# Recent Advances in the Antibacterial Activities of _Citrullus_ _Ianatus_ (Watermelon) By-Products
## 4 Antibacterial Activities of _Citrullus Ianatus_ By-Products  
### Rind and Peel  
The first survey of the current topic was carried out by [PERSON] et al. [93]. The aim of the study was to investigate the applicability of using local watermelon rind modified with clove as an adsorbent for microorganisms and toxic heavy metals in wastewater. Watermelons purchased from a local fruit market were washed with tap water, and the rind was removed and left to dry in the sun. In the rind studied, metals were removed (by injection with 5% HNO\({}_{3}\)), and pH 6.5-7.5 was ensured by washing with water at 60 \({}^{\circ}\)C. The sample was composed of dried rind, which was boiled with the clove extract. For antibacterial evaluation (population of total coliform and _Escherichia coli_), a batch method of varying the mass of modified watermelon rind in three different masses of 3, 5, and 7 g of the sample was used. Specifically, 100 mL of wastewater was mixed with a modified biosorbent, and the mixture was shaken for 24 h in aerobic conditions at 125 rpm at RT. Observing the results, the total coliform (TC) and _E. coli_ populations were found to be 89 \(\times\) 10\({}^{6}\) for the former and 68 \(\times\) 10\({}^{6}\) for the latter. By using 5 g of clove and 3 g of rind for the preparation of extracts, the population decreased to 1000 for TC and 200 for _E. coli_. Keeping the mass of clove constant, when 5 g of rind was used, the population decreased even more, to 200 for TC and 40 for _E. coli_, while at the same time, when the amount of watermelon rind was 7 g, the microbial population was detected only for TC, while the action of _E. coli_ was completely inhibited. In conclusion, when clove was increased to 7 and 8 g in the extracts, the population of TC and _E. coli_ was intercepted entirely, indicating that adding herbs was of great significance because it significantly increased the antibacterial activity of the rind extract. Furthermore, in this research, it was shown that the rind of watermelon itself has antibacterial properties since increasing its amount enhanced the control of bacterial activity. In addition, _C. Ianatus_ peel is often reported to possess a wide range of antibacterial properties since it contains terpenoid, alkaloid, flavonoid, saponin, tannin, terpenoid, and phenolic compounds, whose main role is to protect and defend plants against bacteria [94]. However, the initial study to quantify the antibacterial activity of the peel was carried out by [PERSON] et al. [94], investigating the activity of the peel on a Gram-positive bacterium, _Staphylococcus epidermidis_, using the disc diffusion method. Two solvents, methanol and hexane, were used to prepare the extracts through maceration in order to find the most suitable one. Regarding methanol, the antibacterial discs were injected with five different extract concentrations of 20, 40, 60, 80, and 100 mg/mL, while regarding hexane, the first four concentrations were tested. The assessment of antibacterial activity was based on zones of inhibition (in mm). Commercial ampicillin was used as a positive control for bacteria. In methanolic extracts, the inhibition zones for _S. epidermidis_ were \(\geq\)10 mm, 5-9 mm, 5-9 mm, 5-9 mm, 5-9 mm, and 0 mm for the concentrations 20, 40, 60, 80, and 100 mg/mL, respectively, while the ampicillin showed a \(\geq\)10 mm inhibition zone. Furthermore, in hexanoic extracts, the inhibition zones were \(\leq\)4 mm, \(\leq\)4 mm, 5-9 mm, and 0 mm for the concentrations 20, 40, 60, and 80 mg/mL, respectively. Last but not least, ampicillin showed a zone of inhibition in the range of 5-9 mm, i.e., a moderate inhibition zone. It should be noted that the authors describe \(\leq\)4 mm as a weak inhibition zone, 5-9 mm as a moderate inhibition zone, and \(\geq\)10 mm as a strong inhibition zone. Considering the results, methanol appears to be a better solvent than hexane. However, the lower the concentration of the extract, the stronger the antibacterial activity, with an ideal concentration of 20 mg/L.