Comparison of the Frying Performance of Market Samples of Palm Olein, Corn Oil and Soya Oil in Malaysia

Transcription

1 Pertanika (5), (987) Comparison of the Frying Performance of Market Samples of Palm Olein, Corn Oil and Soya Oil in Malaysia M.A. AUGUSTIN \ K.H. LEE ] and K.T. YAU department of Food Science, Faculty of Food Science and Biotechnology, Universiti Pertanian Malaysia, 434 Serdang, Selangor Darul Ehsan, Malaysia. Palm Oil Research Institute of Malaysia, P.O. Box 6, 57 Kuala Lumpur, Malaysia. Key words: Frying performance; palm olein; corn oil; soya oil. ABSTRAK Prestasi penggorengan 3 jenis minyak yang dipasarkan di Malaysia iaitu minyak kelapa sawit olein, minyak jagung dan minyak kacang soya, dibandingkan. Kajian ini melibatkan penggorengan kepingan ubi kentang secara tidak berterusan untuk setiap Vzjam dalam masa 5 jam sehari selama 4 hart berturut-turut. Penganalisisan minyak telah menunjukkan bahawa semasa proses penggorengan berlaku: (i) pengoksidaan asid lemak tak tepu seperti yang ditunjukkan oleh perubahan-perubahan dalam nilai iodin dan komposisi asid lemak, kurang dalam minyak kelapa sawit olein berbanding dengan minyak jagung dan minyak soya, (it) pembentukan polimer kurang dalam minyak kelapa sawit olein daripada minyak jagung dan soya, (Hi) kadar perubahan nilai asid adalah lebih tinggi dalam minyak kelapa sawit olein dan (iv) selepas 4 hart minyak jagung mempunyai warna yang paling cerah. ABSTRACT The frying performance of market samples of palm olein, corn and soya oils sold in Malaysia were compared. The oils were used for intermittent frying of potato slices at half hour intervals for a period of5hr per day for four consecutive days. Analyses of oils showed that during drying (i) the oxidation of unsaturated fatty acids, as shown by changes in iodine value and the fatty acid composition, was less in palm olein than in corn and soya oils, (ii) polymer formation was least in palm olein compared to corn and soya oils, (Hi) the rate of change in acid value was highest in palm olein and (iv) that after 4 days of frying, corn oil had the lightest colour. INTRODUCTION A major proportion of edible oils is used in deepfrying operations which is one of the most common methods of food preparation. The frying performance and quality of the oil under frying conditions are of interest to oil processors, commercial fry operators and individual consumers. During frying operations, oil is continuously or repeatedly exposed to high temperatures in the presence of air and moisture. Under these conditions, hydrolysis and both thermal and oxidative decomposition take place. Degradation of the fat results in the formation of volatile and non-volatile decomposition products. Among some of the physical and chemical changes that occur during frying are increased smoking, foaming, colour and viscosity and the formation of free fatty acids, hydroperoxides, carbonyls and other products of secondary oxidation and high molecular weight polymerized compounds. (Chang et at., 978; Fritsch, 98; Roth and Rock, 97). The overuse of frying oils affects

