Hard fats as additives in palm oil and its relationships to crystallization process and polymorphism

LWT - Food Science and Technology xxx (2015) 1e8

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Hard fats as additives in palm oil and its relationships to crystallization process and polymorphism Glazieli Marangoni de Oliveira a, *, Ana Paula Badan Ribeiro b, Adenilson Oliveira dos Santos c, Lisandro Pavie Cardoso d, Theo Guenter Kieckbusch a a

School of Chemical Engineering, University of Campinas e UNICAMP, Campinas, Brazil School of Food Engineering, University of Campinas e UNICAMP, Campinas, Brazil ~o, Imperatriz, Brazil Social Sciences, Health and Technology Center, University of Maranha d Institute of Physics “Gleb Wataghin”, University of Campinas e UNICAMP, Campinas, Brazil b c

a r t i c l e i n f o

a b s t r a c t

Article history: Received 14 November 2014 Received in revised form 8 April 2015 Accepted 13 April 2015 Available online xxx

The application of palm oil in fat-based product can be inappropriate due to its low crystallization rates and formation of crystalline clusters in post-processing stages. The adjustment of these properties can be achieved with the addition of hard fats, which are low-cost industrial products resulting from the process of total catalytic hydrogenation of liquid oils. During the crystallization of palm oil, these components can act as preferential nuclei in a crystalline ordering process, and may induce or stabilize specific polymorphic habits. The present work evaluated the addition of hard fats from palm kernel (PKO), palm (PO), soybean (SO), cottonseed (CO) and crambe oils (CR), at concentrations of 1 g, 3 g, and 5 g/100 g of oil blend, on the crystallization behavior of palm oil. The study involves the crystallization kinetics, thermal behavior and polymorphism. The addition of hard fats provided a significant decrease of the induction time for nucleation in all blends, except with PKO. All blends showed a preference for crystallization in the polymorphic habit b0 , but blends with SO and CR, however, formed a miscellany of b0 þ b crystals. Adding hard fats to palm oil increase its compatibility for uses in formulations of cocoa butter alternatives and fat-based products. © 2015 Elsevier Ltd. All rights reserved.

Keywords: Palm oil Hard fats Crystallization Polymorphism Lipid structuring

1. Introduction Processed products such as margarines and shortenings, rich in palm oil may present slow crystallization rates and critical posthardening effects due to its glyceride composition, especially high content of partial glycerides (Sue & Pantzaris, 2009). Monoacylglycerols are present at concentrations below 1 g/100 g, but diacylglycerols (DAGs) are found at levels of 5e8 g/100 g and may influence the crystallization history, delaying the crystallization

List of abbreviations used: PKO, fully hydrogenated palm kernel oil; PO, fully hydrogenated palm oil; CO, fully hydrogenated cottonseed oil; SO, fully hydrogenated soybean oil; CR, fully hydrogenated crambe oil; TAG, triacylglycerol; SFC, solid fat content; DSC, differential scanning calorimetry; C12:0, La, lauric acid; C14:0, M, myristic acid; C16:0, P, palmitic acid; C18:0, S, stearic acid; C20:0, A, arachidic acid; C22:0, Be, behenic acid. * Corresponding author. School of Chemical Engineering, 500, Albert Einstein ria Zeferino Vaz, University of Campinas, UNICAMP, 13083Ave., Cidade Universita 852, Campinas, SP, Brazil. E-mail address: [email protected] (G.M. de Oliveira).

rate of industrial palm oil (Bergel, 2001; Oliveira, Grimaldi, & Gonçalves, 2014; Smith, 2001). Furthermore, the triacylglycerol (TAG) profile of palm oil is very heterogeneous, with different possible combinations of saturated and unsaturated fatty acids with distinct carboxylic chain length, favoring the development of complex isothermal crystallization profiles with polymorphic diversifications. Therefore, palm oil undergoes different polymorphic events during crystallization and the transition from the a Form Crystal to the b0 Crystal in palm oil is extremely slow compared to most other natural fats (Fredrick, Foubert, Sype, & Dewettinck, 2008). The polymorphism of lipid crystal and the crystallization processes affect the hardness, texture, rheology, and spreadability of lipid-based solid products (Sato, García, Calvet, Diarte, & Ueno, 2013). External factors, as thermal variation, shear, and additives, applicable in crystallization processes also influence the functionality of vegetable oils and the organization of the TAGs. A small disturbance in these properties will change the kinetics of polymorphic transformations and hence can affect the

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Please cite this article in press as: de Oliveira, G. M., et al., Hard fats as additives in palm oil and its relationships to crystallization process and polymorphism, LWT - Food Science and Technology (2015), http://dx.doi.org/10.1016/j.lwt.2015.04.036

