Food Sci Techno/. Int. Tokyo, 3 (1), 77-81, 1997
Polymorphic Behavior of Palm Oil and Modified Palm Oils
Hidetoshi ISHIKAWA, Makoto SHIOTA,Mototake MURAKAMIand lchiro NAKAJIMA
Technology and Research Institute, Snow Brand Milk Products Co., Ltd., /-1-2, Minamida~ Kawagoe, Saitama 350-1], Ja pa n
Received September lO, 1996
Refined, bleached and deodorized palm oil, its purified palm triacylglycerol (PTG), palm olein (PO), palm stearin (PS) and high melting palm stearin (HMPS) fractions as well as randomized palm oil (RP) and its high melting randomized palm stearin (HMRPS) fractions were solidified at 5'C and kept isothermally at 10, 20 and 30"C for 60 days. X-ray diffraction showed that PTG was in P' form crystals, while palm oil and RP were in both a and ~' forms at 5'C. In HMPS and HMRPS, the higher percentage of ~-transformation was observed with a higher content of trisaturated triacylglycerols and at a higher temperature. RP transformed from P' to the intermediate form crystals during prolonged storage. Other fats were stable in P' form crystals. Palm oil, RP, HMPS and HMRPS exhibited long-spacing values between those of tripalmitin and tristearin in a, P' and ~ modifications, respectively. This confirms that palm oil and its modified oils form a double-chain-length conformation.
Ke ywords: fractionation, interesterification, olein, palm oil, polymorphic transformation, stearin
Palm oil is a vegetable oil that has been widely used in the Materials and Methods manufacture of products such as margarines, shortenings, Refined, bleached and deodorized palm oil, and its palm cooking olls and confectlonery fats (Kheiri, 1985; Murase, olein (PO) and palm stearin (PS) fractions were obtained 1986; D'Souza et al, 1991; Ohfuji & Fujiwara, 1994). The use from The Nisshin Oil Mills, Ltd. (Tokyo). The purified palm of palm oll in foods, however, has been limlted by its physical triacylglycerol (PTG) fraction was separated from palm oil by properties, namely, the presence of granular crystals ( Ishikawa thin-layer chromatography. The high melting palm stearin et a/, 1980; Watanabe et al., 1992) and its low rate of (HMPS) fraction was obtained by solvent-recrystallization as crystallization (van Putte & Bakker, 1987; Ng, 1990). In follows: PS was dissolved In acetone at the ratio of I : 5 (w : margarines and shortenings, solid fats should consist of ~' v). The solution was left overnight in a water bath at 20'C to form crystals, which confer a smooth texture to the products. allow crystallization. The liquid fraction was then removed On the other hand, the p form crystals confer a rough texture by filtration. The solvent was removed from the crystals under to the products. The crystal forms depend on the triacylglycer- vacuum. ol composition of blended oils and the rate of crystallization. Random interesterification of palm oil was carried out at Interesterification has been adopted to change the triacyl- 80'C in an I / vessel. Sodium methoxide was used at a level glycerol composition. Random interesterification involves of 0.3% by weight of the oil. High melting randomized palm rearrangement of fatty acids within and between triacylglyc- stearin (HMRPS I O, HMRPS20) fractions were obtained from erols. Rearrangement of acyl residues in triacylglycerols randomized palm oil (RP) by solvent-crystallization (at lO results in oils with new physical properties and different and 20'C, respectively, in acetone). For comparison of poly- polymorphic behavior. Today, interesterification is used as morphic behavior, tripalmitin and tristearin (Sigma Chemi- frequently as fractionation in various areas. The interesterifi- cal Co., St. Louis, MO) were used as standard trisaturated cation of triacylglycerols has been extensively reviewed triacylglycerols. (Husted, 1976; Matsui, 1979; Laning, 1985; Mori, 1989). The fatty acid compositions were determined by D'Souza et al. ( 1992) studied the polymorphic behavior of transesterification and analysis of methyl esters in a Hewlett- solid fats found In commercially available soft margarines Packard gas chrornatograph (Model 5890, Wilmington, DE) and suggested that solid fats can be provided by interesterified equipped with a flame ionization detector. Separations of the palm oil products. Duns ( 1 985) studied the properties of palm methyl esters were performed on a SP-2380 fused-sllica oil before and after interesterification and concluded that the capillary column (30 mX0.32 mm i.d.; Supelco, Inc., Bel- application of interesterification techniques, although useful, lefonte, PA). The temperatures were 250'C for injection, was restricted. However, Iittle is known about fundamental 260'C for the detector, and 170'C for the column. research on the polymorphic behavior of modified palm oils. The diacylglycerol content in palm oil and PTG was In this study, we have dealt with modified palm oils formed measured with a TLC/FID Iatroscan TH- 1000 (Iatron Labo., by random interesterification and solvent-fractionation and Inc., Tokyo). investigated the effect of the triacylglycerol composition of The iodine value was determined according to the Wijs these oils on their polymorphic behavior when placed at a method, AOCS official method Cd 1-25. constant temperature for a given period. The solid fat content (SFC) was measured by pulsed nuclear magnetic resonance (pNMR) in an NMR analyzer 78 H. IsHIKAWA et al.
