Visualization of oil migration in chocolate using scanning electron microscopy–energy dispersive X-ray spectroscopy

• We identified three different mode of oil migration.
• Liquid oil droplets appeared on the surface of the chocolate with silicone oil migration.
• Chocolate fat bloom caused by fat migration was enhanced by silicone oil migration.

We have developed a novel method to observe oil migration in chocolate using scanning electron microscopy and energy dispersive X-ray spectroscopy (EDX). If silicone oil is used as the mobile phase in migration, the amount of migrated silicone oil can be evaluated using the EDX signal. Compound chocolate placed on the silicone-oiled cotton resulted in the appearance of liquid oil droplets on the surface of the chocolate within 10 days at 24 °C. Fat blooming was also induced by these oil droplets at 2.5 months. The amount of silicone oil that migrated into the chocolate was evaluated based on the weight change of the chocolate and the EDX signal from the silicone oil. Quantitative analysis indicated that two independent migration mechanisms, diffusion and capillary force, induced migration. In addition, the EDX signal indicated superfast migration from a spot that was distinct from the area of diffusion or capillary force migration. The EDX signals from phosphorus or magnesium atoms were helpful in identifying cacao particles in chocolate since these elements were specific to the particles in chocolate. Homogeneous distribution of silicone oil was observed around the particles in chocolate, thus, these particles might not help to produce a specific migration pathway in chocolate.

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