2 MA. AUGUSTIN, K.H. LEE AND K.T. YAU the flavour, stability, colour and texture of fried food. The nutritional value and safety of the oil can also be affected (Alexander, 978). A number of frying oils, both locally produced and imported, are available in the Malaysian market., the liquid fraction of palm oil, is the major cooking oil produced locally. Corn and soya oils are among two of the more popular types of imported frying oils in the market. The prices of these oils in the local market vary, with the imported oils being more expensive than the locally produced palm olein. There has been no study on the performance of local market samples. It was thus of interest to compare the quality of palm olein, soya and corn oils during frying. It should be noted that this study was limited to the evaluation of market samples of frying oils available at local outlets only. MATERIALS AND METHODS Materials Random samples of refined, bleached and deodorized palm olein, corn oil and soya oil were bought at the supermarket. The oils for each batch were bought about a week before the start of the frying experiment. The same brand for each oil was used each time. Potatoes used in frying experiments were also from a local distributor and similar varieties could not be assured for each frying trial. Different varieties were used for all three trials. The potatoes were bought a few days prior to each frying trial. The potatoes were peeled and sliced to a thickness of mm using a mechanical slicer and slightly blotted dry prior to frying. Frying Experiments Fryings were done in Valentine Fryers. Four kg oil was heated up to 8 C in min and fryings were started half hour after the temperature of the oil had reached l"8 C. One hundred gm potato slices were fried for 3 minutes at.5hr intervals for 5hr per day for four consecutive days. This is equivalent to fryings a day. The fryer was left uncovered during the frying period. At the end of each day, loog oil was removed from the fryer and kept in a cold room at 6 C until the day of analysis. The lid of the fryer was then put on and the oil was allowed to cool overnight. The fryings were continued the next day. Analysis of Oils The peroxide and p-anisidine values of the oils were determined before the start of the experiment. Other analyses of oils were completed within three weeks after frying. The peroxide and iodine values were determined according to AOCS methods (AOCS, 974). IUPAC methods were used for the assessment of acid and />-anisidine values (IUPAC, 979). The fatty arid profile of the oil was determined by gas chromatography after preparation of methyl esters (Christopherson et al., 969; Timms, 978). The gas chromatograph was fitted with a % SP 33 column and a Flame Ionization Detector. The injector and detector temperatures were 5 C while the column temperature was 9 C. The flow rate of the carrier gas was 4ml/min. The % polar components was determined by column chromatography (Billek et al., 978) while polymer content was determined according to the method of Peled et al. (975). The dielectric constant was measured on a Food Oil Sensor (NI-, Northern Instruments). The instrument was calibrated with standards provided by the supplier. Colour was measured in a " cell in a Lovibond Tintometer. The initial oil was also screened for the presence of the antioxidants BHA, BHT and TBHQ using high pressure liquid chromatography. The method used for extraction and determination of antioxidants was based on that by Kirleis and Stine (978) and Page (979). RESULTS AND DISCUSSION Characteristics of the Fresh Oils The quality characteristics of the fresh oils are given in Table while the fatty acid composition of the oils are given in Table. The fatty acid composition of all samples of palm olein are within the range for Malaysian palm olein (Tan and Oh; 98). The fatty acid composition of all samples of corn and soya oil are within the respective ranges that were tentatively adopted by the Food and -Agricultural Organization/ World Health Organization Codex Alimentarius 96 PERTANIKA VOL. NO. S, 987

3 COMPARISON OF THE FRYING PERFORMANCE OF SAMPLES OF PALM OLEIN, CORN OIL & SOYA OIL TABLE Quality characteristics of the fresh oib Quality characteristic Batch Peroxide value (meq/kg) p-anisidine value Acid value (mg KOH/g) Each value in the table represents the mean value of duplicate analyses. The error in peroxide value, /> anisidine value and acid value were less thano.5meq/kg,.5 and.mg KOH/g oil and respectively. TABLE Fatty acid composition of the oils Type of oil Batch Days of frying C6: C8: C8:l C8: C8:3 Others Day , S PERTANIKA VOL. NO. 3,