(Model SFC-900, Praxis Corp., San Antonio, TX) according to 5'C showed a mixture of c! and ~' form crystals, then to AOCS ofncial method Cd 16-81. maintained the ~' form crystals at I O and 20'C. PTG was in Triacylglycerol compositions were determined by HPLC. ~' form crystals at 5, 10 and 20'C. The crystal form observed The apparatus for HPLC was a Waters LC Module l at 5'C depended on the diacylglycerol content of palm oil and equipped with a Waters differential refractometer (Model PTG ( I .7% and 0.0%, respectively). Persmark et al showed 410). Separation was performed on a Nova-Pak C18 column that the lifetime of c! form crystals is considerably increased (300 mmx3.9 mm i.d.; Waters, Millipore Corp., Milford, by the presence of partial acylglycerols (Berger, 1975; Pers- MA). The moblle phase was a mixture of acetone/acetonitrile mark et a/, 1976). (50 : 50), and the flow rate was I ml/min at 45'C. Peak X-ray diffraction lines over d=8 A (CuKcY:26
Table 1. Fatty acid composition (%) and iodine value of palm oil and its fractions. Fatty acid Palm PTG") pOb) PSc) HMPSd) RPe) HMRPSIOj) HMRPS20") i2 : O 0.2 0.2 l ,4 O. l 0.2 O. l O, l 14 : O l .2 l.l l ,6 1 .5 I .9 l.l l .O I .O 16 : O 45.9 45.4 40, 1 47.6 73. I 43.6 60.0 72,5 16: l O.4 O.3 0,3 0.3 0.2 0,2 18 : O 4.4 4.6 5,0 I0.5 8.4 4.8 6. l 6.7 18 : l 37.8 38.3 41,7 32,6 13.3 39.5 24.8 l 5.4 18 : 2 9.4 9.5 9.6 7.3 2.8 9.8 6.0 3,4 20 : O 0.7 0.6 O.3 0.4 0.5 0.7 l .2 O,5
lodine value 53.0 53. l 56,0 45, i l 4.4 53.4 35.3 22.5 ~) Purified palTn triacylglycerol fraction, b) palm olein, o palm stearin, d) high melting palm stearin (20'C, acetone), e) randomlzed palm oil j) hrgh melting randomized palm stearin ( lO'C, acetone), g) high melting randomized palm stearin (20'C, acetone).
