Mid-infrared Spectroscopy as a Probe for Caramelization in Dispersed Systems

This work explores the use of mid-infrared with attenuated total reflectance (ATRIR) for optimization of caramelization. Systems of incrementally increasing complexity were studied from simple sugar solutions to complex dispersed systems. During caramelization of simple sucrose solutions, there were ATRIR spectral changes across the temperature range of 140 to 220 °C and principal component analysis (PCA) provided a clear discriminating function across this temperature range with a large change in PC1 from 190 to 210 °C which spans an insufficiently caramelized sample and an over caramelized sample. Spectra from systems with a dispersed lipid contained an additional source of variance because the dispersed phase size (≈ 10–100 μm) exceeds the IR path length of ≈ 1 μm. Therefore, the proportion of lipid and water/carbohydrate probed by the ATRIR depends upon the arbitrary arrangement of lipid droplet in relation to the ATRIR beam. The PCA had parallel lines approximately perpendicular to the y = x line. The distance along the y = x line was indicative of the degree of caramelization and the distance from the y = x line depended on the ratio of ν(O–H) and ν(C–H) stretching band areas. Following band height normalization of the 900–1200 cm −1 spectral region, the result of PCA was very similar to that for the sugar-only system with little variance due to the proportion of lipid sampled in a particular spectrum. Therefore, ATRIR can be used to optimize caramelization even for the complex dispersed phase caramel systems.