Food Science Department, University of Guelph, Guelph, ON, Canada.
Food Science Department, University of Guelph, Guelph, ON, Canada; Physics Department, St. Francis Xavier University, Antigonish, NS, Canada.
Food Res Int. 2021 May;143:110224. doi: 10.1016/j.foodres.2021.110224. Epub 2021 Feb 23.
Chocolate is a manufactured product enjoyed worldwide. Over the years, manufacturers have learned how to appeal to humans using this rich-fat food that arouses all the senses. Good quality chocolate is recognized by its smoothness, a slow melt in the mouth, and a snap when bitten, and described as well-tempered. This work compares dark chocolate samples manufactured to obtain under- and well-tempered chocolate, where under-tempered does not show all the physical properties desired by consumers. The microstructure was studied using the ultra small angle X-ray scattering (USAXS) technique, complemented by small and wide angle X-ray scattering to identify the polymorphs. It was observed that under- and well-tempered chocolates exhibited differences in the q-region ~ 2 × 10 Å < q < ~1.5 × 10 Å which correspond to spatial length scales from 32 µm to 3.2 µm. The differences are manifested in the value of the mass fractal dimension, D, obtained when the USAXS data were fitted using the Unified Fit model (Irena software). The characteristic length scale at which these differences were observed falls in length scales detected by humans in the oral cavity. This work proposes that a D = 2.1 characterizes an under-tempered 70% dark chocolate while a D = 2.3 characterizes a well-tempered 70% dark chocolate. This work also presents a simple model that describes the disintegration of those aggregates formed by the basic scatter units for under- and well-tempered chocolate. The model proposes that aggregates formed in under-tempered chocolate persist after the bulk chocolate has melted, which can be perceived as grittiness. However, the model proposes that the aggregates for well-tempered chocolate melt at the same or lower temperatures than the bulk chocolate melting temperature; hence no grittiness is perceived. The model is supported by the observation that the heat of transition for the under-tempered chocolate is smaller than that of the well-tempered case.
巧克力是一种全球范围内受欢迎的加工食品。多年来，制造商们已经学会了如何利用这种能够激发所有感官的高脂肪食品来吸引人类。优质巧克力的特点是口感顺滑、在口中慢慢融化，被咬碎时会发出清脆的声音，并且描述为“调温良好”。这项工作比较了为获得未调温和调温良好的巧克力而制造的黑巧克力样品，其中未调温的巧克力没有表现出消费者所期望的所有物理特性。使用超小角 X 射线散射 (USAXS) 技术研究了微观结构，并结合小角和宽角 X 射线散射来识别多晶型物。观察到，未调温和调温良好的巧克力在 q 区域2×10 Å<q<1.5×10 Å 之间存在差异，这对应于 32 µm 到 3.2 µm 的空间长度尺度。这些差异表现为使用 Irena 软件的统一拟合模型对 USAXS 数据进行拟合时获得的质量分形维数 D 的值。观察到这些差异的特征长度尺度落在人类在口腔中检测到的长度尺度范围内。这项工作提出，D=2.1 可以表征未调温的 70%黑巧克力，而 D=2.3 可以表征调温良好的 70%黑巧克力。这项工作还提出了一个简单的模型，该模型描述了未调温和调温良好的巧克力基本散射单元形成的团聚体的崩解过程。该模型提出，在大块巧克力融化后，未调温巧克力中形成的团聚体仍然存在，这可能会被感知为粗糙感。然而，该模型提出，调温良好的巧克力的团聚体在与大块巧克力的融化温度相同或更低的温度下融化；因此，不会感觉到粗糙感。该模型得到了未调温巧克力的相变热小于调温良好情况的观察结果的支持。
