Author details: Pr. Olivier DANGLES studied chemistry at the Ecole Normale Supérieure of Cachan, France (1981-1985) and got a PhD of organic chemistry at the Paris - Orsay University (1989). An assistant professor at Strasbourg University (1989-1992), then a researcher at the National Center of Scientific Research (CNRS, 1992-1995), he devoted his research to the chemistry of anthocyanins (plant pigments). In 1995, he was appointed a professor of chemistry at Lyon-I University. Since 2000, he is a professor of chemistry at Avignon University and works in a joint research unit (website: https://www6.paca.inrae.fr/sqpov) with the National Institute for Research in Agriculture, Food & Environment (INRAE). His main research topics deal with the chemistry of polyphenols and carotenoids in relation to their coloring properties and their effects on human health. In 2014 he was awarded the scientific prize of Groupe Polyphenols on the occasion of the 26^th International Conference on Polyphenols in Nagoya. He is among the main authors of more than 100 publications (h-index = 43).

Fields of Expertise: chemistry of polyphenols and carotenoids, physical chemistry of anthocyanins (structural transformations, metal binding, copigmentation), chemical modeling of the antioxidant properties of polyphenols and carotenoids in the digestive tract, synthesis of polyphenols and their human metabolites, synthesis of anthocyanins and analogs.

Abstract: Anthocyanins are polyphenolic O-glycosides widely responsible for the bright red, purple and blue colors in the plant kingdom, including a great variety of fruits and vegetables. As such, they have attracted considerable scientific and industrial interest as potential natural food colorings. However, individual anthocyanins are intrinsically reactive molecules combining electrophilic, nucleophilic and electron-donating properties. This reactivity may be a source of color diversity with, for instance, the formation of new pigments upon winemaking and storage, but also a cause of great color instability involving a combination of reversible and irreversible mechanisms (e.g., water addition, autoxidation) leading to colorless products. Hence, using anthocyanin-rich plant extracts as food colorants requires a deep understanding of these color-damaging mechanisms and, no less importantly, of the color-stabilizing mechanisms developed by plants, including -stacking interactions (self-association, copigmentation), metal binding and a combination of both. The potential of anthocyanins from deeply colored vegetables, typically acylated by hydroxycinnamic acid residues, will be emphasized in that respect. Moreover, food-grade biopolymers (proteins, polysaccharides) may provide suitable matrices for ready-to-use formulations of anthocyanins as food colorings. Overall, the mechanisms of color loss and color stabilization will be discussed as a function of anthocyanin structure and environment, and some challenges still ahead will be outlined