Non-enzymatic browning of wine induced by monomeric flavan-3-ols: A review.

• Non-enzymatic browning widely occurs in wine during and after vinification. • Mechanisms of non-enzymatic browning induced by monomeric flavan-3-ols are reviewed. • Chromatic features and contribution of various xanthylium derivatives are discussed. • Factors that influence non-enzymatic browning in wine are summarized. • Insights into the complete reaction pathways of non-enzymatic browning are still lacking. Non-enzymatic browning occurs widely in both white and red wines, and it has a huge impact on the color evolution and aging potential. Previous studies have proved that phenolic compounds, especially those with catechol groups, are the most important substrates involved in browning reactions of wine. This review focus on the current knowledge of non-enzymatic browning in wine resulting from monomeric flavan-3-ols. First, some relevant aspects of monomeric flavan-3-ols are introduced, including their structures, origins, chemical reactivities, as well as potential impacts on the organoleptic properties of wine. Second, the mechanism for non-enzymatic browning induced by monomeric flavan-3-ols is discussed, with an emphasis on the formation of yellow xanthylium derivatives, followed by their spectral properties and effects on the color change of wine. Finally, attentions are also be given to the factors that influence non-enzymatic browning, such as metal ions, light exposure, additives in winemaking, etc. [ABSTRACT FROM AUTHOR]