Dept. of Chemical and Materials Engineering, Univ. of Auckland, Auckland 1142, New Zealand.
J Food Sci. 2018 Apr;83(4):998-1004. doi: 10.1111/1750-3841.14108. Epub 2018 Apr 6.
This study aims to understand the bloom process in untempered chocolate by investigating the polymorphic transformation of cocoa butter and changes in chocolate surface. Cocoa mass with varying particle size distributions (PSD) were used to produce untempered model chocolate. Optical microscopy showed that during 25 d of storage, the chocolate surface gradually became honeycombed in appearance with dark spots surrounded by white sandy bloom areas. In conjunction with X-ray diffraction this indicates that the polymorphic transformation of form IV cocoa butter to more stable form V crystals caused the observed surface changes with the most significant changes occurring within 6 d. As bloom developed the surface whiteness increased, but the PSD of nonfat particles showed limited impact on the changes in whiteness. Moreover, scanning electron microscopy showed separated fat crystals on fat-rich dark spots and empty spaces between particles in bloom areas suggesting redistribution of fat in the chocolate matrix.
The results reported in this work can facilitate the understanding of fat bloom formation in untempered chocolate with respect to the changes in microstructure and surface appearances. It also contributes to show the details of IV-to-V polymorphic transformation in the fat phase as time went by.
本研究旨在通过研究可可脂的多晶型转变和巧克力表面的变化来了解未经调温的巧克力的结块过程。使用具有不同粒度分布（PSD）的可可块生产未经调温的模型巧克力。光学显微镜显示，在 25d 的储存过程中，巧克力表面逐渐呈现蜂窝状外观，深色斑点周围有白色沙质结霜区域。结合 X 射线衍射，这表明 IV 型可可脂向更稳定的 V 型晶体的多晶型转变导致了观察到的表面变化，其中最显著的变化发生在 6d 内。随着结霜的发展，表面变白，但非脂颗粒的 PSD 对变白程度的变化影响有限。此外，扫描电子显微镜显示，在结霜区域的富脂暗斑和颗粒之间的空隙处有分离的脂肪晶体，表明巧克力基质中脂肪的重新分布。
本工作中报告的结果可以促进对未经调温的巧克力中脂肪结霜形成的理解，包括微观结构和表面外观的变化。它还有助于显示脂肪相中 IV 到 V 多晶型转变的细节随着时间的推移而发生。
