Engineering the microstructure of milk fat by blending binary and ternary mixtures of its fractions

Abstract

In this study, the microstructure and crystallization kinetics of binary and ternary mixtures of milk fat fractions during isothermal crystallization at 5, 15, and 20 °C were characterized using polarized light microscopy and the Avrami model. Results showed that for both binary and ternary mixtures, high concentrations of the high-melting fraction result in the formation of rod or needle-like crystals (i.e., one-dimensional growth and low values of Avrami index, n) while at relatively higher concentrations of the middle-melting and low-melting fractions, multi-dimensional crystal growth is favored (i.e., higher n values). On the effect of temperature, for binary mixtures, it was found that at high undercooling conditions (5 °C) one dimensional growth is favored while for ternary mixtures, increasing the crystallization temperature (i.e., decreasing supersaturation) from 15 to 20 °C results in large differences in crystal structure. Mechanisms for the observed behavior are also suggested.

---

1. Introduction

Milk fat is composed of about 98% triacylglycerols (TAGs) of extreme heterogeneity which brings about its complex thermal behavior (i.e., melting points of −40 to 40 °C).^1,2 With the use of differential scanning calorimetry (DSC), the melting of milk fat was shown to exhibit three overlapping peaks which are related to the melting of the different milk fat fractions classified as low-melting fraction (LMF), middle-melting fraction (MMF) and high-melting fraction (HMF).^3,4 Milk fat is composed of 11% HMF which has a melting point (MP) greater than 50 °C, 23% MMF (MP = 35–40 °C) and 66% LMF (MP > 15 °C). HMF consists mainly of long chain saturated fatty acids (FAs); MMF consists of long chain and short chain FAs; and LMF is composed mainly of short chain and unsaturated FAs.^5–8 Several methods have been developed to separate the fractions from milk fat such as dry and solvent fractionation.^3,5,8 Furthermore, studies have been performed to describe the phase behavior and crystallization behavior (e.g., polymorphism) of these fractions and their mixtures.^8–10

In studying crystallization kinetics, Avrami parameters are often used as they provide information on both nucleation and crystal growth. By measuring solid fat content (SFC) in time during isothermal crystallization at a given temperature, Avrami parameters such as the Avrami constant, k, and exponent, n can be determined. The Avrami constant, k, is the rate constant of crystallization which follows an Arrhenius-type dependence with crystallization temperature. On the other hand, the Avrami exponent, n, sometimes also called crystallization index, provides information on the type of nucleation and crystal growth.^11–14 Table 1 shows the possible values of n, and the corresponding type of nucleation and growth.

Table 1 Values of the Avrami exponent, n, and the corresponding type of nucleation and growth adapted from Wright & Marangoni (2003)¹⁶

Avrami exponent, n	Type of nucleation and growth
1 + 0 = 1	1D growth from instantaneous nuclei
1 + 1 = 2	1D growth from sporadic nuclei
2 + 0 = 2	2D growth from instantaneous nuclei
2 + 1 = 3	2D growth from sporadic nuclei
3 + 0 = 3	3D growth from instantaneous nuclei
3 + 1 = 4	3D growth from sporadic nuclei

---

The microstructure of milk fat has been shown to affect the rheological and sensorial properties of milk fat-containing products.^15–17 Milk fat fractions have also been used in different food applications to provide structure and specific functionality such as the prevention of bloom formation in chocolate upon addition of HMF.^18,19 It is therefore important to characterize the microstructure formed by various mixtures of the high, middle and low-melting fractions at different crystallization temperatures to be able to create a database of different crystallization behaviors and crystal forms for different product applications.

In this article, the crystallization kinetics of binary and ternary mixtures of milk fat fractions (i.e., LMF, MMF and HMF) is characterized using the Avrami model, and these kinetics are related to the resulting microstructure of milk fat.

2. Experimental

2.1. Milk fat fractions

Milk fat fractions were separated by multi-step solvent (ethyl acetate) extraction as described by Marangoni & Lencki (1998).⁸ The fractions were then melted and binary and ternary mixtures were obtained by manually mixing and combining the fractions on a w/w basis.

2.2. Crystallization kinetics

The crystallization behavior of various mixtures of the LMF, MMF and HMF of milk fat were studied by measuring SFC as a function of time at different isothermal temperatures using a Bruker pulsed nuclear magnetic resonance (pNMR) analyzer unit PC20 Series (Brucker, Milton, Canada).