4 MA. AUGUSTIN, K.H. LEE AND K.T. YAU TABLE (Cont.) Fatty acid composition of the oils Type of oil Batch Days of frying C6: C8: C8:l C8: C8:3 Others Day , , Day S Each value in the table represents the mean value of duplicate analyses. The mean differences in fatty acid composition in duplicate analysis were less than.3%. It should be noted that the data gives the fatty acid composition of glyceride bound fatty acids as the method used for esterification only esterifies glyceride bound and not free acids, " " indicates not detectable. Committee for Fats and Oils (Spencer et ai, 976). The peroxide, p-anisidine and acid values of RBD olein were meq/kg,.6-.9 and.5-.mg KOH/g oil respectively. The low oxidation values and acid value of RBD olein showed that the oils were of good quality. The acid value of corn oil was comparable to that of palm olein. The acid values of soya oil were between.7-.33mg KOH/g oil. The peroxide values of corn and soya oils were meq/kg and.4-4.6meq/kg respectively while the corresponding ^-anisidine values were and.-.7. The results showed that these market samples of corn and soya oils had higher oxidation values than samples of the commercial brand of palm olein used in these experiments. It should be noted that these corn and soya oils are imported into Malaysia while palm olein is produced locally. The higher oxida- 98 PERTANIKA VOL. NO, 3, 987 tion values of the corn and soya oils are probably the result of the greater degree of handling, transportation and storage of these imported oils compared to palm olein. Reference to work on oils carried out in the U.S. showed that peroxide value of commercial fresh soya and corn oils were.3meq/kg and.46meq/kg respectively (Carlson and Tabacch, 986). The results of HPLC analyses showed that all samples of corn oil contained BHA while all samples of soya oil contained TBHQ,. No antioxidants were found in palm olein. A check with the company producing the brand of palm olein used in these experiments confirmed that no antioxidants had been added to the oil. Although the oxidation values of the fresh oils were different and both corn and soya oils had antioxidants while palm olein had no antioxidants, the experiments were nevertheless

5 COMPARISON OF THE FRYING PERFORMANCE OF SAMPLES OF PALM OLEIN, CORN OIL & SOYA OIL carried out as the study was aimed at evaluating market samples of these oils available in Malaysia. Quality Changes in Oils During Frying Table gives the fatty acid composition of the fresh and used oils. The quality changes in palm olein, corn and soya oils used for frying are given in Table 3. Iodine Value and Fatty Acid Composition: The changes in iodine value of the three batches of oil after four days of frying were for palm olein, for corn oil and for soya oil. The smaller change in iodine value in palm olein compared to that of corn and soya oils indicated that less oxidation of unsaturated fatty acids has taken place in palm olein. The fatty acid composition of the oils before and after frying (Table ) also showed that lesser amounts of unsaturated fatty acids were oxidized in palm olein than in corn and soya oils. Similarly, the smaller change in iodine value in batch of corn oil compared to the other two batches also reflects the lesser extent of oxidation of C8: in this batch of corn oil. This trend was also evident in soya oil. The changes in iodine value and the fatty acid composition showed that during frying, there was a similar degree of oxidation in soya oils (Batches and 3) although they had different initial peroxide value of 4.6 and.4meq/kg. In contrast, soya oils (Batches and ) with more similar initial peroxide values of.85 and 4.6meq/kg had experienced different rates of oil deterioration during frying. The p-anisidine values for all the soya oil samples were similar. It is interesting to note these points although the reasons for them are unclear. Different rates of oil deterioration were also found in corn oil (Batches and ) although the oxidation values of the initial oils were similar. The different rates of oxidation in oils with similar initial oxidation values, was evidenced not only by the analyses of iodine values and fatty acid composition but also by the results of percentage polar components, polymer content and dielectric constant (Table 3). Polar Components and Dielectric Constant: The percentage polar components in palm olein, corn oil and soya oil after four days of frying were %,.7-3.7% and % respectively. The corresponding average changes in percentage polar components were 8.6%, 3.4% and 4.% respectively. The average changes in dielectric constant were between for all the oils after four days of frying. Billek et ai (978) states that frying oil with 7% or more polar components should be discarded. The results showed that most of the oil samples had reached the end of their useful frying life after four days of intermittent frying. The dielectric constant has been used as a quick method for monitoring oil deterioration (Fritsch, 979). However, Paradis and Nawar (98) cautioned that the dielectric constant reading may not indicate the quality of the oil. Fresh fats differ in dielectric constant and artefacts present in the frying fat such as water or fat extracted from the fried food can affect the readings. The correlations between % polar components and dielectric constant for each of the oils used are given in Table 4. The results show that there are significant correlations between % polar components and dielectric constant for each of the batches of the three types of oils although the regression equations which describe this relationship are different. Polymers: The results showed that there was a higher percentage of polymers in corn and soya oils than in palm olein after four days of frying (Table 3). No polymers were detected in any of the fresh samples of oil used. The formation of polymers is believed to require the presence of conjugated dienes (Kappelmeir, 933). As evidenced by the changes in iodine value (Table 3), the more unsaturated oils, corn and soya oils, experienced a faster rate of oxidation of unsaturated fatty acids than palm olein. The conjugated dienes are the primary oxidation products of unsaturated fatty acids and thus it may be expected that a higher rate of oxidation of fatty acids results in a faster rate of formation of polymers. Experiments on the frying performance of peanut oil, which is also more unsaturated than palm olein, also showed a faster formation of polymers in peanut oil than in palm olein (Bracco etai, (98). Acid Value: The changes in acid value in PERTANIKA VOL. NO. 3,

