# Recent Advances in the Antibacterial Activities of _Citrullus_ _Ianatus_ (Watermelon) By-Products
## 4 Antibacterial Activities of _Citrullus Ianatus_ By-Products
### Seeds
aeruginosa_ was inhibited by the presence of wheat germ oil. The efficacy of black cumin seed oil against _S. aureus_ has been demonstrated. The remaining cosmetic oils that were tested exhibited negligible antibacterial activity against the selected microorganisms under investigation. Furthermore, their efficacy in inhibiting the proliferation of bacteria and yeast was significantly inferior to that of tea tree oil. The antibacterial properties of the oils under investigation exhibited variability, which was contingent upon both the specific oil type and the microorganism employed in the experimental analysis. However, it should be noted that no antibacterial properties were found for cold-pressed watermelon seed oil, so further investigation should be done on this cold-pressed oil. The nutritional value and therapeutic potential of watermelon seeds have been acknowledged; however, to date, no studies have been conducted to isolate and quantify melanin content. To that end, [PERSON] et al. [107] assessed the antioxidant and antibacterial properties of raw and purified (defatted) melanins extracted from watermelon seeds. Melanin was precipitated after treatment with sodium hydroxide (NaOH) and hydrochloric acid (HCI). L-DOPA melanin was used as a positive control. The microorganisms under investigation included Gram-positive bacteria _B. cereus_, _E. faecalis_, and _S. aureus_, along with Gram-negative bacteria _E. coli_ and _P. aeruginosa_. The results showed that the purification of melanin increased the antioxidant activity of the extracts. For instance, 1 mg/mL of purified melanin had 92.48% antioxidant activity, while raw melanin had 79.18%. The positive control had 97.16% antioxidant activity. The antibacterial activity was assessed through zones of growth inhibition, in which it was revealed that only _E. faecalis_ and _P. aeruginosa_ recorded ~11 mm and ~13 mm, respectively, regardless of the extract used. Consequently, the observed antibacterial properties of extracted melanin from _C. lanatus_ seeds indicate its potential therapeutic efficacy in the traditional medicinal use of this plant in treating bacterial nilments such as diarrhea, gastrointestinal infections, respiratory disorders, and dermatological conditions. [PERSON] et al. [108] examined the chemical composition, nutritional assessment, and antibacterial properties of _C. lanatus_ seeds. Watermelon seed powder was subjected to maceration with methanol at a 4:1 liquid-to-solid ratio for 24 h at RT. The methanolic watermelon seed extract was subjected to quantitative analysis, revealing the presence of alkaloids at a concentration of 3.08 mg/g, polyphenols at 0.30 mg/g, tannins at 0.12 mg/g, saponins at 0.20 mg/g, and flavonoids at 2.67 mg/g. The vitamin B complex content of watermelon seeds was found to be 0.03 mg/100 g for vitamin B\({}_{1}\), 0.01 mg/100 g for vitamin B\({}_{2}\), 0.64 mg/100 g for vitamin B\({}_{3}\), 0.24 mg/100 g for vitamin B\({}_{6}\), and 0.01 mg/100 g for vitamin B\({}_{12}\). The bioactivities of the extract were assessed against a range of bacterial strains, including Gram-positive bacteria such as _B. cereus_, _S. aureus_, _Tsukamurella hongkongensis_, _Lactobacillus_ spp., _Staphylococcus petrasii_, and _Dietzi amaris_, along with Gram-negative bacteria such as _Proteus mirabilis_, _E. coli_, _Necropsobacter rosorum_, _Neisseria sica_, _Pseudomonas oryzaehabitans_, _Klebsiella pneumoniae_, _Adventella incenata_, _Neiseria subflava_, and _Serriatia marcescens_. The antibacterial activity of the extract revealed that not all of the tested organisms showed susceptibility. _Lactobacillus_ spp. and _P. oryzaehabitans_ had 12 and 16 mm of inhibition growth zones at 300 mg/mL of the extract. Regarding three gram-negative bacteria, _N. sica_, _N. rostrum_, and _N. sica_ had inhibition growth zones of 18, 13, and 17, respectively, at 200 mg/mL. An interesting finding was that all three of them did not show any inhibition growth zone at 300 mg/mL.