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crystallization and melting behavior of oils and fats. As an alternative to improve and/or modify these attributes, it is possible to use crystallization promoters, such as hard fats, additives obtained by total catalytic hydrogenation of liquid oils. Hard fats present homogeneous saturated TAG composition, high melting point (>40  C) and can act as modifiers of the crystallization process. Furthermore, they can act as preferential nuclei in the crystal lattice ordering and induce specific polymorphic habits. Sato et al. (2013) reported that the relative rates and the extent of crystallization of a, b0 and b polymorphs are influenced by the rate of nucleation, which increases with the increase of supercooling and is governed by the activation free energy for nucleation, temperature, mass and heat transfer rates, and attachment/ detachment rates of lipid molecules between cluster and liquid. Arishima and McBrayer (2002) added crystallization accelerators or seeding agents to compounds products formulated with palm kernel stearin and observed an acceleration in the crystallization of chocolates, stability to fat bloom formation with easy demolding of the compound. Verstringe, Dewettinck, Ueno, and Sato (2014) showed that morphology of the palm oil crystals were oriented by crystallized monopalmitin additives and the palmitic acid present in both lipids phases played decisive roles in a template effect. Hard fats from palm oil, cottonseed oil, soybean oil and crambe oil were used with success to modulate the crystallization kinetics and thermal behavior of cocoa butter (Ribeiro, Basso, Santos, et al., 2013). This study uses DSC outputs, X-ray diffraction pattern and isothermal crystallization data in an attempt to understand the basic polymorphic transitions involved in the crystallization process of palm oil added with hard fat. 2. Materials and methods 2.1. Materials Deodorized palm oil was supplied by Agropalma S/A (Brazil). Five different hard fats, provided by Cargill Agrícola S/A (Itumbiara, Brazil), were evaluated in this study: hard fat of palm kernel oil (PKO) (45.5 g/100 g C12:0, 15.8 g/100 g, C14:0, 9.2 g/100 g C16:0, 23.0 g/100 g C18:0); hard fat of palm oil (PO) (36.2 g/100 g C16:0, 61.2 g/100 g C18:0), hard fat of cottonseed oil (CO) (23.2 g/100 g C16:0, 73.9 g/100 g C18:0), hard fat of soybean oil (SO) (10.5 g/ 100 g C16:0, 87.3 g/100 g C18:0), and hard fat of crambe oil (CR) (2.8 g/100 g C16:0, 31.6 g/100 g C18:0, 56.3 g/100 g C22:0) where C12:0, C14:0, C16:0, C18:0 and C22:0 correspond to lauric, myristic, palmitic, stearic and behenic acids, respectively. The TAG composition of the hard fats are: PKO (21.5 g/100 g LaLaLa, 15.4 g/ 100 g LaLaM, 9.3 g/100 g LaLaP, 8.67 g/100 g LaMP, 6.2 g/100 g LaSM, 6.2 g/100 g LaSP, 6.2 g/100 g LaSS), PO (35.0 g/100 g PPS/PSP, 38.8 g/100 g PSS, 19.2 g/100 g SSS), CO (19.8 g/100 g PPS/PSP, 45.6 g/100 g PSS, 32.4 g/100 g SSS), SO (29.8 g/100 g PSS, 63.8 g/ 100 g SSS), and CR (28.6 g/100 g SBeBe, 18.1 g/100 g BeBeBe, 17.2 g/ 100 g SSBe, 9.9 g/100 g PSBe, 9.5 g/100 g SABe), where La, M, P, S, A and Be correspond to lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid and behenic acid, respectively (Ribeiro, Basso, & Kieckbusch, 2013). 2.2. Preparation of the blends Initially, all raw materials were melted at 100  C. Then, three different proportions of each hard fat were added to palm oil: 1 g/ 100 g, 3 g/100 g and 5 g/100 g of blend, totalizing fifteen different blends. After the addition, all blends were stirred for 10 min to ensure complete homogenization and then stored in a refrigerator at 10  C until use.

