# The Fermentation of Orange and Black Currant Juices by the
## 3 Results and Discussion  
### Orange and Black Currant Juice Parameters  
The basic parameters of the juices used in our experiments are shown in Table 1.  
Before designing the media for fermentation, the basic parameters of the juices (pH, extract, TPC, sugars, and organic acids) were assayed. The pH of the orange juice was equal to 4.18 \(\pm\) 0.12, while for the black currant juice, this parameter was equal to 3.57 \(\pm\) 0.11. The pH of the orange juice obtained in our study was a bit higher than the values reported by [PERSON] et al. and [PERSON] et al. (2018, 2019) (3.48); [PERSON] et al. (2019) (3.7); and [PERSON] et al. (2019) (3.55). The pH value for the black currant juice presented by [PERSON] et al. (2019) (2.96 \(\pm\) 0.05) was lower than the result assayed by us. Different orange cultivars, climatic parameters, harvesting time, and methods of juice extraction and preservation may cause these discrepancies. According to the literature, the total extract value of orange juice may vary, depending on cultivar, technology, and other factors, from 11.0 to 13.2 \({}^{\circ}\)Brix (2018, 2019, 2020, 2021). While for the orange juice the total extract result obtained by us (11.1 \(\pm\) 0.2) was consistent with the values reported by others, the Brix degree equal to 7.2 \(\pm\) 0.1 for the black currant juice obtained by us was only 50% of the values presented in the literature (2019, 2021) (14-16.6 \({}^{\circ}\)Brix); in addition to the abovementioned reasons for this difference, the additional elucidation of such a result may be the residual water present in the packaging line that was mixed with the head-part of the pumped juice and thus the extract content in this specific container was lower than expected by the manufacturer. The total phenolic compound of the orange juice was 49.61 \(\pm\) 0.63 mg GAE/100 mL, while for the black currant juice, the value of 85.7 \(\pm\) 0.34 mg GAE/100 mL was noted. According to the literature, the TPC value of the specific fruit juice depends on the cultivar and method of juice extraction. A broad range of TPC values for orange juice, ranging from 18.68 mg GAE/100 mL (2021) to 76.8 mg GAE/100 mL, was reported (2021, 2021). According to the literature, black currant juice may contain as little as 36.7 mg GAE/100 mL (2021) and as much as 350 mg GAE/100 mL (2021, 2021). The values of the TPC obtained in our study fell within this range. The glucose, fructose, and organic acids presented in Table 1 were determined in the juices using the HPLC technique. The concentration of glucose and fructose in the orange juice was 43.69 \(\pm\) 1.22 and 47.39 \(\pm\) 1.07 g/L, respectively; for the blackcurrant juice, the concentration of these sugars was 28.46 \(\pm\) 0.92 and 30.5 \(\pm\) 1.03 g/L, respectively. The content of these sugars, crucial for alcoholic fermentation, was similar to the results described by [PERSON] et al. (2019) for black currant juice (fructose 36.7 and glucose 33.7 g/L) and the results reported by [PERSON] et al. (2019) (total reducing sugars 48.5 g/L) and [PERSON] et al. (2019) (glucose 57.81 and fructose 56.25 g/L) for orange juice. [PERSON] et al. (2019) reported that the total sugar concentration for orange juice was equal to 70 g/L, which was also consistent with our results presented in Table 1. Organic acids are critical compounds for the flavor bouquet of alcoholic beverages. They are formed due to plant metabolic activity and are also created and utilized by the microflora present during fermentation. The contents of the three acids that we were able to identify using HPLC chromatography presented in Table 1 provide a reference for the concentrations of these acids in the post-fermentation samples in Tables 2 and 3. The predominant acid in the juices was citric acid, its concentrations being 8.51 \(\pm\) 0.57 and 5.57 \(\pm\) 0.23 g/L for the orange and currant