## 3 Results and Discussion
### Total Anthocyanin, Flavonoid, and Polyphenol Concentrations  
The total anthocyanin, flavonoid, and polyphenol concentrations in the blackberries tested are summarized in Table 1. The results show that the total anthocyanin content ranges from 642.96 \(\pm\) 71.24 to 885 \(\pm\) 59.81 mg cyanidin-3-glucose/100 g DW (average 780.13 \(\pm\) 98.54 mg cyanidin-3-glucose/100 g DW), and the total flavonoid content ranges from 129.75 \(\pm\) 9.5 to 240.93 \(\pm\) 16.95 mg quercetin/100 g DW (average 183.38 \(\pm\) 14.87 mg quercetin/100 g DW). The total polyphenol concentration varies from 2143 \(\pm\) 321.21 to 3311.83 \(\pm\) 54.38 mg gallic acid/100 g DW (average 2872.69 \(\pm\) 231.65 mg gallic acid/100 g DW) depending on the solvent. The values obtained agree with several literature data points [23; 26; 27; 28; 37; 23; 38]; total phenolic compounds present in blackberries could vary based on variety, climatic conditions of the year, soil fertility, harvest time, or extraction method. The Folin-Ciocalteu test for TPC has several advantages, including simplicity, reproducibility, and robustness. However, it has several disadvantages. Firstly, the test is sensitive to pH, temperature, and reaction time, and secondly, overestimation of TPC in the Folin-Ciocalteu test is a serious concern, as reducing sugars and ascorbic acid can be present in high amounts in fruit extracts and can reduce the effect of the Folin-Ciocalteu reagent, which distorts the TPC results. The use of acetonitrile is common in research and analytical measurements, but it is not allowed in industrial-scale extractions due to its toxicity and flammability. In our study, we also investigated this solvent because it is known to be an excellent HPLC solvent for the analysis of anthocyanins. Even though acetonitrile is rarely used to extract plant bioactive components, our results showed that these extracts had the highest antioxidant activity. [PERSON] et al. (2002) also used acetonitrile extraction with acetic acid pickling. In their case, the total anthocyanin concentration of blackberries from the state of Georgia was 116.59 \(\pm\) 8.85 mg C3G/100 g FW, while the total polyphenol concentration was 486.53 \(\pm\) 97.13 mg GAE/100 g FW [28]. The least effective solvent was found to be 80 \(v/v\%\) ethanol even though, in our previous study, 50-70 \(v/v\%\) ethanol was the most effective solvent for blackcurrant by-products, and other literature data also showed 50 \(v/v\%\) ethanol to be the most effective [39]. This result can be explained by the fact that the extraction was carried out without acidification. [PERSON] et al. (2016) also used 80% ethanol as solvent, when the total anthocyanin concentration varied between 6.76 \(\pm\) 0.03 and 9.42 \(\pm\) 0.03 mg C3G/g FW, the total flavonoid concentration between 0.46 \(\pm\) 0.02 and 1.14 \(\pm\) 0.01 mg Q/g FW, while the total polyphenol concentration ranged from 8.23 \(\pm\) 0.16 to 14.98 \(\pm\) 0.54 mg GAE/g FW [23]. [PERSON] et al. (2005) used methanolic extraction with formic acid acidification. In their case, the total polyphenol concentration ranged between 292.2 and 446.4 mg GAE/100 g FW, depending on the blackberry ssp., which is very similar to our results [27]. For extracts obtained with acetone extraction, our results and the literature data do not always agree; however, the results of [PERSON] et al. (2002) (average of blackberry cultivars in the state of Oregon) are pretty close to our values since, in their case, the total anthocyanin content was 164 \(\pm\) 36 mg C3G/100 g FW, while the total polyphenol concentration was 577 \(\pm\) 56.1 mg GAE/100 g FW [26]. Despite the anthocyanins belonging to the group of flavonoids, in this case, the detected flavonoid content was lower than that of anthocyanins, although this should be inverse. A similar trend was observed by [PERSON] et al. (2016), indicating that the aluminum chloride colorimetric method cannot detect all flavonoids [23]. This theory is supported by [PERSON] et al. research.