human nutrition, Nutr. Rev.
