## 1 Introduction
In recent years, more and more studies have been frequently published looking at red berries' composition and antioxidant properties. Several methods have been adapted to determine antioxidants in plants, foods, dietary supplements, and food supplements. The total antioxidant capacity of food does not necessarily correlate with the value obtained by summing the levels of individual antioxidants from a composite food matrix. Antioxidant  
Figure 1: The main unconventional applications of blackberries in the food industry. activity can be monitored by various assays with different mechanisms, including hydrogen atom transfer (HAT), single electron transfer (SET), reducing power, and metal chelation. Among the methods using the SET reaction mechanism, the FRAP (Ferric reducing antioxidant power), the Folin-Ciocalteu method, and the DPPH (2,2-diphenylpicrylhydrazyl) radical scavenging method are widely used. Flavonoids and anthocyanins can also be quantified by UV-Vis spectrophotometry. In parallel, extensive research is taking place worldwide to find the optimal extraction methods to obtain antioxidant-rich products for a range of berries. Although conventional solvent extraction is the most widespread technique for extracting antioxidant compounds from red berries, new non-conventional methods have emerged as environmentally friendly alternatives to the first method, such as ultrasound, microwave, and pressure-assisted extractions, applied alone or in conjunction with the use of solvents, to reduce energy and solvent requirements [16; 17]. The traditional method for anthocyanins extraction is Soxhlet extraction with acidified ethanol or methanol. Acid addition is necessary because anthocyanins are reactive compounds and are sensitive to pH changes. Anthocyanins present instability and tend to change their color in response to changes in environmental parameters such as pH, heat, light, oxygen, and co-existing substances [18]. Anthocyanins can be found in different chemical forms that depend on the solution's pH (Figure 2). The presence of ascorbic acid in an environment containing anthocyanins causes a loss of color, thus suggesting a direct interaction between the two molecules. At the same time, the presence of oxygen in the environment will favor faster degradation of anthocyanins by ascorbic acid, thus determining the formation of the polymeric pigment and the whitening of the anthocyanin pigment. The specific degradation process is unknown; however, adding ascorbic acid to anthocyanins increases the decomposition rate of both molecules. The presumed mechanisms by which this phenomenon would occur are the direct condensation of ascorbic acid with anthocyanins or the formation of hydrogen peroxide and oxidative cleavage [19]. Figure 2: The structures of cyanidin-3-\(O\)-glucoside at different pHs. The most commonly used extraction solvents are acidified methanol and ethanol, but in the food industry, ethanol is preferred because of the toxicity of methanol. Among ethanol and methanol extractions, many other extraction solvents have been mentioned in the literature, such as: ethyl acetate, chloroform, acetone/water 10-90% (\(v\)/\(v\)), n-hexane, isooctane [20]. Solvents with high polarity (ethanol and methanol) are favorable for use in the extraction of polar compounds such as phenolic compounds and flavonoids. Non-polar solvents, such as ether, or solvents with low polarity, such as chloroform and ester, are used in specific cases with a low frequency of use. In addition to the extraction method and solvent selection, one should pay great attention to the extraction temperature and pH. Different extraction temperatures may affect the types of polyphenols extracted. At high extraction temperatures, the formation of new compounds, known as products of the Maillard reaction, also involves the polyphenols extraction, and thermal degradation of the polyphenols may occur [21]. A solvent mixture can display more affinity with the chemical target than a pure solvent and can enhance the extraction yields.