Abstract
Catechins belonging to polyhydroxylated polyphenols are the primary compounds found in green tea. They are associated with many physiological properties. Epicatechin (EC) is a non-gallate-type catechin with four phenolic hydroxyl groups attached. The changes in EC treated with color light illumination in an alkaline condition were investigated by chromatographic and mass analyses in this study. In particular, the superoxide anion radical (O2•−) was investigated during the EC photolytic process. EC is unstable under blue light illumination in an alkaline solution. When EC was treated with blue light illumination in an alkaline solution, O2•− was found to occur via a photosensitive redox reaction. In addition, the generation of monomeric, dimeric, and trimeric compounds is investigated. On the other hand, epigallocatechin gallate (EGCG), which is a gallate-type catechin, is stable under blue light illumination in an alkaline solution. Adding EGCG, during the blue light illumination treatment of EC decreased photolytic formation, suggesting that gallate-type catechins can suppress the photosensitive oxidation of EC. Gallate-type catechins are formed via the esterification of non-gallate-type catechins and gallic acid (GA). The carbonyl group on the gallate moiety of gallate-type catechins appears to exhibit its effect on the stability against the photosensitive oxidation caused by blue light illumination.
Highlights
IntroductionPolyphenols are polyhydroxylated compounds and secondary metabolites in plant products
Polyphenols are polyhydroxylated compounds and secondary metabolites in plant products.These phenolic compounds have one or more hydroxyl groups attached to an aromatic ring and the structure may consist of a simple phenolic compound to a complex polymer [1]
According to the gallic acid (GA) ester at the C3 position of the catechins, two major catechin types comprise about 80% of the polyphenolic compounds found in green tea: non-gallate-type catechins, such as epicatechin (EC) and catechin; gallate-type catechins, such as epicatechin gallate (ECG) and Molecules 2019, 24, 787; doi:10.3390/molecules24040787
Summary
Polyphenols are polyhydroxylated compounds and secondary metabolites in plant products. These phenolic compounds have one or more hydroxyl groups attached to an aromatic ring and the structure may consist of a simple phenolic compound to a complex polymer [1]. According to the gallic acid (GA) ester at the C3 position of the catechins, two major catechin types comprise about 80% of the polyphenolic compounds found in green tea: non-gallate-type catechins, such as epicatechin (EC) and catechin; gallate-type catechins, such as epicatechin gallate (ECG) and Molecules 2019, 24, 787; doi:10.3390/molecules24040787 www.mdpi.com/journal/molecules. Molecules 2019, 24 epigallocatechin gallate (EGCG) [3]. The structures of EC, EGCG, pyrogallol (PG), and GA are shown (ECG) and epigallocatechin gallate (EGCG) [3].
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