# Recent Advances in the Antibacterial Activities of _Citrullus_ _Ianatus_ (Watermelon) By-Products
## 4 Antibacterial Activities of _Citrullus Ianatus_ By-Products
### Rind and Peel
In fact, it shows a higher antibacterial capacity compared with other species of the genus Streptococcus, making water and boiling suitable extraction methods to combat the activity of _S. mutans_. An approach that could be considered quite useful is the study of [PERSON] et al. [PERSON] et al. (2018), who studied the action of the most well-known and commonly used solvents, acetone, methanol, ethanol, and water, which also show a range of polarity on the antibacterial capacity of watermelon peel. For the production of extracts, the peel was removed from the rest of the fruit and cleaned with tap water, while it was sterilized with a 70% ethanol solution and rinsed with sterile distilled water. The peels were then cut to approximately 1 \(\times\) 1 cm and dried in a vacuum dryer at 50 \({}^{\circ}\)C and 0.0045 mbar pressure for 48 h. Thereafter, _C. lanatus_ peels were pulverized and weighed, and four extracts were prepared with four different solvents. For the first one, 100 mL of methanol (80%) was used; for the second, 100 mL of acetone (80%); for the third, 100 mL of ethanol (80%); and for the fourth, 100 mL of distilled water. Extraction was carried out by stirring at 22 \({}^{\circ}\)C at 130 rpm for 24 h. Each extract was filtered and concentrated using a rotary evaporator, except for the water extract, which was concentrated in a water bath at 90 \({}^{\circ}\)C for 30 min. The antibacterial activities of the extracts were tested against two Gram-positive bacteria, namely _B. cereus_ and _Listeria monocytogenes_, and six Gram-negative bacteria, namely _S. aureus_, _E. coli_ O157:H7, _E. coli_, _P. aeruginosa_, _Salmonella enteritidis_, and _S. typhimurium_. Penicillin G was also utilized as a positive control to ensure the validity of the results. As for the results, interesting findings were observed. In particular, the most remarkable finding was that for the Gram-negative Salmonella bacteria. Only the positive control showed inhibition activity (>15 mm). Regarding the other bacteria, in _B. cereus_ the ideal solvent for generating extracts with antibacterial capabilities was found to be methanol (~20 mm), while for _E. coli_ O157:H7 and _E. coli_, methanol was found to be the most suitable solvent with inhibition zones of ~20 and ~30 mm. Regarding the other Gram-positive bacteria _L. monocytogenes_, ethanolic peel extract was found to be the ideal one with an inhibition zone of ~20 mm; similar results were obtained for _S. aureus_. The only extract that showed antibacterial activity was the one prepared with ethanol solvent at an inhibition zone of 15 mm. At this point, it is worth mentioning that ethanol as a solvent also had essential results on _E. coli_ O157:H7, with an interception zone identical to that of the methanol extract. Finally, the ethanol extract was also found to have greater activity against the bacterium _P. aeruginosa_, with an inhibition zone of more than 15 mm. In conclusion, it is worth emphasizing that both water and acetone are not suitable for the preparation of extracts with strong antibacterial activity, as against most bacteria (_S. aureus_, _E. coli_ O157:H7, _P. aeruginosa_, _S. enteritidis_, and _S. typhimurium_), no inhibitory activity was observed. Finally, in both _E. coli_ O157:H7 and _E. coli_, the positive control showed a lower zone of inhibition than the methanolic extracts of watermelon peel. The most recent research was carried out by [PERSON] et al. [101], which presented, apart from remarkable results, a new, interesting, and nutritious product. In particular, a candy was prepared from find extract. The preparation of the extract required drying by osmotic dehydration, cutting into small pieces, and leaving them to dry in front of an oven operated at 60 \({}^{\circ}\)C for 24 h. The dried rind was turned into a fine powder and sieved. Extraction took place at RT for 24 h using an orbital stirrer, where watermelon rind powder was added to a flask containing 80% aqueous ethanol in a solid-to-liquid ratio of 1:10.