Tripalmitin and Monoacylglycerols As Modifiers in the Crystallisation Of
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Food Chemistry 122 (2010) 1185–1192 Contents lists available at ScienceDirect Food Chemistry journal homepage: www.elsevier.com/locate/foodchem Tripalmitin and monoacylglycerols as modifiers in the crystallisation of palm oil Rodrigo Corrêa Basso a,*, Ana Paula Badan Ribeiro a, Monise Helen Masuchi a, Luiz Antonio Gioielli b, Lireny A. Guaraldo Gonçalves a, Adenilson Oliveira dos Santos c, Lisandro Pavie Cardoso d, Renato Grimaldi a a Food Technology Department, School of Food Engineering, University of Campinas – UNICAMP, C.P. 6091, 13083-970 Campinas, SP, Brazil b Department of Biochemical and Pharmaceutical Technology, School of Pharmaceutical Sciences, University of São Paulo – USP, 05508-900 São Paulo, SP, Brazil c Social Sciences, Health and Technology Center, University of Maranhão – UFMA, 65900-410 Imperatriz, MA, Brazil d Institute of Physics Gleb Wataghin, University of Campinas – UNICAMP, C.P. 6165, 13083-970 Campinas, SP, Brazil article info abstract Article history: An exhaustive analysis of the crystallisation behaviour of palm oil was performed using low-resolution Received 10 September 2009 magnetic pulsed nuclear resonance, differential scanning calorimetry, polarised light microscopy and Received in revised form 2 February 2010 X-ray diffraction. The aim of this study was to characterise the changes induced in the crystallisation Accepted 29 March 2010 of palm oil by the addition of two different levels of tripalmitin and two different types of monoacylgly- cerols. The addition of monoacylglycerols led to the formation of a large number of crystallisation nuclei without changing the final solids content, accelerating the process of crystal formation, leading to the for- Keywords: mation of smaller crystals than those found in the refined palm oil. Higher levels of tripalmitin produced Palm oil crystallisation crystals with larger dimensions, reducing the induction period and resulted in a higher level of solids at Crystallisation modifiers Fat microstructure the end of the crystallisation period. The addition of monoacylglycerols and tripalmitin induced the for- Thermal behaviour mation of a polymorphic b-form. Crystalline morphology Ó 2010 Elsevier Ltd. All rights reserved. Fat polymorphism 1. Introduction talline network. A fat crystal network is formed by their aggrega- tion, due to the attraction exerted by Van der Waal’s forces. This The fatty acid composition of palm oil is characteristic and un- union continues to grow until a three-dimensional network is ique, containing approximately the same amounts of saturated and formed. The crystals start to join up in the presence of small al- unsaturated fatty acids, particularly palmitic and oleic acids. An- ready-formed structures, until they become crystal structures of other relevant factor is the significant amount of saturated fatty great volume, while the processes of nucleation and growth con- acids (10–16%) located in the sn-2 position of the triacylglycerols, tinue. A consequence of the simultaneous processes of crystallisa- these being determinant with respect to the crystallisation proper- tion and aggregation is that even with low proportions of ties. The triacylglycerols present are composed of 4.0–10.5% of tri- crystallised fat, a continuous network is formed. This process leads saturated, 41–59% of disaturated–monounsaturated, 32–54% of to the formation of solid bridges between crystals (sintering) and monosaturated–diunsaturated and 3.0–12% of triunsaturated aggregated particles. The number, size and shape of the particles (O’Brien, 2004). and the dimensions of the clusters will define the microstructure, The types of nucleation involved in fat crystallisation are di- which will determine the mechanical properties of the fat (Bois- vided into primary and secondary nucleation, the first being subdi- telle, 1988; De Graef, Dewettink, Verbeken, & Foubert, 2006; Fou- vided into homogeneous and heterogeneous. Primary nucleation bert, Dewettinck, Van de Walk, Dijkstra, & Quinn, 2007). occurs not only at the beginning of the crystallisation process, In a crystallisation process, the induction time may be defined but also parallel to secondary nucleation, being controlled by a suf- as the time required to detect the formation of the first nucleus ficient amount of thermodynamic forces, such as subcooling or in a subcooled or supersaturated system. This period includes the supersaturation. Most natural fats have sufficient amounts of actual time required for the nucleation, plus the time required to minority lipids to influence this process. The secondary nucleation detect crystallisation using an experimental technique. Since sub- process is linked to crystal growth from the surface of previously cooling is the temperature to which the triacylglycerol is cooled formed structures, or parts of these, which may give rise to a crys- below the equilibrium temperature and leads to an increased nucleation rate and shorter nucleation time (Metin & Hartel, 2005), one may consider that the induction time usually increases * Corresponding author. Address: Cidade Universitária Zeferino Vaz, Caixa Postal with an increase in crystallisation temperature and decrease in 6121, CEP 13083-862 Campinas, SP, Brazil. Tel./fax: +55 19 32891186. E-mail address: [email protected] (R.C. Basso). sample melting point. 