2.3. Crystallization isotherm The samples were melted at 100  C for 15 min and kept in a high precision dry bath (TCON 2000, Duratech, Carmel, USA) at 70  C for complete destruction of their crystalline history. The increase in solid fat content due to static crystallization was monitored by a Nuclear Magnetic Resonance spectrometer (RMN) Bruker pc120 Minispec (Silberstreifen, Rheinstetten, Germany), with the reading compartment stabilized at 25  C. The data acquisition was automatic, with measurements taken every minute, during 90 min for the blends and 120 min for palm oil. The crystallization kinetics was parameterized by the induction time, tSFC e time relative to the onset of the formation of crystals e and by the maximum solid fat content, SFCmax. The constants of the Avrami model (Equation (1)), fitted to the data, were used to classify the nature of the crystal growth process and to quantify the crystallization kinetics: n SFC ¼ 1  eB*t SFCmax:

(1)

where, SFC corresponds to the solid fat content at a specific time, t, usually in minutes, SFCmax corresponds to the maximum value of SFC found during crystallization, n is the Avrami exponent (dimensionless) and indicates the mechanism of crystal growth, “B” is the Avrami constant (min-n) and represents the crystallization rate constant (Marangoni, 2005). The determinations were performed in duplicate. 2.4. Thermal behavior by differential scanning calorimetry (DSC) Thermal analyzes of the samples were performed by differential scanning calorimetry (DSC) according to American Oil Chemists' Society [AOCS] (2009) Cj 1-94 method. A TA Thermal Analyzer, model Q2000 V4.7A, coupled to a RCS90 Refrigerated Cooling System (TA Instruments, Waters LLC, New Castle, USA) was used. About 8e10 mg of the melted samples were weighed into aluminum pans, sealed and then thermally equilibrated. Another aluminum pan, empty and hermetically sealed, was used as a reference. The thermal analysis conditions were 5 min at a constant temperature of 80  C followed by cooling down to 40  C, at a rate of 10  C/min and maintenance at this temperature for 30 min. The TA Universal Analysis V4.7A software was used to obtain the curves and the following parameters: onset of the temperature of crystallization (Toc); peak temperature of crystallization (Tc); enthalpy of crystallization (DHc); and offset temperature of crystallization (Tof). All the DSC analyses were carried out in triplicate. 2.5. X-ray diffraction The polymorphic form of the fat crystals was determined by Xray diffraction, according to the AOCS Cj 2-95 method (AOCS, 2009). Analyses were performed on a Philips PW 1710 diffractometer (PANalytical, Almelo, the Netherlands), using Bragg-Brentano geometry (q:2q) with radiation Cu ka (l ¼ 1.54178 Å, voltage 40 kV and current of 30 mA). The measurements were obtained with steps of 0.02 in 2q and acquisition time of 2 s, with scans from 5 to 40 (range 2q). Before determinations, the samples were melted in a microwave oven at about 100  C and stabilized at 25  C for 24 h in an incubator. The identification of the polymorphic forms was determined from the characteristic short spacings of each crystal. The relative amounts of the different types of crystals were estimated by the relative intensity of the short spacings (Schenck & Peschar, 2004).

Please cite this article in press as: de Oliveira, G. M., et al., Hard fats as additives in palm oil and its relationships to crystallization process and polymorphism, LWT - Food Science and Technology (2015), http://dx.doi.org/10.1016/j.lwt.2015.04.036

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2.6. Statistical analysis Statistical analyzes were performed using the Statistical System version 9.1 software (SAS Institute Inc., USA). In order to determine significant differences between the mean values of the tests, an analysis of variance (ANOVA), followed by Tukey's test were applied. The confidence interval was 95%. 3. Results and discussion 3.1. Crystallization isotherms The complex crystallization behavior of palm oil can cause numerous practical problems in fat-based products and the crystallization isotherms are able to predict important information about this behavior. Fig. 1 shows the evolution of SFC as a function of time, at 25  C, for palm oil and for the evaluated blends.

Fig. 1. Isothermal crystallization at 25  C for palm oil (*)and palm oil added to hard fats of (A) PKO, fully hydrogenated palm kernel oil; (B) PO, fully hydrogenated palm oil; (C) CO, fully hydrogenated cottonseed oil; (D) SO, fully hydrogenated soybean oil; and (E) CR, fully hydrogenated crambe oil, at 1 g/100 g ( ), 3 g/100 g ( ) and 5 g/100 g (◊).