Table 2. Solld fat content (%) of palm oil and rts fractrons Palm PTG") pO b) PSc) HMPSd) RPe) HMRPS I O~ HMRPS20~ l O'C 5 1 .7 66.6 34.5 60.4 OO 47.9 IOO OO 20'C 20. 1 24.4 6.0 34.3 OO 30.0 74.4 OO 30'C l I .O l 1.9 1.5 25.3 OO l 8.8 66.2 OO *) Purified palm triacylglycerol fraction, b) palm olein, c) palm stearin d) high melting palm stearin (20'C, acetone), ') randomized palm oil, j) high melting randomized palm stearin ( IO'C, acetone), g) high melting randomized palm stearin (20'C, acetone). Polymorphic Behavior of Palm Oil and Modified Palm Oils 79
Table 3. Short and long spacings (A) of palm oil and its fractions at different temperatures. Condition Fat Short spacings Long spacings~b) Form 5'C, I h Palm 4.35(S) 4.23(w) 3.90(w) 47.2(s) 43.3(w) 15.9(w) I 4.4(w) *>~' PTG') 4.35(S) 4.23(s) 3.90(m) 43.3(S) p' pO d ) 4.35(S) 4.23(m) 3.90(m) 43.5(W) cY<< ~' HMPS') 4. 1 5(s) 46.0(s) 15.5(s) l 4. I (w) R P j) 4.35(S) 4.23(s) 3.90(m) 47.2(m) 43.3(m) l 5.9(w) 14.5(m) c!+fi' HMRPS I Og) 4.62(w) 4.39(s) 4.27(s) 3.90(s) 43.9(s) ~'>> ~ HMRPS20") 4.62(S) 4.35(S) 4.27(s) 3.90(s) 43.7(s) p'>fi Tripalmitin 4. 1 5(s) 46.0(s) l 5.3(m) lO'C, 60 days Palm 4.37(s) 4.23(s) 3.90(s) 43.3(s) 14,4(m) fi' PTG 4.37(s) 4.23(s) 3.90(s) 43.3(s) 14,4(m) fi' PO 4'37(S) 4.23(S) 3.90(s) 43.3(m) 14,4(m) fi' HMPS 4.60(s) 3.90(s) 3.77(m) 42.0(s) l 4, I (m) fi RP 4.62(s) 4.37(s) 4.23(s) 3.90(s) 43.3(s) l 4. 5(m) ~'>~ HMRPSIO 4.62(s) 4.37(s) 4.27(s) 3.88(s) 43.3(s) l 4.3(m) ~'< p HMRPS20 4.62(s) 4.37(m) 4.23(m) 3.88(s) 42.4(s) 14.2(m) ~' T able 4. Triacylglycerol composrtron (%) of palm oil and rts fractrons as determmed by HPLC Trlacylglycerol Palm pOa) HMPSb) RPc) HMRPSIOd) HMRPS20') PPP 6.8 0.8 59.8 9*3 31,l 47.0 PPS l .5 1 1 .4 2.6 8.4 12.7 POP+PPO 31.5 32.8 17.2 24.7 25.0 19.2 POs 5.7 5.6 2. l 4.6 4,6 2.9 PO0+0PO 21.5 24. 1 0.8 2 1 .O 8,5 4.2 PL0+POL 9.5 l 1.2 l I .3 4,5 2.0 SOO 2.6 2.8 2.3 ppL+PLP+MOP l0.4 l 1.7 3.0 8. I 6.0 4.0 OOO 3.4 3.8 5.4 2.0 OO L l.5 l .8 4.3 l .7 ~) Palm olein, b) high melting palm stearin (20'C, acetone) c) randomized palm oil, d) high melting randomized palm stearin ( lO'C, acetone), ') high melting randomized palm stearin (20'C, acetone). glycerol. polymorph among the samples analyzed, and tristearin Randomizled palm oi/ and fractions RP showed a showed the longest ones. Palm oil, RP and other fractions mixture of a and p' form crystals at 5'C, Iike palm oil. On the exhibited intermediate values between tripalmitin and tri- other hand, it exhibited a weak line at 4.6 A after I day at lO stearin. This confirms that palm oil and RP form double- or 20'C. During the period at 10 or 20'C, there was a chain-length conformation, because they had the same long transformation to p form crystals. The crystals, however, did spacings in the a and p' modifications. not show a perfect ~ form but an intermediate form. As for Relation between triacylglycerol composition and fi- the long spacings of RP, the length of the c-axis in the unit cell transformation We investigated the relation between the was the same as that of palm oil in ~' form crystals. In case percentage of p form crystals and the content of trisaturated of HMRPS (IV 35, 23), the X-ray diffraction data indicated triacylglycerols in higher melting stearins and tripalmitin that they had transformed from ~' to ~ form crystals. stored at various temperatures for different periods of time Especially, the higher melting fraction HMRPS20 changed to (Figs. l, 2). High melting stearin fractions easily transformed ~ form crystals in a short time. from ~' to p form crystals as the trisaturated triacylglycerol Chain-packing in each modlfuation The long and content and storage temperature increased. However, the short spacings in each modification are summarized in Table development of ~ foam crystals in HMPS was low when 5. Tripalmitin showed the shortest long spacing for each stored at lO'C for I day. On the other hand, tripalmitin was 80 H. IsHIKAWA et al. Table 5. Characteristic long and short spacings (A) ofvarious fat samples. 1 OO 30~C Pol ymorph F at Short spacings Long spacings c! Tripalmitin 4 15 46 O 15.3 ,( HMPS") 4 15 46 O 15.5 / /L* Palm 4 20 47 2 1 5.9 80 / l}t R Pb) 4 20 47 2 l 5.9 20~c / Tristearin 4 15 50 6 \j / fi Tripalmitin 4 20 3.80 42 6 '~ I ~~ . 4 37 4 23 3.90 43 3 \, 60 Palm 44 ~ ll \ // Io~c t 4 37 4 23 3.90 43 3 44 , RP ,1~O Tristearin 1" I 4 20 3.80 47 2 (:a I 3.7 / ~ Tripalmitin 4.60 3 86 3.70 40 6 ~ / V c$ 4.60 3 90 3.74 41 3 l 3.8 4J 40 r~ HMPS El 1 4.0 t H M R PS20") 4.62 3 90 3.77 42 O I La) HMRPSIOd) 4.6,~ 3 92 3.80 42 2 l 4. 1 ~ I Tri s teari n 4.60 3 86 3.70 44 6 \ ! ~) High melting palm stearin (20'C, acetone), b) randomized palm oil, ') high 20 melting randomized palm stearin (20'C. acetonc), d) high melting randomized tt palm stearin ( 10'C, acetone). o 60 1 OO O 20 40PPP+PPS(%) 80 100 Fig. 2. Relation between the perccntage offi form crystals and the trisaturat- 30~c ed triacylglycerol content (60 days after solidification). 1~~ palm oil, A high melting palm stearin, e randomized palm oil, I high melting randomized palm 80 stearln (lO'C, acetone), A high melting randomized palm stearin (20'C, acctone), ' tripalmltin. f* ~~ 2 o ~c/A/A\ 60 ~ glycerol content. We assumed that diunsaturated and tri- o ~ unsaturated acylglycerols in RP accelerated the transforma- G~ / / /\\ '~ \ \ ~ tion at 20'C by behaving as a solvent, thus causing the cE' 40 tJ c~ migration of molecular chains in the lattice. e, ll ~ \A When the content of monoacid trisaturated triacylglycerols 1' // ro~c cL / such as trlpalmitin was extremely high, the percentage of fl 20 \\ transformation from a! to ~ form crystals under 30'C was \h lower than that of other stearin fractions. \ The results obtained from this study indicated that the ~-transformatlon of modified palm oils can be affected by the O O 20 40 60 8 O I OO trisaturated trlacylglycerol content and storage temperature. PPP+PPS(%) However, the physical characteristics and polymorphic Fig. 1. Relation between the percentage of ~ form crystals and the trisaturat- behavior of these oils when incorporated into a margarine ed triacylglyceroi content ( I day after solidification). ". palm oil, A high melting formula would be considerably influenced by other factors paim stearin, e randomized palm oil, I hlgh meiting randomized palm stearin such as the triacylgycerol composition of blended oils, the ( lO'C, acetone), L high melting randomized palm stearin (20'C, acetone), * presence and klnd of emulsifiers, and the processing condi- tripalmitin. tions. In c! form crystals when stored at 10 or 20'C but transformed References to p form crystals when stored at 30'C for 60 days. Berger, K.G. ( 1 975). Uses of palm oil in the food industry. Chem. Ind., Data on triacylgycerol composition, polymorphic transfor- 1, 9 l0-9 1 3. Chapman, D. (1962). The polymorphism of glycerides. Chem. Rev., mation, and the length of long spacings in ~ forrn crystals can 62, 433-456. be summarized as follows. High melting stearin