Anne-Laure Fameau
Chocolate has played an important role in human culture since about 350 BC, when the Aztecs were drinking fermented cocoa. Today, chocolate gives psychological pleasure all around the world. Chocolate manufacturing is not easy and requires a complex tempering (mixing and heating) procedure to direct the crystallization of cocoa butter (CB) towards the formation of optimal cocoa butter crystals to obtain the good eating quality of chocolate. Besides external factors, crystallization kinetics can be altered by some minor lipidic components and can accelerate or retard the crystal polymorphic transition of TAGs. Recently, Chen et al. used saturated phospholipids to template form V crystal growth in cocoa butter and found that 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) and 1,2-dipalmitoyl-sn-glycero-phosphatidylethanolamine (DMPE) could be utilized as additives, at 0.1% w/w inclusion levels, to engineer the chocolate’s nano- and microstructure [1]. The phospholipid-doped chocolate yielded a product with comparable characteristics to high-quality commercial tempered chocolate without having to resort to complex tempering procedures, including precise shear and temperature regimes. However, the mechanism of action of these phospholipids remained unknown, although it is key to the control and optimization of the new procedure.
In this paper, we determined the structure of self-assembled DMPC in chocolate and its fat phase, cocoa butter, to better understand its effects on the crystallization behavior and polymorphism of cocoa butter. Small-angle neutron scattering studies performed at both ILL on D22 and at ISIS on SANS2D suggested that DMPC forms a variety of micelles in cocoa butter. A strong interaction between the DMPC micelles and the triglyceride palmitoyl-oleoyl-stearoyl glycerol (POS), the most abundant triglyceride in cocoa butter, which also directs the triclinic crystallization of the cocoa butter, was also observed by small-angle X-ray scattering, interfacial tension measurements, and attenuated total reflectance Fourier-transform infrared spectroscopy. This suggested that DMPC micelles serve as a seeding surface, templating form V crystal growth via its effects on POS. We propose a mechanism that involves the DMPC-mediated creation of a nanoscale slip plane within the crystalline lattice, which promotes a solid-state polymorphic transition form IV to V POS in the seeding crystals. Crystal strain and defects were observed in the templated nano- and microstructure observed by synchrotron microcomputed tomography and SAXS, which seemed to propagate across length scales and created micro-cracks in the chocolate. These could affect the product’s properties, suggesting that a simple tempering step may still be required, or another phospholipid structure may be more appropriate. Critically, the addition of specific phospholipids to chocolate will ensure the formation of the correct polymorphic form in the absence of complex tempering procedures, reducing energy and processing costs and allowing for the manufacture of high-quality chocolate by the small chocolatier or large manufacturer alike.
Figure 1: Azimuthally averaged SANS data for 0.5 wt % of d54-DMPC at 25 °C and 80 °C in CB and in 90% dark chocolate. The red line corresponds to the best fit according to a spherical model showing the presence of DMPC micelles in CB at 80 °C.
References:
[1] Chen, J., Ghazani, S. M., Stobbs, J. A., & Marangoni, A. G. (2021). Tempering of cocoa butter and chocolate using minor lipidic components. Nature Communications, 12(1), 5018.