6 M.A. AUGUSTIN, K.H. LEE AND K.T. YAU TABLE 3 Quality characteristics of oils used for frying Type of oil Day of frying Batch Quality characteristic Batch Batch 3 Iodine value Polar components (%) S Day Dielectric constant Palm oil Day Not determined Not determined Not determined.6 Polymer content (%).9. 3 PERTANIKA VOL. NO. 5, 987

7 COMPARISON OF THE FRYING PERFORMANCE OF SAMPLES OF PALM OLEIN, CORN OIL & SOYA OIL TABLE 3 (Cont.) Quality characteristics of oils used for frying Type of oil Day of frying Batch Quality characteristic Batch Batch 3 Polymer content (%) Acid value (mg KOH/g oil) Lovibond colour ( M cell).8y,.4r 3.5Y,.6R 4.Y,.6R 5.Y,.6R 6.6Y,.8R.Y,.R.7Y, 4.3R.4Y,.3R.7Y,.4R 4.Y,.5R.4Y.3Y.7Y,.4R 4.6Y,.6R.7Y,.3R 3.Y,.4R 3.6Y,.5R 4.3Y,.5R 5.9Y,.6R.Y,.R.7Y,.3R 3.Y,.4Y 4.Y,.5R 5.5Y,.7R.4Y.3Y 4.Y,.5R 6.4Y,.7R.8Y,.4R 3.3Y,.5R 3.6Y,.5R 4.5Y,.6R 6.3Y,.8R.Y,.R.7Y,.3R.4Y,.4R 3.7Y,.5R 4.4Y,.7R.4Y.3Y 3.8Y,.5R 5.6Y,.7R Each value represents the average of duplicate analyses. The average difference between the results of duplicate analyses were. for iodine value,.6% for polymer content,.4% for percentage polar components and.mg KOH/g oil for acid value. palm olein after four days of frying were greater than that in soya and corn oils. Changes in acid value were least in corn oil during 4 days of frying (Table 3). It should be noted that the acid value is a measure of the acidic components in the oil. Increased acidity levels can be dqe to the formation of free fatty acids resulting from hydrolysis of the fat as well as oxidative chain PERTANIKA VOL. NO. 3, 987 3

