Comparative studies on molecular compositions of different varieties of chocolates using DFT-based vibrational analysis and ATR-FTIR spectroscopy coupled with bootstrap assisted PCA

Chocolate is one of the most popular widely consumed food products (Tan et al. in Nutrients 13(9):2909, 2021. https://doi.org/10.3390/nu13092909) and comprises of various bioactive compounds including proteins, carbohydrates, fats, and antioxidants. In this study, attenuated total reflectance fourier transform infrared spectroscopy (ATR-FTIR spectroscopy) was employed for a preliminary investigation of the molecular composition and authenticity comparison of four commercially available different varieties of chocolate samples from the Indian market, namely Barone, Dairy Milk, Munch, and Nestlé. Experimental FTIR spectra were compared with theoretical vibrational spectra obtained from density functional theory (DFT) calculations at the B3LYP/6-311++G(d, p) level for major constituents, particularly theobromine and caffeine, showing good agreement between calculated and observed vibrational frequencies. Mulliken charge analysis and molecular electrostatic potential (MEP) mapping revealed electron-rich regions localized around oxygen and nitrogen atoms, while positive potential regions were observed near hydrogen atoms, consistent with the spectral assignments. Furthermore, bootstrap-assisted principal component analysis (PCA) was applied to the FTIR data and successfully discriminated four chocolate samples, demonstrating the reproducibility and reliability of the dataset. The combined application of ATR-FTIR spectroscopy, DFT calculations, and multivariate statistical analysis thus provides a robust and effective approach for chocolate profiling and authenticity verification.