# _Vaccinium_ Species (Ericaceae): From Chemical Composition to Bio-Functional Activities
## 4 The Chemical Profile of _Vaccinium_ Leaves  
A body of scientific research studies proved the contribution of berries' consumption to the main targets of functional foods, such as health maintenance and reduced risk of some chronic diseases. However, in addition to fruits, the leaves of the _Vaccinium_ species have also been used in traditional remedies (Table 1). Leaves are considered to be by-products of berries' cultivation. Their traditional use against several diseases, such as inflammation, diabetes, and ocular dysfunction, has been almost forgotten in recent times. The scientific interest regarding the leaves' composition and beneficial properties has grown, demonstrating that leaves may be considered to be an alternative source of bioactive compounds. Analytical studies reveal that the chemical  
Figure 4: The chemical structures of the main iridoids isolated from _Vaccinium_ species [64, 65]. composition of leaves is similar to that of the fruits or even higher, indicating that they may be used as an alternative source of bioactive compounds for the development of functional foods, nutraceuticalids, and/or food supplements. [PERSON] et al. [74] showed that red leaves of _Vaccinium_ genus contain anthocyanins, which are absent in green leaves. Both green and red leaves contain proanthocyanidins, especially procyanidin. [PERSON] and [PERSON] [75] analysed the phytochemical composition of fruits and leaves of several _Vaccinium_ species; among them, _V. myrtillus_ leaves were the first source of phenolic compounds, followed by _V. oxycocos_ leaves. The major polyphenic group was proanthocyanidins, followed by flavonoids. Proanthocyanidins, flavan-3-ols, phenolic acids and flavonoids were in higher concentration than the respective fruits [76]. Proanthocyanidins were detected in small quantities in the leaves of _V. viitis-idaea_[41]. [PERSON] et al. [76; 77] have detected proanthocyanidin B1/B2 and cinchonin in the leaves of _V. corymbosum_. In the same year, [PERSON] et al. [78] identified the presence of cyanidin 3-O-glucoside, cyanidin 3-O-glucuron, and cyanidin 3-O-arabinoside in the methanolic leaf extract of _V. corymbosum_, confirming that _V. corymbosum_ leaves possess a higher total anthocyanins content compared to _V. virgatum_ and _V. formosum_ leaves. After proanthocyanidins, flavonoids are the most important classes of constituents of _Vaccinium_ leaves. Quercetin-3-O-glucuron is the most abundant flavonoid (70-93% of total flavonoids) [79]. Other identified flavonoids in the leaves are quercetin-3-O-galactosidase, quercetin-3-O-(4\"-3-hydroxy-3-methylglutaroyl)-\(\alpha\)-rhammoside, quercetin-3-O-arabinoside, quercetin-3-O-glucose, quercetin-3-O-glucose, quercetin, as well as three kaempfer glycosides [41; 79]. In addition, [PERSON] et al. [41] have detected several other bioactive compounds in the leaves, such as flavan-3-ols, six different isomers of cinchonin, three proanthocyanidins, and two coumaroyl iridoids. [PERSON] et al. [80] investigated the flavonoids present in _V. myrtillus_, and found flavonoid C-glycosides and _O_-derivatives of apigenin and luteolin; the main ones are apigenin-7-glucuron, vitexin-2-O-rhammoside, and isorientin. Flavonoid glycosides are represented mainly in quercetin derivatives, particularly rutin and quercetin-3-glucose-7-rhammoside. Isorhamentin-3-glucose and kaempfer-3-glucuron were also found in the extract. Additionally, free aglycones were also present (myricetin, quercetin, luteolin and kaempfer). The main flavonoids detected in the _V. oxycocos_ leaves were hyperoside and quercetin-3-O-rhammoside, together with quercetin-3-O-xyloside, quercetin-3-O-arabinoside and procyanidin A2 [66]. The green leaves of _V. viitis-idaea_ have similar phytochemical profiles to those of _V. myrtillus_[41; 79]. [PERSON] et al. [79] and [PERSON] et al. [41] have quantified the phenolic compounds in methanolic and hydroalcoholic leaf extracts of _V. viitis-idaea_. In general, hydroxycinnamic acids and flavonoids were the most abundant compounds.