The samples were first heated to 80 °C for 30 min prior to analysis in order to destroy any thermal history. They were then placed in a water bath set at the following crystallization temperatures: 5, 15 and 20 °C (i.e. isothermal crystallization) and solid fat content was measured at given time intervals (every 20 to 30 seconds for 10 to 60 minutes).

The Avrami equation^11–13,20 was used to quantify the kinetics of crystallization,

where n is the Avrami exponent; k is the Avrami constant; SFC_(t) is the solid fat content at a particular time; and SFC_(max) is the maximum solid fat content at a given temperature (indicated by a plateau). Nonlinear regression was then carried out using GraphPad Prism (GraphPad Software, San Diego, CA, USA).

2.3. Polarized light microscopy (PLM)

To be able to relate the crystallization kinetics of milk fat with microstructure, the different mixtures of LMF, MMF, and HMF were observed under PLM. Samples were initially heated to 80 °C for 30 min to destroy all traces of crystal memory. A small drop of molten fat was then applied onto a heated microscope slide and covered using a heated coverslip. Samples were then allowed to crystallize isothermally for a week at 5, 15 and 20 °C incubators.

Samples were then observed under polarized light using an Olympus BH light microscope (Olympus, Tokyo, Japan). A Sony XC-75 CCD camera in “autogain” mode (Sony, Tokyo, Japan) was used to take photographs of the samples. Images were then normalized, and the contrast and grayscale were standardized using The Image Processing Tool Kit software (Reindeer Graphics, Inc., Asheville, North Carolina, USA).

3. Results and discussion

The microstructure of milk fat can be engineered by judicious combination of milk fat fractions and crystallization at different temperatures. Binary and ternary mixtures of milk fat fractions – HMF, MMF and LMF, were prepared at different concentrations and were crystallized at 5, 15 and 20 °C. The Avrami exponent, n and SFC_max were then calculated using eqn (1).

3.1. Binary mixtures

3.1.1. High-melting fraction (HMF) and middle-melting fraction (MMF). Fig. 1 shows n and SFC_max values of HMF–MMF mixtures at 5, 15 and 20 °C. At 5 °C, it can be observed that n and SFC_max values do not greatly change with increasing HMF content. n values ≤1 indicate a rod or needle-like growth from instantaneous nuclei (Fig. 2a). Moreover, at low temperatures, both HMF and MMF are mostly in their solid states. HMF and MMF consist of mostly saturated FAs (i.e., C16:0 and C18:0).⁸ Thus, crystallization at low temperatures leads to the formation of numerous small rod-shaped crystals.

Fig. 1 Avrami exponent, n and measured maximum solid fat content (SFC_max) values as a function of HMF concentration, obtained from the fitting of the isothermal crystallization curves of binary mixtures of HMF and MMF at 5, 15 and 20 °C.

Fig. 2 Polarized light (PLM) micrographs of binary mixtures of HMF and MMF crystallized isothermally: (a) 90% HMF : 10% MMF at 5 °C (n ∼ 1) and (b) 10% HMF : 90% MMF (n ∼ 1.5) at 20 °C. Scale bar corresponds to 100 μm.

By creating a binary phase diagram of mixtures of HMF and MMF, Marangoni & Lencki (1998)⁸ found a monotectic phase behavior between the two fractions. That is, although HMF and MMF differ somewhat in melting points and molecular volume, their structural complementarity makes them miscible in the solid state. They were also found to have the same β′ polymorphism. Therefore during crystallization, mixed crystals of HMF and MMF are formed. This monotectic behavior can be observed in our study as indicated by an instantaneous nucleation (i.e., both HMF and MMF TAGs can be starting nucleus for each other), high SFC, and uniformity in crystal morphology and size was observed.