8 MA. AUGUSTIN, K.H. LLE AND K.T. YAU TABLE 4 Correlations between % polar components and dielectric constant Type of oil Batch Regression equation Correlation coefficient y = 6.466x +.79 y = 6.798x -.98 y = 8.37x y m 9.43x y = 8.49x y = 7.75x ***.99***.99***.99***.99**.97** H Five pairs of values were used for calculation of each regression equation. denotes significance at. level and *** denotes significance at. level. cleavage reactions (Sims and Stahl, 97). An increased rate of formation of acids is undesirable (Wurziger, 97). Acidity is one of the factors that contributes to increased smoking during frying. Smoking is considered undesirable. Colour: The initial colour and changes in oil colour during frying are given in Table 3. The colour of fresh samples of palm olein were darker than those of corn and soya oils. It should be noted that palm olein did not contain any added phenolic antioxidants whereas corn oil had BHA and soya oil had TBHQ. The oxidation of phenolic antioxidants in the presence of heat and metals results in the formation of quinoid compounds (Lundberg, 96) which lead to colour formation. Despite the absence of added phenolic antioxidants, the colour of palm olein after hour days of frying was darkest compared to corn and soya oils. Overall Assessment of Frying Oils: Although only three market samples of each type of oils were used, the results nevertheless showed that (i) the rate of oxidation of unsaturated fatty acids, as shown by the changes in iodine value and the fatty acid composition, was slower in palm olein than in corn and soya oils and (ii) polymer formation was least in palm olein as compared to corn and soya oils. It was also evident that the acid value of palm olein was higher than that of corn and soya oil. However, the analysis of percentage polar components showed that generally all oils had reached the end of their useful frying life after four days of frying. It should be borne in mind that all the parameters used in this study are indicators of the state of oil deteriorations. Although no one parameter can judge frying life adequately in all situations, the analyses of percentage polar components is considered to be one of the more reliable indicators of the state of oil deterioration (Fritsch, 98). In 973, The German Society for fat research proposed that "A used frying fat is deteriorated if, without any doubt, colour and taste are not acceptable; if, in case of a doubtful sensory assessment, the concentration of petroleum ether insoluble oxidized fatty acids is.7% or higher and if the smoke point is lower than 7 C, the concentration of petroleum ether insoluble oxidized fatty acids is.% or higher" (Billek et al, 978). A value of.% petroleum ether insoluble oxidized fatty acids was found to correspond with 7% polar components (Billek et al, 978). Based on the results obtained for Batches and 3 and the assumption that % polar components is the most reliable indicator of frying fat deterioration, it can be seen that palm olein reached the end of its frying life after 4 days of frying whereas corn and soya oils had deteriorated beyond the acceptable limit of 7% polar components after 3 days of frying under the conditions used. This represents at least a 5% saving for palm olein if oil is discarded when it reaches the 7% polar components level. It should be appreciated that in these experiments, the oil was not replenished. In commercial frying operations, the oils is "topped-up" with fresh oil. In addition, the surface area to volume ratio of the oil has an effect 3 PERTANIKAVOL. NO. S, 987

