# D-Limonene: Promising and Sustainable Natural Bioactive Compound
); [EMAIL_ADDRESS] (W.X)  
Yingu Zhang  
1 College of Food and Bioengineering, Xilhua University, Chengdu 610039, China; [EMAIL_ADDRESS] (H.L. ); [EMAIL_ADDRESS] (Z.L. ); [EMAIL_ADDRESS] (Y.S. ); zhangyingyue20163.com (Y.Z. ); wangyue@[EMAIL_ADDRESS] (S.W. ); [EMAIL_ADDRESS] (Q.Z. ); [EMAIL_ADDRESS] (T.C. ); [EMAIL_ADDRESS] (W.X)  
Yingu Zhang  
1 College of Food and Bioengineering, Xilhua University, Chengdu 610039, China; [EMAIL_ADDRESS] (H.L. ); [EMAIL_ADDRESS] (Z.L.L. ); [EMAIL_ADDRESS] (Y.S. ); zhangyingyue20163.com (Y.Z. ); wangyue@[EMAIL_ADDRESS] (S.W. ); [EMAIL_ADDRESS] (Q.Z. ); [EMAIL_ADDRESS] (T.C. ); [EMAIL_ADDRESS] (W.X)  
[PERSON]  
1 College of Food and Bioengineering, Xilhua University, Chengdu 610039, China; [EMAIL_ADDRESS] (H.L. ); [EMAIL_ADDRESS] (Z.L. ); [EMAIL_ADDRESS] (Y.S. ); zhangyingyue20163.com (Y.Z. ); wangyue@[EMAIL_ADDRESS] (S.W. ); [EMAIL_ADDRESS] (Q.Z. ); [EMAIL_ADDRESS] (T.C. ); [EMAIL_ADDRESS] (W.X)  
Yingu Zhang  
1 College of Food and Bioengineering, Xilhua University, Chengdu 610039, China; [EMAIL_ADDRESS] (H.L. ); [EMAIL_ADDRESS] (Z.L. ); [EMAIL_ADDRESS] (Y.S. ); zhangyingyue20163.com (Y.  
Citrus bergamia, Citrus delicious, Montanoa quadrangularis, Juniperus oxycedrus, Citrus unshuit, and Bursera gravelens_[9; 10], and excellent bioactivity has been considered by researchers as a potential sustainable natural active compound [11; 12]. Limonene (1-methyl-4-isopropylcyclohex-1-ene), also known as dipentene, is a natural monocyclic monoterpene that is a colorless liquid with two optical isomers: dextrorotatory D or (+) limonene and levorotatory L or (-) limonene and a racemic mixture (DL-limonene), which have different bioactivities, which may be attributed to the fact that different spatial structures result in different affinities for the active site [13; 14]. Limonene in natural plant essential oils is mainly dominated by D-limonene, which is widely found in the peels of citrus and other fruits as a plant biomarker volatile organic compound with a content of up to 80% or more [15], whereas L-limonene is found in _Cymbopogan nardus_ and _Cymbopogan citratus_, with a content of about 3% [16]; therefore, D-limonene has been extensively studied compared to L-limonene, so this paper will mainly describe the current status of D-limonene research but, in some studies, the authors did not specify the configuration of limonene. It is classified as \"generally recognized as safe\" (GRAS) by the U.S. Food and Drug Administration and is widely used in the food and cosmetic industries [13]. Additionally, D-limonene also has analgesic, anti-inflammatory [17; 18], antioxidant [19], neuroprotective [20], and antimicrobial [21] effects and has hence received extensive attention from researchers. In recent years, research on the practical applications of D-limonene has continued; however, despite its proven bioactivity, its hydrophobicity, volatility, and sensitivity to heat, light, oxygen, and moisture are affected by environmental factors (e.g., oxygen, light, and temperature) when applied directly to food systems and its oxidation gives off unpleasant odors, which, together with its own strong aromatic odor, can interfere with the sensory properties of the food to which they are added [22], which limits its application in food [23; 24]. Currently, researchers are improving the physicochemical properties and bioactivity of D-limonene by producing new materials, such as nanoemulsions and nanofilms, through encapsulation and other techniques, and applying them in practical applications [25]. For instance, nanoemulsions of sodium casenate and D-limonene in specific ratios were generated using high-pressure homogenization, which significantly improved preservation and thermal stability.