Frying Qualities of Palm Oil and Palm Olein under Simulated Deep-Fat Frying Conditions Etsuji YUKI* and Kyozo MORIMOTO* * Sanyo Women's Junior College (1-1, Sagata-honmachi, Hatsukaichi-cho, ** Hiroshima Saeki-gun, Food Hiroshima-ken) Research Institute (70-go, 12-ban, Hijiyama-honmachi, Minami-ku Hiroshima-shi) The frying qualities of palm oil and palm olein and the effects of antioxidants wer examined under simulated deep-fat frying conditions. Palm olein presented a better stability than palm oil in oxidation after frying treatment, although it was less before such treatment. The addition of silicone oil (SO) prevented glyceride from hydrolytic and oxidative deterioration and effectively decreased the loss of tocopherols and tocotrienols (Tocols) and the drop of AOM value. On the other hand, the addition of natural mixed tocopherol (NMT) was considerably effective in improving the AOM values before and after the treatment. It is therefore assumed thathe addition of SO and/or NMT is very effective in stabilizing refined, bleached and deodorized (RBD) palm oil and palm olein. 1 Introduction In these days the production and export of palm oil and its fractional products have rapidly increased in Malaysia and other countries. Palm oil and palm olein have been widely used in preparing snacks and fried foods in Japan as they have a high stability in autoxidation. Palm olefin, being in liquid form, is easy to use in frying, but it is inferior to palm oil in oxidative stability. The most important quality of frying oil, however, is stability after treatment under frying conditions and not that of fresh oil. In our previous paper1) we reported that saturated oils (palm and coconut) had much higher initial AOM values than unsaturated oils (soybean and safflower), but the AOM values decreased more sharply in saturated oils than in unsaturated oils after treatment under simulated deep-fat frying conditions. The ratio of tocopherol loss after the treatment was also larger in saturated oils than in unsaturated oils. In this study, the frying quality of palm oil and palm olein was compared under the same conditions as in the previous study1). The first test was done using a commercial palm oil and palm olein, and each of them was mixed with rice, rapeseed and corn oils, respectively. As a result, palm olefin showed a better stability in oxidation after the treatment. For confirmation, the second test was done on the oils which were prepared from the same lot of crude oil. The effect of antioxidants (SO and NMT) was also examined. A similar tendency was observed in the second test. 2 Experimentals 2 E1 Materials Commercial frying oils (palm oil, palm olein, rice, rapeseed and corn oils) were produced in April 1978, and their general properties are shown in Table-1. Silicone oil (SO): Shinetsu Silicone KF 96, 200cs, dimethylpolysiloxane. Natural mixed tocopherol (NMT): Eisai Co. Ltd., d-mixed Tocopherol Conc., purity; 82.5 %, ratio of isomers; ƒ 10.0%, ƒá 45.0%, ƒâ 45.0%. 2 E2 Preparation of RBD palm oil and palm olein A and B from the same lot of crude oil The crude palm oil was manufactured in Malaysia in March 1978 with the following general properties: acid value 7.5, iodine value 53.1, saponification value 197.2 and totox value 26.5. Palm oil is defined as a common product of crude palm oil. Palm olein A is fractionated 9
Table-1 General properties of commercial frying oils. Table-3 Fatty acid and glyceride compositions of prepared palm ail and palm olein. a Henick's method2). b Open-tubed melting point. from palm oil by surfactant and palm olein B is fractionated furthermore from palm olein A by solvent. Each oil was alkali refined, earth bleached and deodorized by the usual method to which was added 20ppm of citric acid. These procedures were carried out at the laboratory of Fuji Oil Co. Ltd. The general properties, fatty acid and glyceride compositions and the contents of Tocols are shown in Tables- 2, 3 and 4. The characteristic properties of the three types of oil are as follows. The iodine value of palm oil is 52.0 and palm olein A 53.2 and B 66.2. The melting point of palm oil is 34.5 Ž, palm olein A 20.3 Ž, and B below 10 Ž. The contents of trisaturated gly- a Programmed temperature GLC (OV 17, 2% Chromsorb Table-4 Tocols content in the crude and prepared palm oil and palm olein. cerides (GS3) showed the most remarkable difference among the various properties given in the tables. The content of GS3 in palm oil was 9.2%, while that in palm olein A and B was only 0.4 and 0.2%, respectively. The total Tocols content in decreasing order is palm Table-2 General properties of palm oil and palm olein prepared from the same lot of crude oil. olein B, A and palm oil, but the order for AOM value is reversed, being palm oil, palm olein A and B. 2 E3 Procedure of Tocols analysis Tocols were determined by the TLC-GLC method3) slightly modified by us. An aliquot of unsaponifiable matter equivalent to approx. 1mg of Tocols was subjected to TLC. Tocols were scrapped and extracted with ether after adding squalene (0.2mg) as an internal stan- 10
