## 3 Biological Activities
### Antifungal Activity
The antifungal effect can be attributed to the alteration of the integrity and permeability of the cell membrane, which can cause irreversible damage to the cell wall and membrane. They can also destroy yeast proteins and inhibit their synthesis. The results have indicated that EOs can effectively inhibit the growth of food-related microorganisms, and there is great potential for applying EOs to the food industry. The authors mention that the effect of terpen on the germination capacity of _Z. rouxii_ spores should be studied. On the other hand, the possible antifungal mechanism of citral against _Candida albicans_ (a yeast that inhabits the human body in a commensal way and can cause opportunistic or pathogenic infections) has also been investigated. The MIC (64 \(\mu\)g/mL) and MFC (256 \(\mu\)g/mL) of citral required only 4 h of exposure to effectively kill 99.9% of the inoculum. Citral's mechanism of action did not involve the cell wall or ergosterol (Figure 3). However, in the morphological interference test, the product inhibited the formation of _pseudohydphae_ and _chlamydoconidia_. Antibiofilm Activity of Citral against Fungi  
In addition to the antifungal effect, an antib biofilm potential is another activity widely reported for citral. In this regard, citral obtained from _Melissa officinalis_ effectively inhibited the growth of _C. albicans_ (MIC = 500 mg/L). Still, it was also able to reduce the formation of mature biofilms by 50% at a concentration of 1000 mg/L [83]. Similarly, terpenoid exposure prevented _C. albicans_ from adhering to polystyrene surfaces. Citral, geraniol, thymol, and carvacrol were metabolic activity studies' most active adhesion inhibitors. Furthermore, they were moderately effective in inhibiting mature biofilms at <2 mg/mL MIC. The results obtained in 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide sodium salt (XTT) test were also confirmed by the crystal violet test, where a >50% reduction in absorbance compared to the control indicated the elimination of the biofilm network due to treatment with these terpenoids [83]. Similarly, the EOs of _C.citratus_and _Syzygium aromaticum_ rich in citral and other terpen showed that most of the _C. albicans_ strains tested displayed the formation of moderate to strong biofilms. Preformed _Candida_ biofilms showed \(\geq\)1024 times increased resistance to antifungal drugs. It was two times for _S. aromaticum_, but no increased tolerance for _C. citratus_. The oils were more active against preformed biofilms compared to amphoteric B and fluconazole. At 0.5\(\times\) MIC, _C. citratus_, followed by _S. aromaticu_, were most inhibitory against biofilm formation. Light and electron microscopic studies revealed the deformity of three-dimensional structures of biofilms formed in the presence of sub-MICs of _C. citratus_ (MIC of oils against planktonic cells ranged from 200 to 360 and 100 to 180 g/mL). The cell membranes appeared to be the target site of compounds in sessile cells, as displayed by SEM observations [84]. In the same way, the essential oil of _L. cubeba_ (Lour.) Pers. (contains citral and other terpen) was effective in inhibiting the formation of biofilms and mature biofilms of different _Candida_ species by at least 50%, among these are _C. albicans_ (2000 mg/L), _C. glabrata_ (2000 mg/L), _C. krusei_ (250 mg/L), _C. orthopsilosis_ (2000 mg/L), _C. parapsilosis_ (1000 mg/L), and _C. tropicalis_ (2000 mg/L) [85]. Another widely analyzed microorganism is _C. tropicalis_; it has been demonstrated that citral can inhibit biofilm formation (IC\({}_{50}\): 64 mg/mL) and eradicate preformed biofilms (EC\({}_{50}\): 128 mg/mL) of C. _tropicalis_. Another study compared the influence of citral and thymol on _C. tropicalis_ and its biofilm and the expression levels of certain antifungal tolerance genes. Interestingly, it was observed that both citral (MIC\({}_{50}\) = 32 mg/mL) and thymol (MIC\({}_{50}\) = 16 mg/mL) exhibited significant effectiveness against planktonic cells of _C. tropicalis_.