Polarized FTIR ATR Spectroscopic Study on the Structure of Chocolate: Influence of Mold on Fat Crystalline Structures

Abstract

Control of the fat crystallization process is essential to the quality of chocolate bars. The crystallization proceeds in a mold, which would induce a specific inhomogeneous structure within a chocolate bar. In the structural analysis of the inhomogeneity in chocolate bars, the powder X-ray diffraction method, which is widely used for structural analysis of fats, has a drawback that the sharp diffractions of sugar powder overlap with those of fat components. As a measure to address this issue, the inhomogeneity has been studied by polarized Fourier transform infrared spectroscopy (FTIR) together with the attenuated total reflection (ATR) sampling technique, which can provide a variety of structural information on fat components, such as the conformational regularity, orientation, and packing of hydrocarbon chains and glycerol groups and their position dependence. The infrared spectral features of fat components vary significantly, depending on their position within a chocolate bar, suggesting that there is a clear difference in the conformational and lateral-packing regularity of acyl chains between two surface regions, the mold-side face and the air-side face. The mold-side face exhibits the characteristics of highly ordered acyl chains, whereas the air-side face clearly shows the characteristics of disordered acyl chains. The midpoint between the two faces shows characteristics intermediate between them.