# Recent Advances in the Antibacterial Activities of _Citrullus_ _Ianatus_ (Watermelon) By-Products
## 4 Antibacterial Activities of _Citrullus Ianatus_ By-Products
### Seeds
The diminished potency of the extracts on specific bacterial strains may be attributed to the limited presence of phyto-chemicals at a low concentration. The extracts possess inherent potential, necessitating additional research. The production of watermelon seed protein hydrolyzed (WPSH) was conducted in a study conducted by [PERSON] et al. (1993). They aimed to investigate the impact of varying concentrations of WSPH (0, 1, 2, and 3%) on the overall quality of silver carp (_Hypophilthalthys molitrix_) burgers during a period of refrigerated storage at a temperature of 4 \({}^{\circ}\)C. Defatted watermelon seeds were processed with 0.1 N NaOH, and the precipitated protein isolate was collected. The findings associated with the levels of total viable count (TVC) and psychotrophic count (PTC) showed consistency and statistically significant increases (\(p<0.05\)) across all treatments over the course of the 16-day storage duration. It was observed that the control group exhibited the highest level of bacteria (TVC: \(\sim\)10 log CFU/g, PTC: \(\sim\)9 log CFU/g) in the fish burger, while the treatment group containing 3% WSPH showed the lowest level (TVC: \(\sim\)6 log CFU/g, PTC: \(\sim\)6.5 log CFU/g). This significant difference suggests that the peptides possess antibacterial properties, which are of high importance. According to the International Commission on Microbiological Specifications for Foods (1993), it is recommended that the permissible level of PTC and TVC not exceed 7 log CFU/g. In accordance with the results, the burgers treated with 3% WSPH showed sustainability throughout the whole storage duration. The mode of action of antibacterial peptides is predominantly attributed to the electrostatic interaction between peptides and the cell membrane of microorganisms. They have the ability to penetrate the membrane and subsequently cause its disruption. Moreover, [PERSON] et al. (2015) asserted that the antibacterial efficacy of bioactive peptides could potentially be attributed to their ability to chelate iron. Hence, the utilization of WSPH as a natural antibacterial agent presents a viable approach to extending the longevity of fish burgers. This application enables an approximate extension of the shelf life by 8 days when stored under refrigeration conditions. The findings of the mentioned studies are summarized in Table 2. \begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Gram**} & **Strain of Bacteria** & \multirow{2}{*}{**Solvent**} & \multirow{2}{*}{**Extraction Conditions**} & **MIC (mg/mL)** & \multirow{2}{*}{**Zone of Inhibition**} & \multirow{2}{*}{**Ref.**} \\  & & & & & & \\ \hline \multirow{2}{*}{+} & _B. cereus_ & 1 M NaOH & Precipitation & n.a. & 0 & [107] \\  & Methanol & & & 25 & 3.91 & [96] \\ \hline \multirow{2}{*}{+} & \multirow{2}{*}{_B. subtilis_} & Ethyl acetate & Maceration for 72 h & 2.5 & 26 & [105] \\  & Methanol & Mechanical shaking for 24 h at RT & 8 & 14.5 & [9] \\  & Methanol & Maceration for 24 h at RT & 250 & 0 & [112] \\  & Water & Maceration for 48 h & 25 & 16 & [109] \\ \hline \multirow{2}{*}{\(-\)} & _Bacteroides_ & 1 M NaOH & Precipitation & 6 & n.a. & [110] \\  & _fragilis_ & 1 M NaOH & Precipitation & 2.5 & n.a. & [110] \\ \hline \multirow{2}{*}{+} & _C. perfringens_ & 1 M NaOH & Precipitation & n.a. & 11 & [107] \\  & _E. faecalis_ & Methanol & Mechanical shaking for 24 h at RT & 8 & 12 & [9] \\  & Methanol & Maceration for 24 h at RT & 250 & 9 & [112] \\ \hline \end{tabular}
\end{table} 
Table 2: Antibacterial activity of different watermelon seed extracts.