# Anthocyanins, Phenolic Compounds, and Antioxidants from Extractions of Six _Eucalyptus_ Species
## 1 Introduction  
_Eucalyptus_ is a genus of over 900 species and subspecies of flowering trees and shrubs found in the Myrtaceae family [1]. Originally from Australia, nowadays _Eucalyptus_ can be found all over the world [2], and with 18 million ha planted in over 90 countries, it is one of the most widely scattered hardwoods worldwide [3]. _Eucalyptus_ spp. are fast growing plants with the capacity to tolerate harsh environments such as wild fires, drought, and soil acidity [4]. Because of this, numerous species of _Eucalyptus_ are used in the wood industry for the production of pulp, timber, and paper [5], while the bark, leaves, and branches are usually considered by-products utilised for energy production [6, 7]. Even the production of pellets using mixtures of microalgae and _Eucalyptus_ has been studied, reducing the negative impact on ecosystems and reducing waste. In Galicia, in north-western Spain, the first specimen planted was _Eucalyptus_, in 1850. Nowadays, the numbers of species of genus _Eucalyptus_ found in Galicia include 40 taxa (37 species and 3 subspecies), including several hybrids [8]. A study by Picos [9] showed that in Galicia, in 2017, 8.5 million of m\({}^{3}\) of wood had been cut, which represented 47% of the total wood cut in Spain, and accounted for 1.9% of the round-wood production in the European Union. Fifty per cent of the total wood cut was eucalyptus. The forest industry in Galicia employed 20,320 people in 2017 and had a turnover of 2200 million euros [9, 10]. In addition to its use to obtain paper pulp, other uses have been analysed that highlight its potential in other industries. The medicinal properties of _Eucalyptus_ spp. have been reported in various studies [2] and high amounts of polyphenols are known to be found in _Eucalyptus_[4,11]. Polypphenols are complex bioactive molecules found naturally in trees and plant-based foods such as berries, cocoa, tea, and coffee [12,13]. Polypphenols can be divided into flavonoids, phenolic acids, stilbenes, and lignans [14]. Research on the characteristics and properties of polyphenols have linked these molecules to the prevention of cancer, diabetes, osteoporosis, coronary disease, neurodegenerative diseases, and diabetes mellitus [15]. _Eucalyptus_ leaves are being widely studied as they contain volatile essential oil, with multiple widespread biological activities such as antimicrobial, antispeptic, antioxidant, and antifungal [16,17]. The leaves are evergreen, simple, hairless, and with a smooth margin, in other words without teeth or serrations. They usually have two types of leaves: those of the young specimens are wide and often lack stalks, while those of the adult specimens are more elongated, alternate, and always have an obvious stalk. The leaves can be classified according to the venation and the shape. The adult sheet has a central nerve and pinnate sides that are usually welded on a line next to the margin. According to the venation, they can be classified into almost parallel, oblique, and transverse, and according to shape, they can be classified into lancelate, broadly lancelate, narrowly lancelate, elliptic, ovate, linear, and oblique [8]. _Eucalyptus_ leaves are a great source of antioxidants, particularly flavonoids, which offer protection against from oxidative stress and free radical damage. The flavonoid subgroups are flavones, flavonoids, flavanones, flavanonols, flavanonols or catechins, anthocyanins, and chalcones [18]. The main flavonoids presented in eucalyptus are catechins, isonhamentin, luteolin, kaempfer, phloem, and quercetin [19]. On the other hand, _Eucalyptus_ leaf extract can also be used to impart new functionality to textile fibres, such as the production of anti-UV and antimicrobial cotton fabrics through dyeing, thus improving cotton material [20]. This application works to mitigate the appearance of cyanotoxins in the water, toxic metabolites [21], ensuring the optimal state of water security.