Due to the increased bacterial resistance against antibiotics and side-effects of chemical drugs, the use of medicinal plants with antimicrobial properties has gained importance in disease treatment (
15). According to the results of the present study, ethanol and methanol polar solvents could extract the compounds with antibacterial activity, such as aromatics, flavonoids, and flavonols, which were dissolved in the methanol and ethanol solvents (
24,
25). In addition, the methanol extract of
C. grandis exerted more significant inhibitory effects compared to the ethanol and aqueous extracts.
The literature search revealed that no prior studies have been focused on the antimicrobial activities of
C. grandis in Iran. Meanwhile, the antimicrobial activity of ethyl acetate, butanol, and the methanol extracts of the white and colored skin of
C. grandis has been investigated using the disc-diffusion method against
S. aureus,
B. cereus,
B. subtilis, and
E. coli (
26). According to the findings, the methanol extract of the colored and white skin of
C. grandis showed better inhibitory activities against
B. cereus and
S. aureus, which is consistent with our findings.
In a study in this regard, Mokbel and Suganuma investigated the antimicrobial activity of 80% and 100% methanol extract of
C. grandis white skin against
S. aureus,
B. subtilis,
B. cereus,
M. luteus, and
E. coli (
5). According to the mentioned research, 80% methanol extract had more significant antibacterial effects compared to the pure methanol extract, and
S. aureus had the highest susceptibility. In addition, the level of free radicals was estimated to be 74.5%, which in line with the present study. Several factors could affect antimicrobial activity, such as the extraction method, environmental conditions, plant genotype, moisture content, extraction time, and powder size (
27). In the current research, the serial diffusion method yielded more accurate results compared to the disc-diffusion and agar well diffusion methods (
28).
Citrus fruits contain high levels of phenolic compounds and ascorbic acid (
29,
30). According to the findings of Gorinstein et al. (
31), the flavonoid content of lemon, orange, and grape fruit is 1.9, 1.8, and 1.6 mgGA/g, respectively. The discrepancy between the mentioned study and our findings could be due to the differences in the species type, environmental conditions, and different compounds. In another research, Mathur et al. (
32) reported the total phenol content of the skin ethanol extract of
C. sinensis,
C. maxima, and
C. reticulata to be 0.13, 0.02, and 0.14 mgQ/g, respectively. Furthermore, Ghasemi et al. (
33) reported the total flavonoid content of the skin methanol extract of 13 species from Iran to be within the range of 0.3 - 31.1 mgQ/g and the IC
50 content to be within the range of 0.6 - 2.9 mg/mL; the IC
50 content obtained in the mentioned study is consistent with our findings. On the same note, Fatahimoghadam et al. (
34) reported the total flavonoid content of the skin methanol extract of six citrus fruits from the north of Iran to be within the range of 2.65 - 7.68 mgQ/g and the free radical inhibition percentage within the range of 68.58 - 95.77%, which is consistent with the results of the present study.
Considering the higher solubility of active compounds with antimicrobial properties in methanol solvents (
35), we used the methanol extract to detect the presence or absence of secondary metabolites. In this regard, Tian-Shung et al. (
36) assessed the presence of alkaloids by an acetone extract, and Okwu et al. (
37) evaluated the presence of tannins, alkaloids, and saponins by the diethyl ether extract of
C. grandis skin; the results of the mentioned studies are consistent with our findings. In another study, Mishra et al. (
38) detected the presence of tannins and saponins by the methanol extract of
C. limetta skin using a phytochemical method. In addition, Sheikhlar et al. (
39) reported the presence of alkaloids (consistent with our findings) and tannins, as well as the absence of saponins (consistent with our findings in the colored skin extract) by the skin methanol extract of
C. limon using a phytochemical method. Similarly, Pandey et al. (
16) reported the presence of tannins (contrary to our findings) and absence of saponins by the skin and seed methanol extract of
C. limon. Pathan et al. (
40) also reported the presence of tannins and alkaloids by the leaf and skin hydro-alcoholic extract of
C. aurantium. The difference in the presence and absence of secondary metabolites in various plants depends on the variations in the species type, extract and solvent, environmental conditions, and extraction methods (
41).
5.1. Conclusions
According to the results, the extract of C. grandis had antibacterial and antioxidant activities owing to the presence of secondary metabolites. Therefore, it is recommended that by the processing and extraction of antimicrobial compounds from the extract of this plant, C. grandis be used in the pharmaceutical industry as an antibiotic to control human pathogenic bacteria.