Flavonoid Dyes

Flavonoids are water-soluble pigments, which are abundant in vascular plants. They are best known as secondary metabolites and can be found in almost all fruits and vegetables. To date, more than 5000 flavonoids have been detected and hundreds of substances resembling flavones are present in different plants. On the basis of their chemical structure, these pigments are grouped in several classes, the most important of which are listed in Table 6.2. All these compounds involve two benzene rings, linked by a heterocycle. Overall, flavonoids are categorized in accordance with their nature. Typically, flavonoids are not detected by naked eye and are visible only under ultraviolet spectrum but some display a light yellow appearance. Hence, anthocyanins can be tagged as real pigments within the flavonoids as they cover a considerable hue range of colors (Socaciu, 2007). Accordingly, anthocyanins will be discussed in the upcoming section as they have significant impact on the marketing of fruits and vegetables (Havsteen, 2002; Harborne, 2013). Considering the subsets of flavonoids other than anthocya- nins, the catechins, leucoanthocyanidins, and flavonols are highly found in foodstuffs, while flavanone glycosides are normally found in citrus fruits.

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