Rapid instrumental methods and chemometrics for the determination of pre-crystallization in chocolate

Three rapid instrumental methods for the determination of the pre-crystallization stage in six types of chocolate were studied. The methods were near-infrared (NIR) spectroscopy, fluorescence spectroscopy and tri stimulus colour measurements. The chocolates were tempered into five categories: two levels of under-tempered, two levels of over-tempered and one level of well-tempered chocolate. A temper meter was used as the reference method. NIR and fluorescence data were orthogonalized before modelling in order to remove the chocolate type characteristics. NIR spectroscopy was capable of discriminating between the five tempering groups when the principal component analysis (PCA) model was used on all chocolate types. A partial least squares discriminant analysis on the NIR spectra with the three main tempering groups (over-, well-, and under-tempered) as the dependent variable showed perfect separation of the groups. Using fluorescence spectroscopy it was possible to separate the chocolates into the three main tempering groups in a PCA model, while the colour measurements did not reflect the degree of pre-crystallization.