## 3 Results and Discussion
### The acidity (pH) and Total Soluble Solids Values (\({}^{\circ}\)Brix)  
The active acidity of the carrot juices ranged from 6.33 to 4.21. The analyses carried out after 24 h revealed that the sumac powder addition and the cold plasma treatment increased the acidity of the juices in comparison with the control sample. The lowest pH was exhibited by samples supplemented with 3% of sumac powder. Sumac is rich in organic acids [49]; hence, the supplementation increased the acidity of the product. The time-point of the addition of sumac powder (before or after the cold plasma treatment) had no impact on the pH value. The lowest reduction in this parameter in relation to the control sample was observed in the plasma-treated juice without the sumac supplementation (P); in this case, an increase by approximately 0.6 units was observed. These changes are comparable with observations reported by other authors who found only a slight decrease in the pH of cold plasma-treated juices [50; 51]. This was probably associated with the generation of a small amount of acidogenic radicals during the cold plasma treatment.  
A statistically significant decrease in the pH value during storage was observed in the control sample. After 72 h, the value of this parameter decreased by 0.4, which could be related to the growth and acidifying effect of the juice microflora (Table 3) [52].  
The Brix degree (\({}^{\circ}\)Brix) is traditionally used in vegetable and fruit industries. After 24 h of storage, the mean value of this index was 8.40 for the unprocessed carrot juices and 8.27-8.73 for the CAP-treated products (P) or samples supplemented with the sumac powder (S05 and S3). Higher indices of total soluble solids were observed in samples P+05S and P+35. The addition of 0.5% of sumac powder combined with the plasma treatment proved to be a significant factor, as it contributed to an increase in the parameter on average to 10.33 \({}^{\circ}\)Brix. The highest value of total soluble solids, which was 25% higher than that in the control (C), was obtained in the variant supplemented with the maximum sumac powder concentration combined with the CAP treatment (SP3). The increase in total soluble solids may be due to the dissolution of compounds from sumac and probably the hydrolysis of insoluble compounds under the influence of energy supplied during processing. In general, the storage time did not exert a significant effect on this parameter (in most cases). Many researchers have reported a similar insignificant change in the level of total soluble solids in response to the cold plasma treatment of orange or apple juices [50; 53; 54]. As reported by [PERSON] et al. [53], soluble solids present in juices are mainly composed of carbohydrates, and it is difficult for active molecules produced in the plasma to reach these macromolecules within their short lifetime. In contrast to the above results, a significant increase in total soluble solids was noted in samples of freshly cut pears treated with plasma-activated water (PAW), where the increase was related to the conversion of starches to sugars [54]. In turn, [PERSON] et al. [55] reported a decrease in total soluble solids in PAW-treated Chinese blueberries.