# Application of Cinnamon Essential Oil in Active Food Packaging: A Review
## 5 Chemical Composition of Cinnamon Essential Oil
### Antimicrobial Activity
The antifungal activity of cinnamon EO has been demonstrated against various fungi and yeasts responsible for food spoilage such as _Aspergillus niger_, _Aspergillus flavus_, _Penicillium chrysogenum_, _Penicillium expansum_, _Penicillium citrinum_, _Mucor circinelloides_, or _Saccharomyces cerevisiae_, sometimes exceeding in efficacy other EOs such as oregano, lavender, garlic, ginger, eucalyptus, or rosemary [21]. Although EOs may have different modes of action, specifically, for cinnaldehyde, it has been suggested that it acts by inhibiting cell division [42]. On the other hand, most studies on antibacterial agents have aimed to achieve synergistic or additive effects through combined treatments. In medicine, drug combinations increase activity by using compounds with synergistic or additive effects, which thwart drug resistance and reduce required doses, thus decreasing adverse side effects and broadening the spectrum of activity [42]. Therefore, studying these effects in EOs is important to enhance antimicrobial activity without increasing the concentration of antimicrobial agents [45], enabling the design of novel, safe, and effective mixtures of antimicrobials and natural antioxidants for food preservation [49]. Combinations of EOs can cause synergistic, additive, or antagonistic effects depending on the composition and concentration of the components. The synergistic effect occurs when the antimicrobial activity of the antimicrobial mixture is greater than the sum of the effects of the individual components. There is considered to be an additive effect if the antimicrobial activity is equal to the sum of the effects of the individual components, and there is an antagonistic effect if the antimicrobial activity is less than the sum of the effects of the individual components [50]. Cinnamon EO shows different antimicrobial effects against foodborne pathogens when mixed with other EOs. It has been observed that when cinnamon EO is combined with oregano EO, it exhibits a synergistic effect against _S. typhimurium_ and an additive effect against _Salmonella_ spp., _E. coli_, and _L. monocytogenes_. When combined with thyme EO, a synergistic effect is observed against _Salmonella_ spp., _E. coli_, and _S. typhimurium_, and when combined with black pepper EO, this effect is seen against _L. monocytogenes_[46], although other authors have only observed an additive effect when cinnamon EO is combined with black pepper EO [51]. Furthermore, when this synergistic effect exists, a decrease of between two and six times the MIC value of the EO is observed, demonstrating the interaction between their compounds, allowing them to exert their antibacterial effect at lower concentrations [46]. Other studies have also confirmed the synergistic effects of cinnamon bark oil and ginger oil for _B. subtilis_[45]. The combined effect of cinnamon EO and clove EO has also been extensively studied, and, although significant synergy has been reported against _A. niger_[45], additive effects have generally been found against numerous bacteria such as _S. typhimurium_, _E. coli_, _B. subtilis_, _B. cereus_, _S. aureus_, or _L. monocytogenes_[46; 47; 51]. Synergistic effects tend to occur when the chemical composition of the EOs is different, as attacking different target sites simultaneously intensifies the antimicrobial effect. Additive effects usually occur when EOs have a similar chemical composition, since the action sites are similar [43]. In many plants, their chemical composition is very different between organelles, so the study of possible synergies between plant extracts from different parts of the same plant can be interesting. [PERSON] et al. [43] studied the combination of cinnamon leaf and bark EO, which have quite different chemical compositions, but only observed an additive effect against _L. monocytogenes_. Finally, the synergistic antibacterial activity of cinnamon EO with antibiotics has also been evaluated. Thus, [PERSON] et al. [52] revealed a synergistic effect against _E. coli_ and _S.