▵

▫

3

For the blends of palm oil with PKO, PO, CO and SO hard fats, typical sigmoidal-shaped curve were obtained. At the beginning, there was a near-baseline signal output corresponding to the induction period for stable nucleation, followed by a period of rapid crystallization (Herrera, Gatti, & Hartel, 1999). Hard fats induced dramatic changes in the crystallization behavior of palm oil, except for the PKO hard fat (Fig. 1A), where the experimental points for blends with PKO at 1 g/100 g and 3 g/100 g overlapped the values obtained for palm oil, and only a discreet difference was perceptible in blends with 5 g/100 g. The crystallization curves with CR suggest a different and more complex behavior. In these blends, the solidification process presented two plateaus, characterizing a bimodal type crystallization. First, there was a rapid solid fat increase after a short induction period, and then, in a second step of crystallization, the SFC curve describes the typical sigmoidal shape increase. Two hypotheses can be postulated to explain the formation of this intermediate level in the blends with CR. The most likely one regards the formation of solids by co-crystallization, or in other words, by a thermal fractionation of the blend (Chen, Lai, Ghazali, & Ghong, 2002). When vegetable oils containing TAGs with different melting points are cooled, the higher-melting point TAGs promptly phase out generating solid crystals in a liquid phase of low melting point TAGs. In isotherms obtained below 21.9  C, Chen et al. (2002) reported different consecutive crystallization events in palm oil, with the formation of two solid fractions. The first, composed by stearin (higher melting point TAGs) and the second one by olein (lower melting point), crystallized with different induction times. The second possible mechanism concerns the occurrence of a polymorphic transition during the initial part of the cooling process. Bootello et al. (2013) studied two-steps crystallization profile of confectionery fats and found that the first step was due to a quick formation of metastable crystals and the second step was related to polymorphic transitions from a less stable to the more stable b or b0 polymorphs. However, the authors pointed out that some systems are able to fractionate and form different solid solutions and in order to establish the nature of the second step, it would be necessary to conduct an isothermal crystallization test, monitored by XRD. Verstringe, Danthine, Blecker, Depypere, and Dewettinck (2013) showed that high degree of supercooling also promotes a two-step crystallization in palm oil, with a crystals formed in the first step, which in turn are transformed into b0 1 crystals in the second step. They also reported that b0 1 crystals can be formed directly from the melt, and, furthermore, palm oil can directly crystallize into the b0 1 polymorph when submitted to lower degree of supercooling. Three different events are involved in the process of crystallization, as follows: nucleation, crystal growth and maturation of crystals. The induction time, tSFC, is inversely proportional to the nucleation rate. The induction time of the crystals and the maximum solid fat content were obtained by inspection of the curves and the data are presented in Table 1. The results confirmed that the addition of PKO, at any level, did not modify the crystallization behavior at all, in terms of, tSFC, and SFCmax. A possible explanation for this behavior is the predominance of medium chain fatty acids found in this hydrogenated product. The effect of the additive with shorter chains decreases more rapidly than those that present similarity with the carboxyl chains of the fatty acids present in the lipid system (Smith, Bhaggan, Talbot, & Malssen, 2011). To quantify the crystallization rate and to qualify the crystals growth, the Avrami Equation (Equation (1)) was fitted to the experimental data. The values obtained for the Avrami constant B (min-n), Avrami exponent, n, and the correlation coefficient, R2, are also given in Table 1.

Please cite this article in press as: de Oliveira, G. M., et al., Hard fats as additives in palm oil and its relationships to crystallization process and polymorphism, LWT - Food Science and Technology (2015), http://dx.doi.org/10.1016/j.lwt.2015.04.036

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Table 1 Induction time, tSFC ; solid fat content at equilibrium, SFCmax; Avrami constant, B, Avrami exponent, n, determination coefficient, R2, obtained after static crystallization at 25  C for palm oil and palm oil added with PKO, PO, CO, SO and CR. Sample Palm oil PKO

PO

CO

SO

CR

1 3 5 1 3 5 1 3 5 1 3 5 1 3 5

g/100 g/100 g/100 g/100 g/100 g/100 g/100 g/100 g/100 g/100 g/100 g/100 g/100 g/100 g/100

g g g g g g g g g g g g g g g

tSFC (min)

SFCmax (g/100 g)

B (minn)

n

R2

34 34 34 30 26 15 11 23 15 10 22 12 9 14 6 5

10.1 9.8 9.7 10.2 11.1 13.1 15.1 11.0 12.6 14.9 10.7 12.6 14.8 9.9 11.5 13.2

7.0E-08 1.6E-08 4.6E-08 1.1E-07 1.2E-07 2.1E-05 2.4E-04 1.8E-07 1.7E-04 4.1E-04 4.7E-07 3.3E-05 9.8E-05 2.3E-05 2.3E-03 8.0E-03

4.0 4.4 4.0 3.9 4.0 3.1 2.7 4.1 2.5 2.6 3.8 3.1 3.1 2.9 2.0 1.7

0.98 0.97 0.98 0.98 0.99 0.97 0.98 0.99 0.99 1.00 1.00 0.94 0.87 0.96 0.98 0.86

PKO, fully hydrogenated palm kernel oil; PO, fully hydrogenated palm oil; CO, fully hydrogenated cottonseed oil; SO, fully hydrogenated soybean oil; CR, fully hydrogenated crambe oil. Means of duplicate analyses are reported.

