Abstract
An overview is provided of the status of research at the frontiers of investigation of the chemistry and photochemistry of two classes of natural plant pigments, the anthocyanins and the betalains, as well as of the pyranoanthocyanin pigments formed from anthocyanins during the maturation of red wine. Together, anthocyanins and betalains are responsible for almost all of the red, purple and blue colors of fruits and flowers and anthocyanins and pyranoanthocyanins are major contributors to the color of red wines. All three types of pigments are cationic below about pH 3, highly colored, non-toxic, reasonably soluble in water or alcohol and fairly stable to light. They exhibit good antioxidant or antiradical activity and, as part of our diet, confer a number of important health benefits. Systematic studies of model compounds containing the basic chromophoric groups of these three types of pigments are providing a deeper understanding of the often complex chemistry and photochemistry of these pigments and their relationship to the roles in vivo of these pigments in plants. These natural pigments are currently being exploited as starting materials for the preparation of novel semi-synthetic dyes, pigments and fluorescence probes.
Highlights
The colors of fruits and flowers, ranging across the visible spectrum from white to yellow to orange, red, purple or blue (Stournaras et al 2013), are an integral part of the beauty of nature that we as humans perceive with our limited trichromic vision (Cronin et al 2014, Marshall and Arikawa 2014)
Among the natural pigments of fruits and flowers, the anthocyanins and the betalains are noteworthy from the perspective of the range of colors that they are capable of producing in nature as the result of changes in their chemistry
Since they have been consumed in food for millennia, both are generally regarded to be non-toxic and are available for use as natural food colorants in the form of crude extracts from either grape residues from red wine production in the case of anthocyanins or from red beetroot in the case of betalains
Summary
The colors of fruits and flowers, ranging across the visible spectrum from white to yellow to orange, red, purple or blue (Stournaras et al 2013), are an integral part of the beauty of nature that we as humans perceive with our limited trichromic (red, green, blue) vision (Cronin et al 2014, Marshall and Arikawa 2014). Despite their very distinct chemical structures, both anthocyanins and betalains are cationic below about pH 3, water- and alcohol-soluble, highly colored (Shimamoto and Rossi 2015), and reasonably stable to light, though their slow fading or photobleaching in sunlight is the basis of the Anthotype photographic process (Herschel 1842, Fabbri 2012, Coelho 2013) Since they have been consumed in food for millennia, both are generally regarded to be non-toxic and are available for use as natural food colorants in the form of crude extracts from either grape residues from red wine production in the case of anthocyanins or from red beetroot in the case of betalains. These studies have been useful for the elucidation of the relationship between the complex chemistry and photochemistry of these pigments and their biological roles in plants and for the rational design of novel semi-synthetic dyes, pigments and fluorescence probes
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