Antifungal, Antioxidant, and Irritative Potential of Citronella Oil (Cymbopogon nardus) Associated with Phenethyl Ester of Caffeic Acid (CAPE)

The present study aimed to analyze the antifungal, antioxidant, and irritant potential of citronella oil, both isolated and combined with caffeic acid phenethyl ester (CAPE), for topical oral candidiasis. The antioxidant potential was evaluated using two methods, the DPPH test and the reducing power test (FRAP), while the irritant potential of the solutions was assessed through the hen’s egg chorioallantoic membrane test (HET-CAM). The DPPH test (IC50) values for the CITRO III + CAPE III combination were 32 ± 9 mg/mL, and for isolated CAPE, 13 ± 3 mg/mL. The results from the FRAP method revealed a low iron-reducing power for the combination of 1.25 mg/mL of citronella and 0.0775 mg/mL of CAPE (CITRO III + CAPE III), showing no significant difference compared to the isolated solution of 0.15 mg/mL of CAPE. The antibacterial activity of CAPE and isolated citronella in vitro against microorganisms was evaluated using two methods: microdilution and biofilm assay. The results showed that the MIC and MFC values were 0.5 mg/mL for citronella at both tested times (24 h and 48 h). For CAPE, the MFC values were 0.031 mg/mL. For the biofilm assay, the isolated compounds and combinations at 1 min and 6 h showed significantly different results from the controls (p < 0.05). Furthermore, the HET-CAM results demonstrated the absence of irritability. Based on these premises, the antifungal and antioxidant actions, and absence of irritability were proven. Moreover, this work presents a natural antifungal of interest to the pharmaceutical industry.