Evaluation of Antioxidant, Xanthine Oxidase-Inhibitory, and Antibacterial Activity of Syzygium cumini Linn. Seed Extracts

<i>Syzygium cumini</i> (L.) Skeels, commonly known as the Jamun or Indian blackberry, is a tropical evergreen tree native to the Indian subcontinent, and it belongs to the Myrtaceae family. This research aimed to assess the antibacterial properties of the extracts derived from <i>S. cumini</i> seed kernels and evaluate their total flavonoid content, total phenol content, total carbohydrate content, antioxidant capacity, and inhibitory effects on xanthine oxidase. Cold maceration was chosen for its ability to preserve thermolabile compounds and efficiently extract bioactive constituents with minimal energy and equipment requirement, with hexane and methanol employed as extraction solvents. The methanolic seed kernel extract of <i>S. cumini</i> showed the highest flavonoid (127.78 μg quercetin equivalent/mg dried extract vs. 21.24 μg quercetin equivalent/mg in hexane dried extract) and polyphenol content (153.81 μg gallic acid equivalent/mg dried extract vs. 38.89 μg gallic acid equivalent/mg in hexane dried extract), along with significant carbohydrate content (475.61 μg glucose equivalent/mg dried extract vs. 5.57 μg GE/mg in hexane dried extract). It also demonstrated potent antioxidant activity (IC₅₀: 9.23 μg/mL; ascorbic acid: 5.10 μg/mL) and xanthine oxidase inhibition (IC₅₀: 14.88 μg/mL), comparable to the standard drug allopurinol (IC₅₀: 6.54 μg/mL), suggesting its therapeutic potential. Moreover, the methanolic extract of seed kernels exhibited strong antibacterial activity, with inhibition zones of 19.00 mm against <i>S. epidermidis</i>, higher than the standard antibiotic (gentamicin: 18.33 mm) against <i>K. pneumonia</i> (ciprofloxacin: 33.66 mm). The lowest minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of 0.32 mg/mL and 0.52 mg/mL, respectively, were observed for the same extract against <i>S. epidermis</i>. In conclusion, this study demonstrated the remarkable antibacterial effects of <i>S. cumini</i> methanolic seed kernel extract against various pathogenic microorganisms as well as significant inhibitory effects on xanthine oxidase and antioxidant activity.