Binary systems of HMF and MMF at 15 and 20 °C (Fig. 1) show a general trend where the n value decreases while SFC increases as the HMF concentration increases. It can be observed that n values decrease from 1.5 to 1 which indicates a transition from two dimensional to one dimensional growth and instantaneous nucleation. It is expected that both nucleation and crystal growth occur simultaneously when cooling HMF and MMF, even at high cooling temperatures, due to the high amounts of saturated FAs present in these fractions. However, it can be observed that not only rod-shaped crystals are formed but small and big spherulites as well at lower HMF concentrations (e.g., 10% HMF : 90% MMF at 20 °C) (Fig. 2b). Spherulitic growth may not necessarily mean spherical growth as it could be 1 or 1.5 dimensional growth as indicated by the calculated n values (n ≤ 2). Spherulitic growth arises under highly non-equilibrium conditions, where one dimensional growth is favored, however, the final mesoscale growth looks spherical probably due to diffusional limitations.^21–23 That is, the viscosity becomes very high too quickly that crystallite diffusion and aggregation is impaired. Meanwhile, molecular diffusion is also reduced while crystallization rate increases dramatically. These combined effects result in crystals growing simultaneously from a common center, resulting in spherulitic morphology. Under these highly non-equilibrium conditions, spherulitic growth is favored. It is important to remember that spherulitic growth does not equal spherical growth even though the structures look spherical under the microscope. The effect of HMF concentration on SFC can be better observed at higher crystallization temperatures. This is because at 20 °C, most of the MMF is in the liquid phase (short chain FAs) and therefore SFC becomes dependent on the solid HMF at high temperatures.

3.1.2. Isothermal crystallization of mixtures of high-melting fraction (HMF) and low-melting fraction (LMF) at 5, 15 and 20 °C. In binary systems of HMF and LMF crystallized statically at 5, 15 and 20 °C (Fig. 3), the same trend as that of HMF and MMF mixtures (i.e., 15 and 20 °C) can be observed where n values decrease and SFC_max values increase as the concentration of HMF is increased (i.e., while subsequently decreasing the concentration of LMF). However, larger differences are observed in HMF–LMF mixtures, as LMF is affected greatly by the temperatures studied in this project.

Fig. 3 Avrami exponent, n and measured maximum solid fat content (SFC_max) values as a function of HMF concentration, obtained from the fitting of the isothermal crystallization curves of binary mixtures of HMF and LMF at 5, 15 and 20 °C.

In terms of microstructure, it can be observed that more crystalline mass and bigger crystals are observed as the mixture is enriched with HMF and decreased of LMF, especially at a higher crystallization temperature of 20 °C (Fig. 4a). The n value decreased to 1 as more HMF was added to the system, indicating that increasing HMF forces TAGs to crystallize in a one-dimensional manner from instantaneous nuclei. As HMF is composed of TAGs with high melting points (>50 °C),⁸ this forces nucleation to occur instantaneously at these temperatures. The undercooling is very high, which translates to large driving force for both nucleation and growth. On the other hand, increasing concentration of LMF in the system favors three-dimensional, spherical growth from sporadic nuclei especially at higher crystallization temperatures (Fig. 4b). Growth of crystals in a multi-dimensional form at higher temperatures could be explained by two factors. First, the presence of liquid fat provides free volume and mobility (lower viscosity, higher diffusivity) for the crystals and second, as the supersaturation is decreased, crystallization occurs slower which results in the formation of larger crystals. According to Marangoni & Ollivon (2007),²⁴ these spherulites fall into category 1, in which spherulites grow radially from a nucleus and continuously branch out to maintain a space-filling character. As the mass fraction of solids decreases (lower supersaturation and lower SFC), crystal growth is favored which results in the observed larger spherulites. On the other hand, the observed difference in nucleation (i.e., sporadic vs. instantaneous) which leads to the heterogeneous size distribution of the crystals is more complex, and may be affected by purity and other complex factors.

Fig. 4 Polarized light (PLM) micrographs of binary mixtures of HMF and LMF crystallized isothermally at 20 °C: (a) 90% HMF : 10% LMF (n ∼ 1) and (b) 10% HMF : 90% LMF (n ∼ 3). Scale bar corresponds to 100 μm.

According to Marangoni and Lencki (1998),⁸ HMF and LMF mixtures show eutectic mixing which shifts to monotectic systems when melting point differences of the two components increase, and a considerable amount of the low melting component is dissolved by the high melting component. This therefore results in the formation of a partial solid solution. This behavior was confirmed by Wright et al. (2000),²⁵ where LMF was used as a solvent to study the crystallization behavior of HMF and MMF. Using X-ray diffraction, they were able to detect the presence of liquid crystalline structures that increase SFC of the systems. At higher crystallization temperatures, LMF acts mainly as a diluent for the solid HMF, which allows for the observed spherical growth of the HMF (e.g. 10% HMF : 90% LMF at 20 °C). This is important as shown in studies by Mazzanti et al. (2004)⁹ where a binary mixture of HMF and LMF results in the formation of stable β crystals. On the other hand, at lower temperatures (i.e., 5 °C), a monotectic behavior is suggested where high amounts of LMF is incorporated in the HMF crystals, due to the structural complementarity of the TAGs present in these fractions as well.