fractions Defense. E. ( 1984). Application de la chromatographie liquide haute transformed into p form crystals in proportion to the trlsatu- performance a 1'analyse des triglycerides des graisses vegetales et rated triacylglycerol content. The length of long spacings in ~ animales et de leurs fractions obtenues par cristallisation fraction- nee. Rev. Franc. Corps Gras, 31, 123-129. form crystals approached that of tripalmitin as the trisaturated Defense, E. (1985). Fractionation ofpalm oil. J. Am. Oi/ Chem. Soc., triacylglycerol content increased. Lower fractionation temper- 62, 376-385. ature yielded more middle meltlng triacylglycerols in D'Souza, V., deMan, J.M, and deMan, L. (1991). Chemical and fractionated solid fats: POP, PPO, POS. Hence the long physical properties of the high melting glyceride fractions of spacings of origlnal fats were longer than those of high commercial margarines. J. Am. Oil Chem. Soc., 68, 153-162. D'Souza, V., deMan, J.M, and deMan. L. (1992). Chemical and melting stearin fractions. On the other hand, RP transformed physical properties of the solid fats in commercial soft margarines. from ~' to ~ form crystals faster than HMRPS 10 when stored J. Am. Oil Chem. Soc., 69, I 198l205. at 20'C for 60 days in spite of its lower trisaturated triacyl- Duns, L.M. ( 1985). Palm oil in margarines and shortenings. J. Am. Oil Polymorphic Behavior of Palm Oil and Modified Palm Oils 81 Chem. Soc., 62, 408-410. Ng, W.L. ( 1990). A study of the kinetics of nucleation in a palm oil Husted, H.H. (1976). Interesterification of edible oils. J. Am. Oil melt. J. Am. Oil Chem. Soc., 67, 879-882. Chem. Soc., 53, 390-392. Ohfuji, T. and Fujiwara, K. ( 1994). Production and use of palm oil. In Ishikawa, H., Mizuguchi, T. and Kondo, S. ( 1 980). Studies on granular "Nutritional and Health Aspects of Palm Oil," ed. by K. Aibara. crystals growing in palm oil. J. Jpn. Oil Chem. Soc., 29, 235-242. International Life Sciences Institute of Japan, Tokyo, pp. 32-60. Jacobsberg, B. and Oh Chuan Ho ( 1 976). Studies in palm oil crystalli- Persmark, U.. Melln. K.A. and Stahl. P.O. (1976). Palm oil, its zation. J. Am. Oi/ Chem. Soc., 53, 609-617. polymorphism and solidification properties. Rev. Ita!. Sostanze Kheiri. A.S.M. (1985). Palm oil products in cooking fats. J. Am. Oil Grasse, 53, 301 -308. Chem. Soc., 62, 410-416. Sato, K., Arishima, T., Way, Z.H., Ojima, K., Sagi, N. and Mori, H. Laning, S.J. ( 1985). Chemical interesterificatlon of palm, palm kernel ( 1989). Polymorphism of POP and SOS. J. Am. Oil Chem. Soc., 66, and coconut oils. J. Jpn. Oil Chem. Soc., 62, 400-405. 664-679. Matsui, N. ( 1979), Interesterification and its application to food fat van Putte, K.P.A.M. and Bakker, B.H. ( 1987). Crystallization kinetics Industries. J. Jpn. Oi! Chem. Soc., 28, 680-688. of palm oil. J. Am. Oil Chem. Soc., 64, I 138-1 143. Mori. H. (1989). Solidification problems in preparation of fats. In Watanabe, A., Tashima, I., Matsuzaki, N., Kurashige, J. and Sato, K. "Crystallization and Polymorphism of Fats and Fatty Acids," ed. ( 1992). On the formation of granular crystals in fat blends contain- by N. Garti and K. Sato. Marcel Dekker, Inc., New York, pp. 423- ing palm oil. J. Am. Oil Chem. Soc., 69, 1077-l080. 442 . Yap. P.H., deMan, J.M, and deMan, L. ( 1989). Polymorphism of palm Murase. Y. (1986). Current situation of palm oil production and oil and palm oil products. J. Am. Oi! Chem. Soc., 66, 693-697. utilization. J. Jpn. Soc. Food Sci. Technol., 33, 291-299.