# Nanoencapsulation of Essential Oils as Natural Food Antimicrobial Agents: An Overview
## 3 Essential Oils as Food Preservatives: Current Status and Challenges
### Challenges in the Use of EOs as Food Antimicrobials  
Due to their \"green\" nature, essential oils have received consumer attention for their use as a substitute for traditional food preservatives, which is a considerable market. However, EOs have a variety of internal and external critical challenges hindering their process as food preservatives: (i) EOs normally have low solubility in aqueous mediums and the reached concentrations are not able to exert significant biological activities; (ii) the scarcity of raw materials means that the quantity of EO obtained after extraction is generally insufficient for commercial applications; (iii) the high processing cost are also some of the major challenges; (iv) EOs are unstable due to their volatilization and oxidation, and thus are difficult to store, which may change the functional composition of active compounds (in actual production, it is necessary to rely on suitable carriers or adopt appropriate methods to achieve good antibacterial and fresh-keeping effects); (v) some EOs have a strong aroma even at low doses (in food systems, EOs can bind to lipids, proteins, and carbohydrates, so for a certain dose to achieve antibacterial effects, it may have a negative impact on food sensory qualities) [29]; and (vi) the collection and identification of plants, as well as the quality of raw materials, require a more systematic evaluation, especially safety assessment. There is still a lack of systematic research on the effects of plant EOs and their main components on the quality of food, fruit, and vegetable flavor [43]. Until now, most of the current studies are studying EOs as a whole or selecting single components in EOs. However, there are few studies about the interactions between various components and different EOs. Most of the research is carried out in the presence of a single microorganism and constant environmental conditions [26]. There are few studies on the coexistence of various microorganisms and the mode of action in food systems, because temperature, moisture, pH, and other factors in food products have a certain influence on the bacteria-static effect and can be a barrier factor. Therefore, it is necessary to conduct an in-depth study on the synergistic antimicrobial effect of the barrier factors [25]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Essential Oils** & **Bacteria Mechanism** & **Antimicrobial Activity** \\ \hline Cinnamon & Cinnamaldehyde can act on enzymes and cell wall. It can alter cell membrane permeability, inhibit ATPase active and amino acid synthesis, and deplete proton potential energy & 0.1–0.3\% (\(\varpi/\tau\)) cinnamon EO inhibited \(L\). _monocytogenes_ (6.0 log CFU/mL) [36]; 2.0\% (\(\varpi/\tau\)) cinnamon EO inhibited \(E\). _coli O157:H7_ (2.0 log CFU/mL) [37]. \\ \hline Marjoram & Ethanol steroids (protein denaturation and dehydration), leptin-4-opening (destruction of cell membrane results, leakage of intracellular substances) [38] & Antimicrobial activity against \(S\). _cervisiae, Fission yeast_, _Gotrichum candidum_, and _Pichia pastoris_ (MIC: 0.5–1.0, 0.0625, 0.5 and 0.5 ul/mL, respectively) [35]. \\ \hline Peppermint & Caused by menthone, menthol, menthol, menthol/ menthol/ acetate, limonene and \(\beta\)-pinene & Gasous peppermint EOs inhibits _E.