# Valorization of Carrot Pomace: UVC Induced Accumulation of Antioxidant Phenolic Compounds
## 3 Results and Discussion  
### Total Phenolics and Antioxidant Activity  
The effects of UVC radiation and storage time on the accumulation of total phenolics and the antioxidant activity of carrot pomace are shown in Figure 1. The total phenolic content of the carrot pomace obtained immediately after juice extraction was 1530 mg CHA equivalents kg\({}^{-1}\) (Figure 1A). Compared with most plant materials, carrot pomace contains a low content of total phenolics. For instance, blueberry, purple potato, and sweet cherry contain 41,800, 7810, and 20,980 mg/kg of total phenolics, respectively [22]. Similarly, the AOX of carrot pomace that is obtained after juice extraction was 5626 mg TE kg\({}^{-1}\) (Figure 1B), which is also low compared with other edible plant tissue such as green pepper (40,046 mg TE kg\({}^{-1}\)), broccoli (33,038 mg TE kg\({}^{-1}\)), and tomato (16,529 mg TE kg\({}^{-1}\)) [23]. The carrot pomace retained 51% of the total phenolics and 28.1% of the antioxidant activity from whole carrots, which have been previously reported to be around 3000 mg/kg and 20,000 mg/kg, respectively [24]. During storage, the carrot pomace that was non-treated with UVC (control) showed increases in the total phenolics by 241.6% and 709.5% at 24 h and 48 h, respectively, compared with the control before storage (CBS, Figure 1A). Regarding the AOX value, non-significant increases were detected at 24 h of storage, whereas at 48 h, the AOX increased by 80.1% in the control compared with the CBS (Figure 1B). The total phenolics observed after the storage of carrot pomace (12,390 mg/kg) reached higher values than those previously reported for whole carrots (3000 mg/kg) [24]. However, the AOX value observed in the stored carrot pomace (10,133 mg TE kg\({}^{-1}\)) was 51% of the value reported for whole carrots (20,000 mg/kg) [24]. To better understand the capacity of phenolics in carrot pomace to neutralize free radicals, the specific antioxidant activity was calculated (AOXs, Figure 1C). The AOXs is defined as the ratio of total antioxidant activity per total soluble phenolics and expressed as milligram of TE per milligram of CHA equivalents [25]. In this context, the AOXs of carrot pomace (3.67 mg TE/mg CHA equivalents) is 44.8% lower as compared with the AOXs of whole carrots [24], indicating that the phenolic compounds retained in carrot pomace after juice extraction have a lower capacity to neutralize free radicals. Furthermore, the AOXs decreased from 3.67 to 0.81 mg TE/mg CHA equivalents in the control (Figure 1C). This result indicates that the mixture of phenolics present in the carrot pomace before storage possesses a higher capacity to neutralize free radicals compared to the non-treated UVC stored tissue. The antioxidant activity of phenolic compounds depends on the number of hydroxyl groups present in their chemical structure [26; 27]. Therefore, their relative concentrations would determine how phenolics would interact to neutralize free radicals. These interactions could be synergistic, additive, or antagonistic [28; 29; 30]. The increase in phenolic content observed during storage of the carrot pomace that was non-treated with UVC radiation (control) could be attributed to the wound response of the plant tissue [31]. During carrot juice production, whole carrots are subjected to extreme wounding stress. The typical stress response of plants to wounding is the production of phenolic compounds, which serve as precursors for the lignin biosynthesis needed by the wounded tissue to decrease water loss [20; 32]. The accumulation of soluble phenolics in the tissue indicates that carrot pomace retains the metabolic machinery needed for phenolic biosynthesis, responding to extreme mechanical damage by producing phenolics as a stress defense mechanism.