The typical fat used in chocolate is cocoa butter (CB), but cocoa butter substitutes (CBS) is also used because of its availability and functionality. CBS compound chocolate does not require tempering because CBS crystallizes directly in its optimal polymorph, the β’ form. However, CBS crystals can transition from the β’ form to the more stable β form during long-term storage, which can cause fat bloom. Therefore, it is important to understand the behavior of polymorphic transition for CBS.
A previous study showed that the width of X-ray diffraction peaks of CBS changes when CBS is stored at different storage temperatures. This suggests that the strain in CBS crystals changes depending on the storage temperature, which may affect the behavior of polymorphic transition. Therefore, in this study, we focus on the strain in CBS crystals and aim to suppress fat bloom in CBS compound chocolate.
Synchrotron radiation X-ray diffraction (SR-XRD) measurements were performed to estimate the strain in the β’ form for CBS. 100% CBS was used as the sample, and that was melted at 55°C for 1 hour, and stored in incubators at 20°C and 28°C for 3 days. SR-XRD was performed on the prepared samples at BL6A of KEK in Tsukuba, Japan. Reflected-light microscopy was then performed to observe fat blooms. To facilitate the observation of fat blooms, the compound chocolate sample consisting of 95% CBS and 5% CB, to which cocoa powder was added, was used. Samples were prepared as in SR-XRD, and the sample were observed after that were stored for 49 days.
The results of strain calculation from XRD diffraction peaks showed that the strain of β’ form for CBS stored at 20 ºC was larger than that stored at 28 ºC. Thus, the higher storage temperature, the more strain in the crystal decreased. Moreover, observation of the surface of CBS compound chocolate samples stored for 49 days showed that fat bloom was observed in samples stored at lower temperatures. On the other hand, no fat bloom was observed in the samples stored at higher storage temperatures.Thus, the smaller strain of β‘ form, the more fat bloom was suppressed. In this poster, the reduction of the polymorphic transition rate due to the decrease in the strain will be discussed thermodynamically.