Blends of palm oil with PO, CO, SO and CR (1 g/100 g) provided a significant effect in reducing the induction time of crystallization, decreasing tSFC from the original 34 min to 26, 23, 22 and 14 min, respectively. At this low level of addition, the influence of the hard fats on SFCmax was negligible. The behavior found for the additives can be related to the physical characteristics of the predominant alkyl chain in the hard fats. Aliphatic chains as those corresponding to C16:0 and C18:0 show higher melting points and are similar to the alkyl chain found in palm oil. Therefore, they will be more influential on the crystallization properties favoring the decrease of the induction time of the samples. This decreasing trend was observed in all blends. According to Sato (2001), specific molecular interactions between the crystallization modifiers materials and, the lipid to be crystallized are prerequisites for the modulation effect of the process. Similarity in terms of aliphatic chain, involves two meanings: the chain length and the chemical structure of the fatty acids. Himawan, Starov, and Stapley (2006), indicated that significant changes in crystallization behavior are obtained when the fatty acid chain lengths of the components added differ at most by four carbon atoms with respect to the predominant fatty acid in the mother phase. The presence of C20:0 and C22:0 in CR promoted significant changes in the crystallization pattern of palm oil. Blends with this hard fat presented a significant change in the tSFC of palm oil, providing the shortest time of the crystal induction, especially the blend with CR at 5 g/100 g, which was able to reduce the beginning of the crystallization to only 5 min. Moreover, increasing concentration of CR in the sample increased the SFCmax although in lesser extent as when hard fats in which C16:0 and C18:0 are predominant. This is clearly the case in blends with PO, CO, SO and CR at 5 g/ 100 g. The data in Table 1 indicate that with PO at 5 g/100 g, the SFCmax increased 50.4% compared to palm oil, and the corresponding increase with CR at 5 g/100 g was only 31.3%. The results indicate that the influence of the CR on the nucleation process outstands its effect on crystal growth. The derivation of the Avrami equation is based on solid physical principles and requires n to be an integer, but fractional values, as found here, are usually obtained. According to Marangoni (2005), these values are found in situations of simultaneous development of two or more types of crystals, or similar crystals built up from different nuclei, in sporadic or instantaneous way. Based on this judgment, values of n close to 4 indicate the predominance of spherulitic growth from sporadic nuclei, as obtained by the sample

of palm oil and all its blends with PKO, and blends with PO, CO and SO at concentration of 1 g/100 g. Blends with CR (1 g/100 g), and blends with PO, CO and SO at 3 g and 5 g/100 g, scored values of n between 2.5 and 4, indicating the presence of a mixture of spherulites and of disk-type crystals, also grown from instantaneous or sporadic nuclei. However, blends of palm oil with CR at 3 and 5 g/ 100 g were the only ones with n closed to 2, an indicator of disktype growth with instantaneous nucleation. The microstructure images presented in the previous work (Oliveira, Ribeiro, & Kieckbusch, 2015) corroborate the existence of these crystals, indicating that the CR had a strong influence on the nucleation stage, increasing the number of nuclei, and decrease the induction time of nucleation and therefore leading to the formation of very small crystals. The crystallization rate constants, “B”, obtained for the blends, indicate an increasing trend with the addition of hard fats, being significant in blends with SO, CO and PO. This property point out that the addition of these hard fats to palm oil enhances the crystallization process and can avoid the formation of crystalline clusters in post-processing stages. Once again, the blends with PKO did not promote changes in “B”. 3.2. Thermal behavior by differential scanning calorimetry (DSC) The crystallization curves via DSC for palm oil and its blends containing hard fats are presented in Fig. 2, wherein the exothermic heat flux is plotted as a function of temperature. The crystallization parameters derived from the thermal curves are shown in Table 2. The selected parameters include: onset temperature (Toc), which refers to the start of the phase transition; peak temperature of crystallization (Tc), wherein the thermal effect is maximum; enthalpy of crystallization (DHc) or phase transition enthalpy, measured by the area under the curve; and offset temperature of crystallization (Tof), which indicates the conclusion of the thermal effect (Ribeiro, Basso, Grimaldi, Gioielli, & Gonçalves, 2009). Palm oil presented two crystallization peaks reflecting the separation of the lipid content in two distinct fractions. The fraction of high melting point TAGs, composed by trisaturated TAGs and higher melting point disaturated TAGs, melt at higher temperatures and formed the first peak of the thermal output; complementarily, the soft fractions rich in unsaturated fatty acids, correspond to low melting point TAGs were responsible for the second crystallization peak. This profile is consistent with the chemical composition of palm oil reported in the first part of this paper (Oliveira, Ribeiro,

