# Plant-Derived Phytobiotics as Emerging Alternatives to Antibiotics Against Foodborne Pathogens
### Terpenes and Terpenoids  
Terpenes are a highly diverse and significant class of secondary metabolites found in plants, primarily as a major component of essential oils. They play a key role in various physiological and ecological functions, including a significant contribution to both biotic and abiotic stress responses [29; 30; 31]. They function as phytoalexins and allebotathic agents involved in plant defense mechanisms, ecological interactions, and environmental adaptation, mediating responses to pathogens, herbivores, and abiotic stressors such as drought or temperature fluctuations [32; 33]. Terpenes are a large group of organic compounds that are classified based on the number of isoprene units they contain (C\({}_{5}\)H\({}_{8}\), CH\({}_{2}\)=C(CH\({}_{3}\))CH=CH\({}_{2}\)). Depending on the number of these units, terpen are classified as monoterpenes (C\({}_{10}\), two isoprene units), sesquiterpenenes (C\({}_{15}\), three units), diiterpenenes (C\({}_{20}\), four units), sesquter terpen (C\({}_{25}\), five units), triterpenes (C\({}_{30}\), six units), and tetraterpenes (C\({}_{40}\), eight isoprene units) (Table 2) [31]. Terpenoids are terpenes modified, for example, by adding an oxygen atom or removing a methyl group. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Class** & **Number of Isoprene Units (C\({}_{5}\)H\({}_{8}\))** & **General Structural Formula** & **Examples** & **References** \\ \hline  & & & limonene, menthol, geraniol, myrcene, carvone, hinokitiol, linalol, carene, sabinene, camphene, thuijene, camphor, borneol, eucalyptol, ascaridole, umbellulone, \(\alpha\)-and \(\beta\)-phellandrene, terpinolene, \(\alpha\)-and \(\beta\)-pinene, ocimene, zingiberene, terpineol, isopulegool, citral, nerol, thymol, carvacrol, pulegone, verbenone, myrtenol, and isoborneol. & **Examples** & **References** \\ \hline  & & & limonene, menthol, geraniol, myrcene, carvone, hinokitiol, linalol, carene, sabinene, camphene, thuijene, camphor, borneol, eucalyptol, ascaridole, umbellulone, \(\alpha\)-and \(\beta\)-phellandrene, terpinolene, \(\alpha\)-and \(\beta\)-pinene, ocimene, zingiberene, terpineol, isopulegool, citral, nerol, thymol, carvacrol, pulegone, verbenone, myrtenol, and isoborneol. & **Examples** & **References** \\ \hline  & & & farnesol, nerolidol, codonolactone, hydroxyisoscotic acid, \(\beta\)-bisabolene, britannin, fumagalin, wildrol, zerumbone, \(\beta\)-elemene, guai-2-en-10\(\alpha\)-ol, \(\alpha\)-copaene, \(\alpha\)-humulene, \(\beta\)-caryophyllene, germacrene D, nerolidol, \(\beta\)-cubebene, nootkatone, \(\alpha\)-farnesene, lactucin, \(11\beta\),13-dihydrolatucin, lactupicrin, aubergenone, ketopelenolide b, and \(\delta\)-cadinene & **References** \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Classification of terpenes with general structures and examples. Monoterpenes and monoterpenoids (C10) are compounds built from two isoprene units and can be divided into acyclic (open-chain), monocyclic (one ring), and bicycle (two linked rings) [45]. While monoterpenes consist solely of carbon and hydrogen atoms (C\({}_{10}\)H\({}_{16}\)), monoterpenoids bear additional functional groups--alcohols, ketones, aldehydes, carboxylic acids, or phenolic moieties--that modify volatility, solubility, and bioactivity [34]. Commonly found in essential oils, they contribute strongly to plant aroma and flavor. Although not required for basic plant survival, they serve as defense chemicals (e.g., repelling insects or inhibiting microbial growth) and attract pollinators [45]. When administered to other organisms, they exhibit a broad spectrum of biological activities, including anti-inflammatory (e.g., limonene from citrus peels), antiviral, and antimicrobial effects. Pinene (from pine resin) supports respiratory function and exhibits anti-inflammatory properties. Another group is sesquiterpenes (C15), which consist of three isoprene units. Oxidation or rearrangement reactions lead to the formation of the corresponding sesquiterpenoids [38].