Ouissam Abbas

The chemical and physical properties of imidazolium-based ionic liquids are determined by the interactions between the counter-ions. The C(2) position plays an important role in these interactions, as it represents the predominant site for interionic hydrogen bonding. This study shows that the directional hydrogen bonds between highly symmetrical anions (iodide, tetrafluoroborate, hexafluorophosphate) and the C(2)-H group of the 1-methyl-3-propylimidazolium cation determine the molecular and macroscopic behavior in terms of the thermal properties. Upon replacing the C(2) proton by a methyl group, the anion repositions itself at the C(4)/(5) moiety, where it forms a new hydrogen bond, apparently with only one of the two CH groups. In addition, the larger the anion is in diameter, the more likely it will establish further interactions with other parts of the cation, such as the propyl chain.

Currently, many methods based on various analytical techniques are used to authenticate agro-food products. Among them, vibrational spectroscopy techniques include NIR, MIR, Raman and Terahertz techniques. They are techniques to consider when authenticity controls need to be established at the field level, at the point where products are delivered to factories or during the production process. Methods based on these techniques are indirect, rapid and do not require skilled staff. They are not confirmatory and are therefore seldom used in official control processes. A section of this chapter provides a general overview of the technology, main principles, instrumentation, sample presentation and new trends, as well as giving a brief overview of the chemometric tools used to extract chemically relevant information from the spectra. In another section of the chapter, several examples are discussed to illustrate the potential of vibrational spectroscopy in tackling authenticity challenges (e.g., the discrimination of cereal varieties), in identifying botanical origin, geographical origin and distillers’ dried grains and solubles (DDGS) production process, in the traceability and authentication of fruits and in the early detection of fraud in food/feed ingredients.

Description of the subject. Phenolic compounds (PCs) are the most abundant secondary metabolites in plants. This work was part of a study that sought to develop rapid screening FT-Raman methods for identifying and quantifying classes and/or types of PCs in the dry extracts of plant products. Objectives. Fourier transform Raman spectroscopy (FT-Raman) coupled with chemometric tools was used to characterize and discriminate four families of phenolic compounds: two important classes of phenolic acids, hydroxybenzoic and hydroxycinnamic acids, as well as their derivatives and flavonoids. Method. For this study, 25 standards of phenolic compounds were used (47 standards in total, taking account of the different brands). Repeatability and reproducibility studies were conducted to verify the Raman assignments of gallic acid. Raman characterization with the most significant spectral bands of phenolic compounds was done using spectra ranging from 1,800 to 50 cm-1. A Fisher test was applied to pre-processed Raman spectra (SNV) and 20 Raman scattering signals were used to differentiate each class of phenolic compounds. Results. Hydroxybenzoic acids, hydroxycinnamic acids, their derivatives and flavonoids have been characterized by Raman spectroscopy; bands have been identified and differentiated within and between groups. Conclusions. The scattering intensities located around 1,600-1,699, 1,300-1,400 and below 200 cm-1 were responsible for differentiating 100% of phenolic compound families, classes and subclasses.