# Valorization of Carrot Pomace: UVC Induced Accumulation of Antioxidant Phenolic Compounds
## 3 Results and Discussion
### Total Phenolics and Antioxidant Activity
Figure 1: Total phenolic content (**A**), antioxidant activity (**B**), specific antioxidant activity (**C**), and correlation of antioxidant activity against phenolic content (**D**) of carrot pomace treated with UVC for 0 (control), 30, 60, or 120 min, and stored at 25 \({}^{\circ}\)C for 48 h. Data represent the mean of 3 repetitions \(\pm\) the standard error of the mean. Different letters among bars (a, b, c, d, e, f, and g) indicate a statistical difference between treatments using the LSD test (\(p<0.05\)). Abbreviations: CHA: chlorogenic acid; TE: Trolox equivalents. The application of UVC radiation did not induce an immediate change in the total phenolics (Figure 1A) and antioxidant activity (Figure 1B) of carrot pomace. These results agree with a previous report, where the application of UVC radiation did not modify the total phenolic content in carrot slices, pie-cuts, and shreds [8]. Interestingly, the carrot pomace treated with 120 min of UVC radiation showed a slightly higher amount of AOXs than the CBS (Figure 1C), indicating that UVC light modified the phenolic profile, generating a combination of compounds with a higher capacity to neutralize free radicals. At 24 h of storage, the concentration of soluble phenolics increased in all samples, while carrot pomace subjected to 60 min of UVC light showed the lowest increase (Figure 1A). At 48 h, the tissue treated with 30 min of UVC light did not show a further increase in total phenolics, while the carrot pomace treated with 60 and 120 min of UVC continued to increase. No significant difference was detected in the phenolic content between the 120 min UVC treatment and the control, whereas the 60 min UVC treatment showed a slightly lower (\(-14.6\%\)) accumulation of total phenolics (Figure 1A). The antioxidant activity showed a similar behavior (Figure 1B), indicating that the phenolic compounds are the main contributors to the AOX value of carrots (Figure 1D). This is demonstrated with the \(R^{2}\) value obtained for the correlation of AOX against the total phenolics (\(R^{2}\) = 0.8782, Figure 1D), which was higher than 0.7 [25]. The combined effect of wounding and UVC radiation to induce the biosynthesis of phenolic compounds in carrots has been previously reported [8; 9]. The authors determined the mechanism by which the tissue responds to the combination of both stresses, leading to the accumulation of phenolics. In wounded carrot tissue, UVC radiation induces the production of reactive oxygen species (ROS), and together with ethylene and jasmonic acid, which are produced as a response to wounding stress, activates the expression of genes and enzymes related to the biosynthesis of phenolic compounds [9]. A similar phenomenon could occur in carrot pomace that is treated with UVC radiation, where both stresses are combined. Interestingly, UVC radiation did not induce a higher accumulation of total phenolics compared to the control. The soluble phenolics quantified in the tissue result from a balance between their biosynthesis rate and their utilization rate for the production of other metabolites such as lignin [20; 21]. Likewise, it also depends on the availability of the carbon source needed for their biosynthesis [33; 34]. Therefore, it is likely that depending on the dose of UVC radiation applied, the concentration of signaling molecules that modulate different mechanisms in the tissue are activated. For instance, results suggest that samples treated with 30 min of UVC radiation present a higher lignification rate than the control, while higher UVC doses also increase the phenolic biosynthesis rate, displaying a similar behavior to the one observed in the control. Furthermore, results also suggest that the carbon source is the limiting factor in obtaining a higher accumulation of phenolics in the tissue since the carrot pomace treated with UVC radiation did not show a higher phenolic content compared to the control at 48 h of storage.