Probing temperature able to improve Raman spectroscopic discrimination of adulterated olive oils

Abstract

An effective method for improving Raman spectroscopic identification of adulterated extra virgin olive oil (EVOO) was proposed. It was based on probing an optimal sample temperature where the spectral differentiation among components was enhanced, since temperature-induced spectral variations of individual components expected to be diversely different depends on their molecular structures. Initially, oleic and linoleic acids were separately frozen, and Raman spectra were consecutively collected at regular intervals as the temperature increased. The spectral variations of oleic and linoleic acids were dissimilar with each other due the difference in their molecular structures. In the temperature-varied spectra of pure EVOOs and adulterated EVOOs, both the magnitudes and patterns of the spectral differences between the two groups differed, and the measurement at -36.4 degrees C resulted in the lowest discrimination error of 8.0% based on linear discriminant analysis using principal component scores. The spectral features of the two groups became more discernible at this temperature due to the dissimilar temperature-dependent molecular vibrations of the components, which improved the authentication accuracy.