The use of ATR-FTIR imaging to study coated oil capsules

Fourier transform infrared (FTIR) spectroscopic imaging using a large Internal Reflection Element (IRE), also called Attenuated Total Reflection (ATR) crystal, can be used for the identification and localisation of chemical compounds in solid food products. In this study ATR-FTIR imaging, by means of a large area crystal with a contact diameter of 600 µm with a linear array detector, was used to elucidate the microstructure of the coating of a sophisticated multi-layered oil capsule with active ingredients (sodium ascorbate, sucrose, gelatine, gum, isoflavone). ATR-FTIR imaging with the aid of principal component analysis (PCA) showed the spatial location of the individual ingredients within the layers and that these ingredients are not uniformly distributed within the layers. By ATR-FTIR imaging it was determined that the layer thickness of the soft central coating layer containing lycopene, sodium ascorbate, sucrose and air is about ~156 µm, the 1st sucrose layer ~180 µm and the gelatine/gum ~28 µm. The latter was confirmed by X-ray microtomography (µCT). The other layers could not be identified by µCT.