Please cite this article in press as: de Oliveira, G. M., et al., Hard fats as additives in palm oil and its relationships to crystallization process and polymorphism, LWT - Food Science and Technology (2015), http://dx.doi.org/10.1016/j.lwt.2015.04.036

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5

Fig. 2. Crystallization curves obtained by DSC of palm oil and palm oil added with hard fat of PKO, fully hydrogenated palm kernel oil; PO, fully hydrogenated palm oil; CO, fully hydrogenated cottonseed oil; SO, fully hydrogenated soybean oil; CR, fully hydrogenated crambe oil, at 1 g/100 g (d), 3 g/100 g (‒∙‒) and 5 g/100 g (‒ ‒).

et al., 2015), with the trisaturated TAGs summing up 15.7 g/100 g of the total TAGs. The solidification of this fraction of trisaturated TAGs released an amount of heat corresponding to an enthalpy difference of 9.3 J/g. The energy dissipated in the second crystallization peak is larger than in the first peak (34.7 J/g). The PKO, PO, CO, SO and CR are composed only by trisaturated TAGs and consequently, form a single peak in the DSC crystallization curves (Ribeiro, Basso, Santos, et al., 2013). These hard fats

added to palm oil, in turn, showed a distinct influence on the crystallization behavior. The curves in Fig. 2 confirm that the addition of hard fats promoted an acceleration of the crystallization events, proportional to the amount of PO, CO, SO and CR added to the samples. Table 2 indicates that onset temperatures found were higher by more than 6  C in blends of palm oil with SO, CO or PO at 5 g/100 g confirming the decrease of the initial time of crystallization process. As expected, blends with CR at 3 g and 5 g/100 g

Table 2 Thermal crystallization behavior of palm oil and palm oil added with PKO, PO, CO, SO and CR. Onset temperature of crystallization (Toc ( C)), peak temperature of crystallization (Tpc ( C)), enthalpy of crystallization (DHc (J/g)), and offset temperature (Tof ( C)). Sample

Toc ( C)

Palm oil PKO 1 3 5 PO 1 3 5 CO 1 3 5 SO 1 3 5 CR 1 3 5

18.9 18.8 19.2 19.5 20.7 23.5 25.1 20.7 24.2 25.7 20.8 25.0 27.6 23.0 30.7 35.1

Peak 1 g/100 g/100 g/100 g/100 g/100 g/100 g/100 g/100 g/100 g/100 g/100 g/100 g/100 g/100 g/100

g g g g g g g g g g g g g g g

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.5J 0.2J 0.2iJ 0.3i 0.1h 0.1g 0.2de 0.1h 0.0f 0.2d 0.2h 0.1e 0.2c 0.2g 0.1b 0.1a

DHc (J/g)

Tpc ( C)

16.2 16.9 17.1 17.1 18.0 21.1 22.8 18.4 22.7 23.4 18.5 22.6 25.5 19.4 27.3 32.9

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

Peak 2 0.3k 0.1j 0.0j 0.0j 0.1i 0.1f 0.0e 0.1hi 0.2e 0.1d 0.0h 0.0e 0.0c 0.3g 0.1b 0.1a

0.8 0.1 0.2 0.3 0.0 0.1 0.1 0.1 0.4 0.0 0.1 0.1 0.1 0.3 0.4 0.3

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

0.2f 0.2bcde 0.1de 0.1de 0.2abcd 0.1bcde 0.0bcde 0.0abcd 0.3a 0.2abcd 0.1abc 0.1abcd 0.1bcde 0.1de 0.2ef 0.2ab

Intermediate peak

Peak 1

Nd Nd Nd Nd Nd Nd Nd Nd Nd Nd Nd Nd Nd Nd Nd 19.8 ± 0.0a

9.3 10.2 9.4 9.7 9.7 11.5 13.4 10.1 10.1 13.1 9.9 11.5 12.6 8.6 8.2 4.0

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

Tof ( C) Peak 2

0.2f 0.1d 0.2f 0.1ef 0.1ef 0.1c 0.2a 0.2de 0.3de 0.3ab 0.2de 0.1c 0.2b 0.1g 0.1g 0.1h

34.7 42.3 37.1 36.9 35.7 36.9 36.8 39.0 33.7 36.2 36.9 37.9 34.7 36.2 31.2 32.9

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

Intermediate peak 0.6fed 0.7a 0.4bcd 1.1bcd 0.3cde 0.5bcd 0.7bcd 0.2b 0.7efg 1.5cde 0.5bcd 0.5cb 0.6fed 2.5cde 0.3g 0.1fg

