**5. Chemical composition**

Polyphenols (**Figure 3**) are the secondary metabolites found mostly in both fruit and by-products. Many factors may alter the contents of polyphenols, as well as other biocompounds in a plant species, such as the area under cultivation, the maturation time, climatic conditions during the cultivation stage, the season of the harvest year, and the storage of the crop raw material. In addition, the seeds of CA, CP, PX, and TM during their processing go through a heating step, and the temperature used can contribute negatively in reducing the levels of the assets [37]. They are derived from phenylpropanoids, where their main representatives are phenols, lignins, and flavonoids [6].

Flavonoids are low molecular weight compounds and are derived from benzog-pyrone, are responsible for the pigmentation of flowers, and protect against damage caused by light, fungi, or parasites. They have a chemical structure consisting of 15 carbon atoms, characterized by the presence of a diphenylpropan (C6-C3-C6) attached to two benzene rings (A and B), and depending on the oxidation of the pyran ring, the ring A is derived from the acetate/malonate route, and ring B is derived from phenylalanine, and its name is variable according to ring C [6].

#### **Figure 3.**

*Polyphenol structural formula: A) gallic acid; B) (+)-catechin; C) (−)-epicatechin; D) (−)-epigallocatechin; E) vanillic acid; F) protocatechuic acid; G) caffeic acid; H)* p-*coumaric acid (adapted from Alves [32]).*
