## 1 Introduction  
Blackberries belong to the thorny shrubs (genus _Rubus_) group and are members of the rose family (_Rosacene_). Wild species are found on five continents, and low-growing shrubs are common in temperate forests and tropical highlands. Some species prefer cool mountain habitats, others grow better in marshy tundra areas. Researchers have identified hundreds of species, but only the fruits of a few species are commercially available [1]. Blackberries (_Rubus fruiticosus_ L.) are widely cultivated edible fruits in Europe and North America. Their composition and nutritional value depend on several agro-geo-climatological factors, such as genotype, environmental conditions, agronomic practices, harvesting time, post-harvest storage, and processing techniques [2; 3]. Among the most important bioactive compounds in blackberries--flavonoids, phenolic acids, tannins, anthocyanins, and vitamins--have been found [4; 5]. The dietary consumption of blackberries has been associated with several health benefits, such as preventing and treating metabolic syndrome, supporting the digestive and immune systems, preventing inflammatory diseases and cardiovascular diseases, and providing protective effects against gastrointestinal cancers [3; 4; 6]. Blackberry presents multiple health benefits for food consumers due to its antioxidant activity and the polypharmacological effects of anthocyanins [7]. Blackberries are used as conventional raw materials in obtaining jam, compete, as well as unfermented and fermented beverages, but they may replace synthetic additives from foodstuffs such as colorants, stabilizers, etc. [8; 9]. Additionally, the use of blackberries improves the nutritional value and shelf life of finished food. The anthocyanins from blackberries can be applied in food packaging systems and as food colorants, since natural dyes are rarely toxic as well as easy to prepare and pollution free [10; 11; 12]. The possible applications are shown in Figure 1.  
During fruit processing, a large by-product quantity is generated with an important bioactive compound content [3; 5; 13]. Through food by-products utilization, it is possible to simultaneously recover the valuable bioactive compounds and minimize the waste quantity. This way, the fruit processing industry has become more environmentally friendly by removing phenolic compounds from the waste, which has a bacteriostatic effect on degradation microorganisms [14]. There are also difficulties in recovering bioactive compounds from food industry by-products. Extractions involve the co-extraction of non-phenolic substances, such as sugars, organic acids, and proteins, which require subsequent purification processes. The temperature decreases solvent viscosity and surface tension, enhancing diffusion and extraction efficiency. However, high temperatures may accelerate the degradation of polyphenols, reduce antioxidant capacity, and produce solvent evaporation. Extraction of polyphenols is usually carried out at low pH, as, in acidic environments, these compounds take a neutral form, which is best suited for solubilization. However, excessive acidification may impair extraction, as the profile of native polyphenols may be distorted by the hydrolysis of simple glycosides. Extraction time is also crucial, as prolonged exposure to oxygen/light can degrade phenols. In addition, other polyphenols are susceptible to oxidation or volatility and therefore require short processes or conditions that protect the dissolved fraction from oxygen/light damage. Current extraction methods (ultrasound-assisted extraction, supercritical fluid extraction, hot-pressurized liquid extraction, microwave-assisted extraction, enzyme-assisted extraction) are generally efficient, sustainable, potentially cost-effective, and easier to scale up. Nevertheless, the optimal feasibility of extracting plant by-products is still far from being within reach. Efforts should be made to find the optimal compromise between maximum recovery and minimum disturbance of polyphenol structure [15].