3.1.3. Isothermal crystallization of mixtures of middle-melting fraction (MMF) and low-melting fraction (LMF) mixtures at 5 °C. Results in Fig. 5 show the crystallization behavior of binary mixtures of MMF and LMF at 5 °C. Due to the high amount of liquid oil present in this mixture at higher crystallization temperatures, crystallization behavior was only studied at 5 °C. Results show that the n values decrease while SFC_max values increase as MMF concentration is increased. In relation to microstructure, it was found that more crystalline mass is formed as the concentration of MMF is increased. Furthermore, at high concentrations of LMF, it was found that small spherulites are formed while at high MMF concentrations (i.e., lower LMF), small rod or needle-shaped crystals are formed.

Fig. 5 Avrami exponent, n and measured maximum solid fat content (SFC_max) values as a function of MMF concentration, obtained from the fitting of the isothermal crystallization curves of binary mixtures of MMF and LMF at 5 °C.

3.2. Ternary mixtures

3.2.1. Varying concentrations of the high-melting (HMF) and middle-melting fractions (MMF) while keeping the low-melting fraction (LMF) constant at 10% and 50% (w/w) during isothermal crystallization at 15 and 20 °C. Fig. 6 shows results of the isothermal crystallization of the ternary system of HMF, MMF and LMF at 15 °C and 20 °C. Composition was varied by increasing the concentration of HMF (subsequently decreasing that of MMF) and keeping LMF at 10% and 50%. At 15 °C and 10% LMF, it can be observed that the n values do not increase beyond 1.5, which suggests that crystals grow in a rod-like manner from an instantaneous or sporadic nuclei.¹⁴ This corresponds well with the microstructure presented in Fig. 7a. On the other hand, at 20 °C, spherulitic or disc-like crystals appear at 10% HMF, 80% MMF and 10% LMF (n ∼ 2) (Fig. 7b). As explained in Section 3.1.2, it can be observed again that spherulitic growth may not necessarily mean spherical growth as it could be 1 or 1.5 dimensional growth due to diffusional limitation and as indicated by the calculated n value (n ≤ 2).

Fig. 6 Avrami exponent, n and measured maximum solid fat content (SFC_max) values as a function of HMF concentration, obtained from the fitting of the isothermal crystallization curves of ternary mixtures of HMF, MMF and LMF at 5, 15 and 20 °C.

Fig. 7 Polarized light (PLM) micrographs of ternary mixtures of HMF, MMF and LMF crystallized isothermally: (a) 50% HMF : 40% MMF : 10% LMF at 15 °C (n ∼ 1) and (b) 10% HMF : 80% MMF : 10% LMF at 20 °C (n ∼ 2). Scale bar corresponds to 100 μm.

Keeping LMF at 50%; results show low SFC_max values (<40%) at 15 °C and 20 °C (Fig. 6). n values decrease from 3.5 to 1 as the HMF concentration is increased, suggesting a disc-like to needle-like crystal growth from a sporadic or instantaneous nuclei (Fig. 8a and b).

Fig. 8 Polarized light (PLM) micrographs of ternary mixtures of HMF, MMF and LMF crystallized isothermally at 20 °C: (a) 10% HMF : 40% MMF : 50% LMF (n ∼ 3.5) and (b) 40% HMF : 10% MMF : 50% LMF (n ∼ 1). Scale bar corresponds to 100 μm.

In terms of SFC_max, however, it can be observed that the maximum SFC value reached when HMF is increased to 40% at 20 °C is the same as that at 15 °C; however, no large spherical crystals were observed at 15 °C even at very low SFC_max values. According to Marangoni and Lencki,⁸ crystallization of HMF, MMF and LMF mixtures at 20 °C displays a eutectic behavior at high LMF contents. This means that LMF is pushed out of the mixed crystal and becomes a diluent for the solid structures formed by HMF and MMF, resulting in the growth of large spherical crystals. On the other hand, at 15 °C, a monotectic mixture is formed, which means that LMF crystallizes with HMF and MMF, possibly forming mixed crystal structures therefore no large differences in microstructure were observed.⁸

3.2.2. Varying concentrations of the high-melting (HMF) and low-melting fractions (LMF) while keeping the middle-melting fraction (MMF) constant at 10% and 50% (w/w) during isothermal crystallization at 15 and 20 °C. Fig. 9 shows results for the isothermal crystallization at 15 °C and 20 °C of increasing concentration of HMF, decreasing LMF while keeping MMF constant at 10% and 50%. At 10% MMF, results show a general trend where n values decrease while SFC_max values increase as the HMF concentration is increased. As observed in the previous section, as HMF is increased, small disc-like to large needle-like crystals are formed which correspond well with the calculated n values.

