# Elderberry Concentrate Juice Industrial By-Products Characterization and Valorisation
## 1 Introduction  
Elderberry (_Sambucus nigra_ L.) fruit has a dry matter that constitutes 22-29% of its weight, mainly composed of carbohydrates (18%) and anthocyanins (1%) [1; 2; 3; 4]. Elderberries have been widely used throughout history as a folk medicine, mainly due to their anthocyanins, which are potent antioxidant agents and present anticarcinogenic, immuno-stimulating, antibacterial, antialergic and antiviral properties, and, therefore, may contribute to the prevention of several degenerative diseases such as cardiovascular disease, cancer, inflammatory disease and diabetes [4; 5]. Nowadays, elderberry is commercialized in form of dietary supplements [6; 7]. The black-purple-red colour of this berry is due to the presence and concentration of anthocyanins, making it highly demanded as a natural colourant for the food industry [8; 9; 10]. The berry and its juice have been proposed to solve colour losses caused by food processing, as canning [11; 12; 13; 14; 15]. Its addition to wine to improve and emphasize colour, although considered an adulteration and an illegal practice [16], is still a traditional non-commercial practice highly appreciated and valued by local communities. Elderberry fruit is very seasonal (1 month in August in the north of Portugal). The main cultivars are \"Bastardeira\", \"Sabugueeira\" and \"Sabugueiro\", with similar anthocyanins profiles [1]. Only for cyanidin-3,5-diglucoside and cyanidin-3-sambubioside-5-glucosidewere there observed significant differences between the cultivars. The levels of \"Bastardeira\" are higher than those of \"Sabugueiro\". \"Bastardeira\" was reported as the best cultivar concerning total soluble solids, anthocyanins, polyphenols, and antioxidant activity, but containing a lower total free sugar content when compared to \"Sabugueiro\" [1]. Despite these differences, the producers commercialize them as blends. Due to its perishability, it is mostly transformed into juices, stored in a frozen state, or juice concentrate, to allow its storage under refrigeration conditions. The thermally processed juice is a safe alternative to the elderberry fruit consumption due to the presence of sambunigrin, a potentially toxic cyanogenic glycoside. As thermal processing significantly decreases the levels of this compound, it is safer to consume the berries as transformed products rather than fresh [1; 8]. To obtain a concentrated juice, elderberry fruit is firstly destemmed and then mechanically pressed. The resulting must undergoes maceration with enzymes to increase the juice extraction efficiency, enhancing the release of anthocyanins [17]. A new enzymatic clarification/depectinisation followed by ultrafiltration is intended to reduce suspended substances, contributing to a final product with less turbidity. The last step is water evaporation and, afterwards, the obtained concentrate is homogenized and stored. The production process of concentrated juice generates a large amount of by-products (25-40% of the total berry weight) [5; 18]. The pomace, which is composed by the skin and smashed seeds, results from the pressing, while the retenate, which is a sludgy residue, results from the clarification of the juice through the ultrafiltration process [19; 20]. At present, the pomace is used for animal feed, fertilization, or burned, while the retenate is discarded as industrial effluent. The large amount of waste produced in addition to the great loss of valuable compounds also raises serious management problems, both from the economic and environmental point of view [21; 22]. Therefore, there is an urgent necessity for their valorisation. Research on elderberries has been focused on berries and flowers, and on their polyphenol content. In addition, elderberry polysaccharides, namely the xyloglucans, homogalacturons, and rhamnagalacturons, have been reported to have _in vitro_ immunomodulatory activity [6; 7]. Tritergenic acids, namely the involic and olealenoid acids, are the main components in the fruit lipophilic fraction [23].