## 3 Phenolic Compounds of Sweet Cherry By-Products
### Non-Flavoroids  
Phenolic acids are abundant in red fruits and belong to a non-flavonoid group [42; 45]. They can be divided into hydroxybenzoic (C\({}_{6}\)-C\({}_{1}\)) and hydroxycinnamic (C\({}_{6}\)-C\({}_{3}\)) acids (Figure 2) [1; 42]. Hydroxybenzoic acids are aromatic compounds composed of simple phenols, including gallic, p-hydroxybenzoic, protocatechuic, vanillic, and syringe acids. In plants, hydroxybenzoicics occur mostly in the glycoside form [1]. On the other hand, hydroxycinnamic acids are phenolic acids with a three-carbon side chain. Chlorogenic, caffe, ferulic, p-comamic, and sinapic acids are examples of hydroxycinnamics [1]. Both the by-products and fruits of _P. avium_ contain a minor amount of hydroxybenzoic acids. In by-products, the hydroxybenzoic acid derivative and protocatechuic acid aglycone were the only hydroxybenzoics detected [7; 10]. In the hydroethanolic extract and the aqueous infusion of cherry stems, the hydroxybenzoic acid derivative content was 299.3 \(\pm\) 6.4 and 918.4 \(\pm\) 31.2 \(\upmu\)g/g dw, respectively [7] (Table 3). There are no reports about the presence of this type of phenolic acid in cherry leaves and flowers. Regarding the sweet cherry fruit, two hydroxybenzoics have been reported, such as a protocatechuic acid derivative and a protocatechuic acid-glycoside [18]. The first compound was identified for the first time in this study and presented higher amounts  
Figure 2: Chemical structure of main phenolic acids (hydroxybenzoic and hydroxycinnamic acids) found in _Prunus avium_ L.  
(1538.92 ug/g dw) in the Satin cultivar of _P. avium_[18] (Table 3). The same research team obtained similar results in previous work with Portuguese sweet cherries [6]. Other hydroxybenzoic acids such as gallic, p-hydroxybenzoic, and 2,5-dihydroxybenzoic acids have also been found in cherries [1]. Hydroxycinnamic acids are products of the phenylpropanol pathway possessing the basic structure of trans-phenyl-3-propenoic acid, with one or more hydroxyl groups attached to the phenyl moiety. They may have a trans or cis configuration and are ubiquitous in the plant kingdom. Many studies have reported that hydroxycinnamics are the class of phenolics present in significant amounts in cherries and their by-products [7; 12; 18; 44]. Phytochemical studies have showed that hydroxycinnamic acids are the main compounds present in _P. avium_ by-products. A study conducted by [PERSON] et al. [12] found p-coumaric acid hexoside, p-coumaroylquinic acid, and 3-O-caffeoylquinic acid in hydromethanonic extracts, infusions, and decosections of _P. avium_ stems (Table 3). Moreover, ferulic acid hexoside and sinapic acid were also quantified in considerable amounts [12]. Caffeoylquinic acid-glycoside, cis-3-O-caffeoylquinic acid, and trans-5-caffeoylquinic acid were other hydroxycinnamic acids reported in cherry stems [10]. Similarly, other studies quantified hydroxycinnamic acids at a total of 3506.9 and 3484.0 ug/g dw in hydroethanonic extracts and aqueous infusions of stems, respectively [7]. These values correspond to ca. 9.4% and 13.2% of total phenolic compounds [7]. Regarding _P. avium_ leaves, this type of phenolic acid is present at a total of 34,858.1 and 43,882.7 ug/g dw, representing 75.3% and 63.7% of total phenolics quantified in the aqueous infusion and hydroethanonic extract, respectively [7]. Data from the literature show that 5-O-caffeoylquinic acid was the major compound found in extracts of cherry leaves, followed by 3-O-caffeoylquinic acid [7; 10]. Hydroxycinnamic acid derivatives, p-coumaric, dicaffeoylquinic, and p-coumaroylquinic acids were also detected in _P. avium_ leaves (Table 3) [7; 10]. [PERSON] et al. [13] reported the presence of caffeic, chlorogenic, and p-coumaric acids in cherry leaves at higher amounts than those found in fruits. Moreover, ferulic acid was identified for the first time in this study, while chlorogenic acid was the predominant hydroxycinnamic acid found just in cherry [13]. In _P. avium_ flowers, [PERSON] et al.