Nd Nd Nd Nd Nd Nd Nd Nd Nd Nd Nd Nd Nd Nd Nd 5.26 ± 0.07a

33.0 35.2 32.6 32.1 32.4 30.9 31.0 32.3 29.9 30.5 31.3 30.6 29.2 34.0 34.0 29.8

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

1.69fde 0.9e 0.6bcde 0.4abcde 0.3bcde 0.2abcd 0.5abcd 0.3abcde 0.7abc 0.5abc 0.8abcd 0.5abc 0.7a 2.4de 2.4de 0.6ab

Values are shown as mean ± standard deviation of three replications. Means with different letters within the column indicate that the samples are statistically different (P < 0.05) by Tukey's test. PO, palm oil; PKO, fully hydrogenated palm kernel oil; PO, fully hydrogenated palm oil; CO, fully hydrogenated cottonseed oil; SO, fully hydrogenated soybean oil; CR, fully hydrogenated crambe oil. Nd: Not detected.

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have the highest Toc, being 16.2 and 11.8  C higher than pure palm oil, respectively. Similar behavior was found for the maximum temperature of the first peak. Most of the blends of palm oil with hard fats showed similar thermal events, displaying two crystallization peaks. Palm oil added with CR at the concentration of 3 g/100 g and 5 g/100 g, however, tended to split the first peak in two, suggesting a segregation of the trisaturated TAGs with higher melting points from the CR, and the trisaturated and disaturated TAGs from palm oil. Verstringe et al. (2013) evaluated, also with a DSC, the crystallization behavior of palm oil added with monopalmitin. The authors found that low concentrations of this additive promoted the crystallization of the higher-melting point TAGs present in palm oil, followed by the crystallization of the low melting point TAGs. However, the samples with higher concentrations of monopalmitin (>4 g/100 g) induced a fractional crystallization of the fat. Similar mechanism can be assumed with the CR added blends and is related to the degree of supercooling. At 1 g/100 g of this hard fat in palm oil induced the crystallization of the higher melting point TAGs in the system, promoting a decrease of the nucleation period. The second transition event (2nd peak), involves the crystallization of partly or fully unsaturated TAGs and are not necessarily favored by the addition of CR. Concentrations of 3 and 5 g/100 g of blends with CR intensify the nucleation stage, but the crystallization of these components is so fast that caused the segregation of the lipid fractions. Furthermore, it is possible that the molecular dissimilarity between fatty acids present in CR and in palm oil encourages the separation of the species when subjected to a supercooling. Again, there was a negligible effect of the PKO addition on thermal behavior of palm oil, and Fig. 2 shows the strong similarity between the curves of palm oil and of its blends with PKO. The thermal behavior by DSC indicated that blends did not promote segregations at all concentrations of PO, CO and SO, and

with CR at 1 g/100 g, ratifying these components as seed crystals. Moreover, hard fats can produce an structuration effect in a lipid system, and the development of products with zero trans fat and low contents of saturated fatty acids added with this additive are been investigated (Oliveira, Stahl, Ribeiro, et al., 2015). 3.3. Polymorphism The X-ray diffraction technique is a universal procedure for determination of the polymorphic form of the crystalline material. The atoms of TAGs molecules have regular distances between themselves and cause a characteristic wavelength dispersion, enabling the identification of polymorphic forms based on diffraction patterns already established and well documented. Fig. 3 shows the diffraction peaks and short spacings evaluated at 25  C for palm oil and blends with hard fats. Therefore, at 25  C, no sample exhibited fully crystalline structures because some triglycerides show lower melting point. In order to minimize interpretation errors of these structures and to prove the existence of the predicted crystal habits, the blends with SO and CR were also evaluated by X-ray diffraction at 20  C, to avoid random atomic arrangements (Fig. 4). Palm oil, in its natural form, is exclusively in the b0 form with short spacings 0.42 and 0.38 nm (Fig. 3A). The b0 polymorph in palm oil can be attributable to the large amount of TAGs with 50 and 52 carbons (80.4 g/100 g), as PSP and PSS, which arrange as b0 crystals. Furthermore, deMan and deMan (2001) reported that certain factors can positively influence the formation of b0 crystals such as, high levels of C16:0, diversity in the fatty acids profile and TAG composition, the amount of liquid oil in the matrix and the presence of PSP, since this TAG itself does not stabilize in a b polymorph. Accordingly, the position of specific fatty acids in the glycerol molecule induces the predominant crystallization form. In general, fats which contains asymmetric TAGs show a tendency for the crystallization in the Form b0 , while the symmetrical TAGs favor

Fig. 3. XRD patterns obtained after static crystallization at 25  C for palm oil (A) and palm oil added to hard fats of (B) PKO, fully hydrogenated palm kernel oil; (C) PO, fully hydrogenated palm oil; (D) CO, fully hydrogenated cottonseed oil; (E) SO, fully hydrogenated soybean oil; and (F) CR, fully hydrogenated crambe oil.

