Anthocyanins and betalains play important roles both in plant physiology, visual attraction for pollinators and seed dispersers, but also in food mainly defining its aesthetic value. Since anthocyanin and betalain structures allow to predict only part of their appearance, additional chemical and anatomical functions are required to modulate the appearance of plants and coloured food. Physiological effects that the same pigments exert in plants are supposedly similar to those which they show in humans following ingestion of coloured food. Therefore, anthocyanins and betalains both in fresh and also processed fruit and vegetables serve two functions: They improve the overall appearance, but also contribute to consumers' health and well-being.

Functional properties of anthocyanins and betalains in plants, food, and in human nutrition

Anthocyanins occur widely in plants, being responsible for their blue, purple, violet, magenta, red and orange coloration; while betalains, consisting of red-violet betacyanins and yellow-orange betaxanthins, occur exclusively in families of the order Caryophyllales. The occurrence of these two classes of pigments is mutually exclusive. Their stability is markedly influenced by environmental and processing factors such as pH, temperature, O2, enzymes and condensation reactions. Due to their inherent instability these pigments, and betalains in particular, have not been widely used as food colorants. However, structural variants of the anthocyanins, i.e. polyacylated and copigmented species, have demonstrated remarkable stability and have great potential for use as stable natural colorants. Anthocyanin and betalain preparations can be used to colour a variety of foods and pharmaceuticals with compatible physicochemical properties, yielding highly coloured and high quality products. Their application could be enhanced, however, with new sources and stable structural variants, modification of current processes and foods, and technological advances (e.g. industry-scale extractions/purifications, microbial purifications, biotechnology) that would make purer and more stable preparations available. In this chapter the chemistry and biochemistry of anthocyanins and betalains—their structure and distribution, functions, biosynthesis, factors influencing their stability, methods of extraction and analysis, and current and potential sources and uses—are reviewed.

Anthocyanins and betalains

Alkaloids from Portulaca oleracea L.

Oxidative cyclizations are important transformations that occur widely during natural product biosynthesis. The transformations from acyclic precursors to cyclized products can afford morphed scaffolds, structural rigidity, and biological activities. Some of the most dramatic structural alterations in natural product biosynthesis occur through oxidative cyclization. In this Review, we examine the different strategies used by nature to create new intra(inter)molecular bonds via redox chemistry. This Review will cover both oxidation- and reduction-enabled cyclization mechanisms, with an emphasis on the former. Radical cyclizations catalyzed by P450, nonheme iron, α-KG-dependent oxygenases, and radical SAM enzymes are discussed to illustrate the use of molecular oxygen and S-adenosylmethionine to forge new bonds at unactivated sites via one-electron manifolds. Nonradical cyclizations catalyzed by flavin-dependent monooxygenases and NAD(P)H-dependent reductases are covered to show the use of two-electron mani...

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Oxidative Cyclization in Natural Product Biosynthesis

Plant betalains: Chemistry and biochemistry

Betalamic acid, the probable key intermediate in the biogenesis of all betalains, has been detected for the first time as a natural product in numerous species of plants belonging to families of the Order Centrospermae, has been obtained directly from the cleavage of the red beet pigment betanin, and has been characterized by the formation of betanidin when mixed with synthetic cyclodopa, and indicaxanthin on reaction with L-proline.

Linda Kimler

Papers

Betalamic acid, a new naturally occurring pigment

Biogenesis of betalamic acid

The Betalains: Structure, Function, and Biogenesis, and the Plant Order Centrospermae