mixture of 0.5ml of hexamethyldisilazanetrimethyl chlorosilane-anhydrous pyridine (9:6 were trimethyl-silanized for 15min. The resulting TMS-sample was subjected to GLC. The conditions of GLC were as follows: apparatus, Shimazu GC-5A gas chromatograph equipped with a flame ionization detector (FID); column, 1.5% OV-17 Shimalite W 80 `100mesh; and column temperature, 240 Ž. The GLC data are shown in Table-5. Table-5 GLC data of tocols. 3 Results and Discussion 3 E1 Test on commercial oils Table-6 shows the analyzed data of commercial palm oil and palm olein treated under SDFC. The most remarkable difference between palm oil and palm olein is the changes of their oxidative stability measured by AOM value. The AOM value of palm oil decreased from 62.5 to 26.4 after the treatment, while that of palm olein from 47.0 to 38.9. Thus the AOM value after the treatment under SDFC became larger in palm olein than in palm oil. Similar results were obtained from oils which were mixed with liquid vegetable frying oils. Palm olein is considered to be a suitable oil in improving the oxidative stability of liquid vegetable frying oils such as rice, rapeseed and corn a Used for correcting areas for response variations and analytical losses 2 E4 Apparatus and method of simulation of deep-fat frying (SDFC) Fig.-1 shows the experimental apparatus which consists of the continuous water-spraying and heating system and is slightly modified from that used in the previous study1). Sixty grams of water is delivered to a sprayer by a perista mini pump3) at a con stant rate, and the water is sprayed under pressure from an air pump7). Other conditions are similar to those of the previous study. The main factors which affect the rate of fat deterioration are as follows: specific surface area exposed to air, 0.159cm2/g; rate of water vaporization, 15g/100g oil/h; and oil temperature, 180 }2 Ž. oils. 3 E2 Test on palm oil and palm olein prepared from the same lot of crude oil Table-7 shows the analyzed data of three types of palm oils which were prepared from the same lot of crude oil and treated under SDFC. It also shows that palm olein has a better stability in oxidation after treatment under SDFC than palm oil. Frying quality implies the stability against various deteriorations in deep-fat frying, and these qualities were evaluated by acid, peroxide and carbonyl values, viscosity increase, color and AOM value. Acid value is mainly related to hydrolytic deterioration. Peroxide and carbonyl values and viscosity increase are related to oxidation and/or thermal deterioration. We consider that carbonyl value is most suitable in comparing the degree of thermo-oxidative deterioration for the following reasons. When the oils which have a different fatty acid composition are thermo-oxidized under the same conditions, carbonyl value provides relatively approximate values to all oils, and also the method of determination is simple and reproducible. Thermo-oxidative deterioration causes not only 1. Stainless steel beaker; 2. Hot swirler; 3. Perista mini pump; 4. Sprayer; 5. Bolt slider, 6. Temperature regulator; 7. Air pump magnet type; 8. Needle valve; 9. Graduated cylinder for water supply; 10. Pressure adjuster; 11. Air cleaneṛ Fig.-1 Apparatus for the simulation of deep-fat frying. deterioration of glyceride but also destruction of Tocols in it, following the decrease of oxidative stability. The initial RBD palm oil has a high AOM value, because it contains Tocols sufficient in 11
Table-6 Analytical data of commercial palm oil and palm olein treated under SDFC and the effect of mixing with liquid vegetable frying oils. a Mixing ratio is fifty to fifty. b Figures in parentheses show the values before treatment. Table-7 Analytical data of prepared palm oil and palm olein treated under SDFC and the effect of antioxidants. a Figures in parentheses show the remaining ratio (%) b Figures in parentheses show the values before treatment amount for the unsaturation of its fatty acid compositions, although its Tocols content is lower than those of RBD palm olein A and B. Since palm oil loses much Tocols during the treatment, the amount of Tocols becomes insufficient to its fatty acid compositions, which causes the drop of AOM value. On the other hand, as palm olein A and B lose less Tocols than palm oil during the treatment, the AOM value is maintained at a high level, although the value is initially low due to the high unsaturation of fatty acid compositions. The difference between palm olein A and B is shown in AOM values before and after treatment. Palm olefin B shows a lower value than A due to the high degree of unsaturation. As reported previously, palm oil loses more Tocols than palm olefin A and B during the treatment probably because of the difference in the degree of unsaturation. The addition of SO is very effective in preventing hydrolytic and thermo-oxidative deterioration in the treatment, as is evident in comparing the data of acid, peroxide and carbonyl 12
values and viscosity increase. The addition of SO is also effective in decreasing the loss of Tocols during the treatment, following the drop of AOM value after the treatment, although it is not effective in improving the initial AOM value. On the other hand, the effect of NMT is less than SO on the hydrolytic and thermooxidative deterioration in the treatment, although it is considerably effective in improving the AOM values before and after treatment. The content of Tocols in RBD palm oil and References 1) E. Yuki and Y. Ishikawa, J. Am. Oil Chem. Soc., 53, 673 (1976) 2) A.S. Henick, M.F. Benca, and J.H. Mitchell, J. Am. Oil Chem. Soc., 31, 88 (1954) 3) P.W. Meijboom and G.A. Jongenotter, J. Am. Oil Chem. Soc., 56, 33 (1979) 4) T. Takagi and Y. Itabashi, Lipids, 12, 1062 (1977) 5) D. Chobanov, R. Tarandjiska and R. Chovanova, J. Am. Oil Chem. Sac., 53, 48 (1976) palm olein is somewhat deficient compared with other liquid vegetable frying oils such as soybean, rapeseed and rice, because Tocols in palm oils have a tendency to be lost in the refining process (Table-4). This may be due to the fact that tocotrienols are main components of palm oils. Moreover, palm oils contain little ć and ĉ tocopherols which play an important role as antioxidant property. Thus we think the addition of NMT which contains ć and ĉ tocopherols as the main component is very useful for RBD palm oil and palm olein. Frying qualities of commercial palm oil and palm olefin (Table-6) were almost the same as those of prepared palm oil and palm olein which were stabilized by the addition of 2.5ppm SO and 0.02% NMT (Table-7). Acknowledgment The authers are indebted to Fuji Oil Co. Ltd. for supplying us palm oils and for determining their properties. (Received Nov. 1983) 13