**2. Natural sources of anthocyanins**

The natural sources of anthocyanins include fruits, flowers, leaves and roots of plants. The most widely consumed anthocyanin natural products include cherries, berries and cereals. Scientific reports reveal several anthocyanins and their derivatives isolated from natural sources. A comprehensive list of some sources with specific anthocyanins is provided in **Table 1**. Anthocyanins occurring in flowers are observed to be more stable than the anthocyanins found in grapes. Studies



#### **Table 1.**

*List of sources of anthocyanins found in flowering plants, fruits and cereals.*

that investigated the chemistry behind intensification and stability of grape wine color upon storage reveal that a cycloaddition reaction leads to the formation of 4-substituted anthocyanins. These anthocyanins are suggested to be the possible reason for stability of wine color upon maturation. The grape varieties that contain 3,5-diglycosides produce wine of an inferior quality compared with the varieties that contain high levels of 3-monoglycosides [45, 46]. The cycloaddition reaction leading to formation of 4-substituted anthocyanins was also observed in seeds of red currant [1]. Cereals form an important part of human diet and they are available in various colors ranging from red, yellow, purple and black. These colored cereals are a rich source of anthocyanins and include common cereals such as wheat, barley, sorghum, rice, maize, rye, oats, etc. [38, 44, 47–50]. Structures of some representative anthocyanins found in cereals, and fruits and flowers are represented in **Figures 1** and **2**, respectively.

**Figure 1.**

*Structures of representative anthocyanins and their derivatives found in cereals.*