9 COMPARISON OF THE FRYING PERFORMANCE OF SAMPLES OF PALM OLEIN, CORN OIL & SOYA OIL on oil deterioration, with rates of deterioration being faster at higher surface area to volume ratios. Thus it may be expected that the rate of deterioration of frying oil is different under the conditions of our study. Nevertheless, it gives an indication of the relative rates of deterioration of the oils. In addition to the quantitative analyses of the oils, observations made during fryings showed that foam formation was more obvious in corn and soya oils than in palm olein. Sticky films, presumably polymers were also formed on the walls of the fryers with soya and corn oils. Off-odours were very noticeable in soya oil systems during heating up of the oils prior to frying during the later days of frying. It was also noted that although the colour of palm olein was darkest compared to corn and soya oils, the crisps fried in palm olein had a similar colour to those fried in corn and soya oils. CONCLUSION This study shows that the market samples of palm olein, corn and soya oils undergo different rates of oil oxidation and hydrolysis. Judgement of frying oil quality based on the test for percentage polar components shows that four days of frying under the conditions of the experiment generally causes the oils to deteriorate to a point beyond the maximum tolerable limit for use. The disadvantages of palm olein as compared to corn and soya oils are the higher acid value and darker colour of the used oils, but its advantages are the lower rate of oxidation of unsaturated fatty acids and the lower rate of formation of polymers. From a user point of view, an additional advantage of palm olein is the easier cleaning of fryers, as the sticky films formed on the walls of fryers in corn and soya oil systems are hard to remove. Furtermore, palm olein has a lesser tendency to foam than corn and soya oils. It should be noted that in this study, the three random samples of each type of oil was bought at retail outlets. There was no control over the initial characteristics of the oils and the presence of antioxidants in the oils. Both corn and soya oils had the advantage of having antioxidants but the initial quality characteristics of palm olein were better than of corn and soya oils. These factors may have an effect on the rates of oil deterioration and thus the results of this study are only applicable to the local edible oil scene. ACKNOWLEDGEMENTS The authors would like to thank the Palm Oil Research Institute of Malaysia for sponsoring the research. Thanks are also due to Prof. A.S.H. Ong for his helpful comments. REFERENCES ALEXANDER, J.C. (978): Biological effects due to changes in fats during heating. / Amer. Oil Chem. Soc. 55:7-77. AOCS. (974): Official and Tentative Methods of the American Oil Chemists' Society, Champaign, IL, USA, Srdedn. BRACCO, U., A. DIFFENBACHER and L. KOLAROVIC. (98): Frying performance of palm oil liquid fractions./ Amer. Oil Chem. Soc, 58: 6 -. BILLEK, G., G. GUHRandJ. WAIBEL. (978): Quality assessment of used frying fats. / Amer. Oil Chem. Soc, 55: CARLSON, B.L. and M.H. TABACCH. (986): Frying oil deterioration and vitamin loss during food service operation./ Food Sri., 5: 8-3. CHANG, S.S., RJ. PETERSON and C.T. Ho. (978): Chemical reactions involved in the deep-fat frying of foods./ Amer. Oil Chem. Soc, 55: CHRISTOPHERSON, S.W. and R.L. GLASS. (969): Preparation of milk fat methyl esters by alcoholysis in an essentially non-alcoholic solution. / Dairy Sci., 5:89-9. FRITSCH, C.W., D.C. EGBERG and J.S. MAGNUSON (979): Changes in dielectric constant as a measure of frying oil deterioration. / Amer. Oil Chem. Soc. t 56: FRITSCH, C.W., D.C. EGBERG and J.S. MAGNUSON. (979): Changes in dielectric constant as a measure of frying oil deterioration. / Amer. Oil Chem. Soc, 56: lupac. (979): Standard Methods for the analysis of oils, fats and derivatives. (Paquot, C. ed.). IUPAC App. Chem. Div., Commission on oils, fats and derivatives, 6th edn. KAPPELMEIR, C.P.A. (933): Farben-Ztq, 36, 8, 77 through Bailey's Industrial Oil and Fat Products (Swern, D. Ed.), Vol., 979, pg KIRLEIS, A.W. and CM. STINE. (978): Retention of synthetic phenolic antioxidants in model freezedried food systems./ Food Sci. 43: PERTANIKA VOL. NO. 3,

10 MA. AUGUSTIN, K.H. LEE AND K.T. YAU LUNDBERG, W.O. (96): "Autoxidation and Antioxidants", Vol., Interscience Publishers, New York, p. 5. PAGE, B.D. (979): High Performance liquid chromatographic determination of nine phenolic antioxidants in oils, lard and shortening. /. Assoc. off Anal Chem, 6: PARADIS, A.J. and W.M. NAWAR. (98): Evaluation of new methods of assessment for used frying oils. / Food Sci., 46: PELED. M., T. GUTFINGER and A. LETAN. (975): Effect of water and BHT on the stability of cottonseed oil during frying. J. Sci. Food Agric, 6: ROTH, H. and S.P. ROCK. (97): The chemistry and technology of frying fat. I. Chemistry, The Bakers Digest, (August): SIMS, R.J. and H.D. STAHL. (97): Thermal and Oxidative Deterioration of frying fats. The Bakers' Digest, (October): 5-5. SPENCER, G.F., S.F. HERB and PJ. GORMISKY. (976): Fatty acid composition as a basis for identification of commercial fats and oils. / Amer. Oil Chem. Soc, 53: TAN, B.K. and F.C.H. OH. (98): Oleins and stearins from Malaysian palm oil Chemical and Physical characteristics. PORIM TechnoL, Palm Oil Research Institute of Malaysia, No. 9. TiMMS, R.E. (978): Artefact peaks in the preparation and gas-liquid chromatography of methyl esters. Aust.J. Dairy Tech., 33: 4-6. WURZIGER, J, (97): Analytical control and evaluation of used frying fats. In: 'Symposium on deep frying fats' (Symposium uber Fritturefette) (Auerswald, A.; Brandsletter, B. Eds.). Vienna, Austria, May 97. (Received June, 987) 34 PERTANIKA VOL. NO. 3, 987