Fig. 9 Avrami exponent, n and measured maximum solid fat content (SFC_max) values as a function of HMF concentration, obtained from the fitting of the isothermal crystallization curves of ternary mixtures of HMF, MMF and LMF at 5, 15 and 20 °C.

The large compatibility between HMF and MMF TAGs allow them to form monotectic structures as that in the large needles; however at high concentrations of LMF (70–80%), small disc-like crystals are formed which is not observed at 15 °C even at the same level of SFC_max. This again shows that at temperatures between 15 and 30 °C, a eutectic mixture is formed, where the LMF transforms or remains in liquid form to allow growth of HMF and MMF solid crystals in all directions.²⁵

On the other hand, in mixtures containing a fixed value of 50% MMF, increasing the concentration of HMF while decreasing LMF at 15 and 20 °C result in decreasing n values and increasing SFC_max (Fig. 9). A larger difference, however, is observed at 20 °C where n decreased from 4 to ∼1 as the concentration of HMF is increased from 20 to 40%. This change corresponds very well with the microstructures shown in Fig. 10a and b where large spherical crystals transform into needle-like structures as the concentration of HMF is increased.

Fig. 10 Polarized light (PLM) micrographs of ternary mixtures of HMF, MMF and LMF crystallized isothermally at 20 °C: (a) 10% HMF : 50% MMF : 40% LMF (n ∼ 4) and (b) 40% HMF : 50% MMF : 10% LMF (n ∼ 1). Scale bar corresponds to 100 μm.

3.2.3. Varying concentrations of the middle-melting (MMF) and low-melting fractions (LMF) while keeping the high-melting fraction (HMF) constant at 10% and 50% (w/w) during isothermal crystallization at 15 and 20 °C. As observed in the previous sections, low concentrations of HMF (10%) result in low SFC_max values (≤40%) although slight increase is observed as the concentration of MMF is increased (Fig. 11). The microstructures observed at 15 °C (Fig. 12a) suggest that the amount of small crystals increases as the concentration of MMF increases. However, the difference in the shape of the crystals is not discernible. At 20 °C, on the other hand, large spherical crystals can be observed even at high concentrations of MMF (Fig. 12b) which correlates well with the high n values (∼1.5 to 6). This could be due to the fact that at 20 °C, most MMF and LMF are in liquid form, and the supersaturation is low, thus allowing crystal growth to proceed from the nucleating HMF.²⁶

Fig. 11 Avrami exponent, n and measured maximum solid fat content (SFC_max) values as a function of MMF concentration, obtained from the fitting of the isothermal crystallization curves of ternary mixtures of HMF, MMF and LMF at 5, 15 and 20 °C.

Fig. 12 Polarized light (PLM) micrographs of ternary mixtures of HMF, MMF and LMF crystallized isothermally: (a) 10% HMF : 70% MMF : 20% LMF (n ∼ 2) and (b) 10% HMF : 70% MMF : 40% LMF (n ∼ 4). Scale bar corresponds to 100 μm.

Keeping HMF constant at 50%, it can be observed that SFC_max remains high at ≥40%, which increases to 60% as the concentration of MMF is increased while the Avrami index, n, remains constant at ∼1 (Fig. 11). These values of n correlate well with the observed microstructures where needle-like crystals are observed.

4. Conclusions

This study shows that the formation of different crystal morphologies from binary and ternary mixtures of milk fat fractions is affected by two factors – crystallization temperature and concentration of the fractions. In binary systems, it was found that at high undercooling conditions (5 °C), supersaturation increases, while the Avrami exponent, n, decreases, indicating the formation of rod or needle-like crystals (one-dimensional growth). On the other hand, under low undercooling conditions (15–20 °C), supersaturation decreases, while n generally increases indicating multi-dimensional crystal growth. This was also found true for ternary systems where lower n values were calculated for systems crystallized at 15 °C than those crystallized at 20 °C.