0308-8146/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodchem.2010.03.113 1186 R.C. Basso et al. / Food Chemistry 122 (2010) 1185–1192 Monoacylglycerols assume an important role in the crystallisa- Following the above procedure, 1.01% (m/m) of MP or MBe was tion process. In some cases, when they are present at high levels or added, resulting in PoMp and PoMBe samples, respectively, each low temperatures, they generally contribute to the crystallisation one with 1.0% of monoacylglycerols regarding the final mass. process by increasing both the number of crystals and the nucle- ation rate. On the other hand, when they are present at low levels 2.3. Analytical methodology or higher temperatures, they will slow the crystallisation process down in a lipid material (Foubert, Vanhoutee, & Dewettinck, 2004). 2.3.1. Triacylglycerol composition Triacylglycerols levels in binary mixtures affect their crystallisa- Triacylglycerol composition was measured based on AOCS CE 5- tion behaviour. Both the thermal behaviour observed by DSC and 86 (2004) methodology, determined by an Agilent capillary gas the polymorphism value by X-ray diffraction have changed for dif- chromatography system, Series 6850, with flame ionisation detec- ferent fractions of tripalmitin blended with 1,3-dipalmitoyl-2- tor (FID), and an Agilent DB-17 capillary column (50% phenyl- oleoyl-glycerol (POP) and 1,2-dioleoyl-3-palmitoyl-glycerol (POO) methylpolysiloxane; length 15 m, internal diameter 0.25 mm and (Mihara, Ishiguro, Fukano, Taniuchi, & Ogino, 2007). 0.15 lm film thickness). Flow rate was 1.0 ml/min, linear velocity The lipid composition and crystallisation conditions influence of 40 cm/s, with a detector temperature of 375 °C, injector temper- the crystal format, and different polymorphic forms and crystal ature of 360 °C, oven temperature from 250 to 350 °C(5°C/min), morphologies are possible. The crystals are aggregated into larger followed by 350 °C for 20 min, carrier gas of helium; injected vol- structures forming a network, which characterises the fat micro- ume of 1.0 ll with 1:100 split. Retention times were determined structural level. The type of polymorph characteristic of a fat or comparing with commercials standards, samples and others vege- oil is dependent on the distribution of fatty acids in the triacylglyc- table oils (palm oil, soybean oil, and palm kernel oil) previously erol molecule, and the degree of randomisation is particularly indentified and quantified in our laboratory. All fractions of triacyl- important. In turn the microstructure concept includes informa- glycerols in palm oil were quantified based on relative peak area, in tion about the state, quantity, shape, size, spatial relationship duplicate. The results were compared with those obtained follow- and interaction amongst all the components of the crystalline net- ing the procedure of Antoniosi Filho, Mendes, and Lanças (1995) work, and has an enormous influence on the macroscopic proper- and with a literature compilation (Andrikopoulos, 2002). ties of the fats (Marangoni & Hartel, 1998; Ribeiro et al., 2009; Shi, Liang, & Hartel, 2005). 2.3.2. Fatty acid composition of the monoacylglycerols Although there are explanations about the mechanisms that Fatty acid composition was determined in duplicate by an Agi- determine the crystal type formed, there is little information about lent capillary gas chromatography system, Series 6850, FID detec- the way the presence of some compounds modifies crystal poly- tor, with an Agilent DB-23 capillary column (50% cyanopropyl- morphism. Knowledge of this effect could make it possible to con- methylpolysiloxane; length 60 m, internal diameter 0.25 mm and trol palm oil crystallisation, leading to its application in a huge 0.2 lm film thickness). Flow rate was 1.0 ml/min, linear velocity variety of products and processes. The objective of this study was of 24 cm/s, with a detector temperature of 280 °C, injector temper- to make a complete characterisation of the changes caused in the ature of 250 °C, oven temperature: 110 °C for 5 min, 110–215 °C crystallisation behaviour of refined palm oil by the addition of (5 °C/min), 215 °C for 34 min, helium carrier