Please cite this article in press as: de Oliveira, G. M., et al., Hard fats as additives in palm oil and its relationships to crystallization process and polymorphism, LWT - Food Science and Technology (2015), http://dx.doi.org/10.1016/j.lwt.2015.04.036

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Determinations by X-ray diffraction patterns at 25  C (Fig. 3E and F) indicated that b0 polymorph was predominant in the crystalline composition of the samples with SO, while in those with CR the b form prevailed. In addition, Fig. 3F, suggests a balance between the amount of the crystals b and b0 in the blend with CR at 5 g/100 g. However, at 25  C is a temperature close to the melting point of the b0 crystals, maintaining the higher melting point b crystals. Nevertheless, the Fig. 4A and B, corroborate a predominance of b0 crystals in these blends. To ensure the stability of the polymorph b0 in products formulated with palm oil is an issue of great industrial interest. Steadying the b0 form and reducing the size crystals enable the incorporation of a larger amount of liquid oil in the crystal network, promoting a bright and uniform surface and even a soft texture. This fat profile contributes to the use of palm oil in margarine and shortenings. Additionally, the incidence of b crystals favors the use of palm oil as ingredient in cocoa butter alternatives. 4. Conclusions

Fig. 4. XRD patterns obtained after static crystallization at 20  C for palm oil added to hard fats of (A) SO, fully hydrogenated soybean oil and, (B) CR, fully hydrogenated crambe oil.

Increasing addition of saturated triacylglycerols present in hard fats of palm, cottonseed, soybean and crambe oils induces significant changes in the crystallization behavior of palm oil, leading to a significant increment in the rate of crystallization and in the maximum solid fat content. Triacylglycerols containing longer aliphatic chains like C16:0, C18:0 and C22:0, prove to be influential additives, favoring the decrease of the nucleation time of the blends and influence changes in the polymorphism of palm oil. Determinations by X-ray diffraction patterns indicated that the induction of b crystal during the crystallization of palm oil is possible by the addition of certain groups of TAGs with preferential b crystallization as templates. Therefore, at 25  C the blends with palm kernel, palm and cottonseed hard fats produce exclusively b0 form crystals and, mixtures of b and b0 crystals are observed in samples of palm oil with soy and crambe hard fats. Adding hard fats of palm, cottonseed, soybean and crambe oils to palm oil reveal to be beneficial due to an increase of its compatibility for possible uses in cocoa butter alternatives and fat-based products. Fully hydrogenated palm kernel oil has no influence in palm oil crystallization events.

b crystals formation. Along this line, the specific chemical compo-

Acknowledgments

sition of palm oil established its polymorphic behavior, even as in blends with PKO, PO and CO, which also presented exclusively b0 form crystals (Fig. 3B, C, and D). Therefore, mixtures of b0 and b forms were detected in the blends of palm oil with SO and CR. Multicomponent materials as fats tend to exhibit a mixture of crystal types, affecting significantly the polymorphic transitions. According to Bergel (2001), fully hydrogenated fats, with a predominance of 18 carbon atoms fatty acids, show a tendency to develop b crystals. The SO presented 63.8 g of tristearin (SSS-C54) and 87.2 g of C18:0 per 100 g of product that promoted the formation of b crystals with 0.46 nm of short spacing, and PSS type TAG, which in turn, favored the appearance of b0 crystals. Besides, SO has shown to crystallize as a mixture of b0 and b crystals (Ribeiro, Basso, Santos, et al., 2013). In sequence, the polymorphic habits of CR blends were related to their heterogeneous TAG composition. Although, CR shows almost solely, long-chain fatty acids with high melting point, there is a certain degree of variation among them, causing heterogeneity in the TAG composition; complementarily there is an asymmetry in some of these TAGs in CR as PSBe, SSBe, SABe and SBeBe. Almost certainly this distinct composition determined the appearance of a blend of b0 and b forms.

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Please cite this article in press as: de Oliveira, G. M., et al., Hard fats as additives in palm oil and its relationships to crystallization process and polymorphism, LWT - Food Science and Technology (2015), http://dx.doi.org/10.1016/j.lwt.2015.04.036