## 3 Results and Discussion
### Antioxidant Phenolic Compounds in Blackcurrants
Therefore, it is worth testing in the future whether the UVC length effect triggers a different mechanism in blackcurrants with a short exposure time. The quantities of catechin and epicatechin in blackcurrants ranged from approximately 500 to 3000 ng/g. Compared to the amounts before storage, the levels of catechin and epicatechin decreased after storage in most treatments except for 2 h UVC pretreatments. Catechin decreased from more than 1500 ng/g under 0 h, 0.5 h, and 1 h pretreatments to less than half of the original amounts. A similar reduction was also observed in the changes in epicatechin during storage. Earlier studies on green tea indicated that continuous 68 mJ/cm\({}^{2}\) UVC irradiation induced a minor decrease in the concentration of the most abundant catechin in green tea [54]. On the other hand, UVC irradiation of 720 Jm/m\({}^{2}\) could increase catechin synthesis in banana fruits [55]. In chokecherries, 2.3 J/m\({}^{2}\) UVC irradiation increased the content of catechin and epicatechin [56]. The UVC differential effects may be complex, which could be attributed to the type of fruit, UVC irradiation intensity, and duration. Figure 5: Heatmap of monophonic compound changes after UVC pretreatment. The heatmap uses tested values from LC-MS. The d0 and d20 represent the first and twentieth days of storage, respectively. The 0 h, 0.5 h, 1 h, and 2 h indicate the duration of UVC pretreatment. The darker the color in the heatmap, the higher the value of each compound data point. Four categories of phenolic compounds based on quantity are listed here: more than 1000 ng/g, 100–1000 ng/g, 10–100 ng/g, and 0–10 ng/g. Earlier research on the phenolic profile of blackcurrant extracts from fruits, leaves, and pomace only detected epigallocatechin in the leaves but not in the fruits and pomaces of blackcurrants [57]. In this study, we found that blackcurrants contained a certain amount of epigallocatechin, although there was not much difference in their quantities. Catechin, epicatechin, and epigallocatechin, as the major blackcurrant catechins in this study, might indicate the blackcurrant health benefit potential [58]. It has been reported that these polyphenolic compounds are highly associated with health promotion and antioxidant effects, including anti-obesity and anticancer functions [59; 58]. Delphinidin is one of the most common and essential anthocyanin molecules of flower pigments, and contributes to the antioxidant activity of blackcurrant fruits [60; 61]. Procyanidin B2, another pigment commonly found in plant seeds, fruits, and leaves, exhibits various bioactivities to prevent a wide range of human diseases, such as diabetes mellitus [62]. There were moderate amounts (100-1000 ng/g) of delphinidin, and procyanidin B2 were also detected in the blackcurrants. Procyanidin B2 showed a decreased amount under UVC pretreatments, but only slightly in the control (0 h-UVC). As catechin and epicatechin exhibit a nonlinear relationship with UVC treatment, the delphinidin content was not related to the irradiation duration. Specifically, 2 h UVC enhanced its content, whereas 1 h and 0.5 h-UVC reduced its amounts. Little UVC irradiation (0-0.5 h) may enhance the quercetin amount by 20 ng/g, but not with 1 h and 2 h UVC pretreatments, where a decrease in the amount was detected. The amounts of phenolic compounds between 10 and 100 ng/g included protocatechic acid, chlorogenic acid, naringenin, caffeic acid, gallic acid, kaempfer, ferulic acid, p-coumaric acid, and hydroxybenzoic acid. All these compounds are highly linked to remarkable antioxidant effects, which could further contribute to health promotion [63; 64; 65; 66; 67]. Among them, only chlorogenic acid showed a consistent reduction in concentration during storage under each treatment, decreasing from 20 to 40 ng/g. Chlorogenic acid is commonly found in green coffee extracts and tea, and it plays several critical therapeutic roles,  
Figure 6: The phenolic profiles in UVC-pretreated blackcurrants during postharvest storage.