This work addresses two research topics: the first concerns the specific/sensitive trapping of hydroxyl radicals (•OH), and the second concerns the efficacy of encapsulating natural antioxidants, potentially lengthening their preservation activity. For context, nano-titania was solar-irradiated to produce•OH, which was spectrofluorimetrically assessed, based on the selective aromatic hydroxylation of the non-fluorescent sodium terephthalate to 2-hydroxyterephthalate fluorophore. Fluorescence intensity is proportional to generated•OH. Thus, a simple/rapid indirect method was utilized to assess•OH precisely. Accordingly, novel photoluminescent system is outlined in order to assess the scavenging potentiality of•OH in date seed oil (DSO) in both its pure and encapsulated formulations (ECP–DSO), i.e., when fresh and 5 months after extraction and encapsulation, respectively. With the addition of 80 μg/mL DSO or ECP–DSO, the efficacy of•OH scavenging amounted to 25.12 and 63.39%, which increased to 68.65 and 92.72% when 200 μg/mL DSO or ECP–DSO, respectively, was added. Moreover, the IC50 of DSO and ECP–DSO is 136.6 and 62.1 µg/mL, respectively. Furthermore, DSO and ECP–DSO decreased the kinetics for producing•OH by ≈20 and 40%, respectively, relative to•OH generated in the absence of antioxidant. This demonstrates the benefits of encapsulation on the preservation activity of natural antioxidants, even after five months after extraction, in terms of its interesting activity when compared to synthetic antioxidants. The developed fluorimetric•OH probing upgrades antioxidant medicines, thus paving the way for theoretical/practical insights on mechanistic hydroxyl radical-damaging biology.