In terms of concentration of the fractions, crystallization of mixtures of HMF and MMF leads to the formation of small rods or needles, especially at low temperatures (5 °C). Furthermore, at 15 and 20 °C, higher concentrations of HMF result in the formation of large needles, while higher concentrations of MMF (i.e., lower HMF) lead to the formation of large spherulites. These results were also observed in ternary mixtures.

We have thus created a composition–concentration–temperature map that would allow for the targeting of specific milk fat microstructures associated with optimal functionality in food products.

Acknowledgements

The authors would like to acknowledge the financial assistance of the Natural Sciences and Engineering Research Council of Canada (NSERC). The technical assistance of Stephanie Larue-Abecassis is gratefully acknowledged.

References

1. R. E. Timms, Prog. Lipid Res., 1984, 23, 1–38.
2. R. G. Jensen, a. M. Ferris and C. J. Lammi-Keefe, J. Dairy Sci., 1991, 74, 3228–3243.
3. R. E. Timms, Int. J. Dairy Technol., 1980, 47–53.
4. P. S. Dimick, S. Y. Reddy and G. R. Ziegler, J. Am. Oil Chem. Soc., 1996, 73, 1647–1652.
5. G. a. Aken, E. Grotenhuis, a. J. Langevelde and H. Schenk, J. Am. Oil Chem. Soc., 1999, 76, 1323–1331.
6. R. J. Campos, J. W. Litwinenko and A. G. Marangoni, J. Dairy Sci., 2003, 86, 735–745.
7. C. Lopez, F. Lavigne, P. Lesieur, G. Keller and M. Ollivon, J. Dairy Sci., 2001, 84, 2402–2412.
8. A. G. Marangoni and R. W. Lencki, J. Agric. Food Chem., 1998, 46, 3879–3884.
9. G. Mazzanti, S. E. Guthrie, E. B. Sirota, A. G. Marangoni and S. H. J. Idziak, Cryst. Growth Des., 2004, 4, 1303–1309.
10. A. Cisneros, G. Mazzanti, R. Campos and A. G. Marangoni, J. Agric. Food Chem., 2006, 54, 6030–6033.
11. M. Avrami, J. Chem. Phys., 1939, 7, 1103.
12. M. Avrami, J. Chem. Phys., 1940, 8, 212–224.
13. M. Avrami, J. Chem. Phys., 1941, 9, 177.
14. A. J. Wright, R. W. Hartel, S. S. Narine and A. G. Marangoni, J. Am. Oil Chem. Soc., 2000, 77, 463–475.
15. S. S. Narine and A. G. Marangoni, J. Cryst. Growth, 1999, 198–199, 1315–1319.
16. A. J. Wright and A. G. Marangoni, J. Food Sci., 2003, 68, 182–186.
17. A. G. Marangoni, N. Acevedo, F. Maleky, E. Co, F. Peyronel, G. Mazzanti, B. Quinn and D. Pink, Soft Matter, 2012, 8, 1275.
18. S. Sonwai and D. Rousseau, Food Chem., 2010, 119, 286–297.
19. K. E. Kaylegian and R. C. Lindsay, Handbook of Milk Fat Fractionation and Technology Application, AOCS Press, 1995.
20. A. G. Marangoni, Fat Crystal Networks, Marcel Dekker, New York, 2012.
21. L. Granasy, T. Pusztai, G. Tegze, J. A. Warren and J. F. Douglas, Phys. Rev. E: Stat., Nonlinear, Soft Matter Phys., 2005, 72, 1–15.
22. A. Sharples, Polymer, 1961, 3, 250–252.
23. J. H. Magill, J. Mater. Sci., 2001, 36, 3143–3164.
24. A. G. Marangoni and M. Ollivon, Chem. Phys. Lett., 2007, 442, 360–364.
25. A. J. Wright, S. E. McGauley, S. S. Narine, W. M. Willis, R. W. Lencki and A. G. Marangoni, J. Agric. Food Chem., 2000, 48, 1033–1040.
26. A. G. Marangoni and L. H. Wesdorp, in Structure and properties of fat crystal networks, ed. A. G. Marangoni and L. Wesdorp, CRC Press, 2nd edn, 2013, pp. 27–100.

---