Cinnamomum zeylanicum: Morphology, Antioxidant Properties and Bioactive Compounds

Cinnamomum zeylanicum is one of the oldest spices used for culinary purposes in Asian countries. Its extracts have demonstrated a positive impact on controlling the progression of disease pathologies due to antioxidant, anti-inflammatory, antimicrobial, anticancer, anti-mutagenic, anti-tyrosinase and antidiabetic characteristics. C. zeylanicum also has its unique variations which makes it necessary to distinguish it from other species of cinnamon. Phenolic compounds such as cinnamaldehyde, eugenol, carvacrol, cinnamic acetate and thymol are the main compounds that can be found in essential oils of C. zeylanicum. However, cinnamaldehyde and eugenol act as the main bioactive antioxidant compounds found in C. zeylanicum because of their active functional groups in the structures. There are many examples of the use of C. zeylanicum extracts for medicinal purposes, specifically cinnamon metabolite proanthocyanidins which suppress inflammatory compounds and help pathways such as insulin signaling. Moreover, the bioactive compounds in essential oils of this plant are used against many pathogenic (including food-borne) and spoilage bacteria.


Introduction
Cinnamomum zeylanicum (family Lauraceae), known as 'Ceylon cinnamon' or 'true cinnamon', grows as an ever-green tree native to Sri Lanka (earlier Ceylon), and India including other regions of tropical Indochina and Madagascar (Figure 1). This is one of the oldest traditional spice species used for culinary purposes in South Asian countries [1,2]. Additionally, according to toponymical and historical evidence, C. zeylanicum has been used for medicinal purposes since the establishment of Aryan settlements in the Anuradhapura kingdom [3]. Moreover, the indigenous species of Ceylon cinnamon has been used in the Ayurveda system of Sri Lanka [3,4]. Ethnopharmacological studies show that

Morphological features of Cinnamomum zeylanicum
C. zeylanicum has its unique variations which are quite useful in distinguishing it from other species of cinnamon. It is generally grown in loamy, lateritic, and Cinnamomum zeylanicum: Morphology, Antioxidant Properties and Bioactive Compounds DOI: http://dx.doi.org /10.5772/intechopen.97492 silver sand soil and can grow up to 12 m in height. The morphological features which enable the identification of the varieties of C. zeylanicum from other species of Cinnamon based on leaf traits are shown in Table 1 [7]. While the deep vein distribution appears to be common to all Cinnamon species, the color change of the

Type of Cinnamon Flower color Arrangement References
Cinnamomum zeylanicum Greenish In panicles [10,13] Cinnamomum cassia White In panicles [13] Cinnamomum burmannii Whitish Yellow In panicles [14] Cinnamomum tamala Yellow In panicles [13]  leaves from red to deep green and a larger size help to distinguish the C. zeylanicum from C. cassia, C. burmannii and C. tamala. The Cinnamon bark of C. zeylanicum is where most of the bioactive compounds exist, and, there are certain traits which help identify the plant, based on bark characteristics which are shown in Table 2 [4,12]. However, it is also shown that the bark of C. zeylanicum in powder form is practically impossible to distinguish from other wild species of cinnamon due to its identical appearance -a character which is often misused by Cinnamon producers for adulteration. In these instances, an analytical method or a microscope is essential for the identification of Ceylon Cinnamon in its powdered form. However, the aroma from C. zeylanicum is more fragrant and exotic than other varieties. Owing to continued exposure to the plant, traditional Cinnamon growers would have the best sense of distinguishing C. zeylanicum from other varieties simply based on the aroma of the bark.
Flowers of C. zeylanicum are greenish in color and are arranged in panicles both from the axial or apex [10,13,14]. Variations in the Cinnamon flowers based on the different varieties are shown in Table 3. C. zeylanicum flowers have a noticeable green hue which would set it apart from flowers of other Cinnamon varieties.

Antioxidant properties and beneficial effects
Antioxidants are known as substances or compounds, that delay/stop the oxidation by ceasing the damage caused by free radicals. They are able to easily interact with free radicals by oxidation, and generally, the reaction occurs either in single or multi-step fashion. Antioxidants can also react through single electron transfer, hydrogen atom transfer or by chelating transitional metals. Moreover, antioxidants in the biological systems occur as enzymatic and non-enzymatic forms at both extracellular and intracellular environments [2,15,16]. The balance of free radicals and antioxidant defense mechanisms is critically important in health aspects from the perspective of mitigating oxidative stress [17][18][19][20]. Oxidative stress, which is induced by free radicals, is associated with many chronic diseases such as cancer, osteoporosis, diabetes and coronary heart disease [2,4,16,21]. Reactive oxygen species (ROS) induce oxidative stress and are responsible for the cumulative damage imparted on DNA, lipids, proteins and other molecules, subsequently resulting in even permanent damage [17][18][19]22]. Many spices, fruits and vegetables have already been identified as rich in antioxidant compounds such as polyphenols, vitamins, flavonoids and carotenoids [23][24][25]. Moreover, antioxidant-rich foodstuff are good sources to combat and prevent the incidence of many chronic diseases associated with oxidative stress [23].
C. zeylanicum is rich in phenolic compounds. These compounds and their activities are defined by their structure (reactive benzene rings), which is directly linked with quenching radicals in biological systems [17,22,26]. Cinnamaldehyde, eugenol, carvacrol, cinnamic acetate and thymol are the main phenolic compounds that can be found in essential oils of C. zeylanicum [27,28]. Characterization of phenolic compounds in C. zeylanicum revealed that it can improve hyperlipidemia; possibly by lowering cholesterol production, and suppressing lipid peroxidation [1]. Among the parts used in the C. zeylanicum tree for various medicinal purposes, the bark demonstrated the highest antioxidant activity compared to the leaves and flowers [2]. However, essential oils appear to have the greatest antioxidant activity compared to leaves, bark and extracts from other parts of the plant [18].
Peroxynitrite (ONOO-) is a compound capable of reacting with almost every class of biomolecules due to formation of NO2 • and OH • radicals via degradation. These radicals can promote oxidative damage to blood vessels, skin, heart, lungs, kidney, and brain. Eugenol -a component of the active oils extracted from Cinnamon was found to be effective in preventing peroxynitrite-induced damage in vitro. However, the concentration of eugenol present in active oil extracts differ depending on the Cinnamon variety it was extracted from, with C. zeylanicum activity demonstrating the highest. Therefore, from a pure peroxynitrite inhibitory standpoint, Cinnamon oil extracts with a high eugenol content can be classified as a spice to inhibit the activity of radicals NO2 • and OH • [29].
Besides, many studies have been conducted to assess the antioxidant properties of C. zeylanicum with extractions from different parts of the tree, under both in vitro and in vivo conditions [2,19]. Multiple studies have exposed the total antioxidant capacity and its beneficial results such as a decrease in blood lipid peroxide levels through the improvement of hepatic antioxidant enzyme activities [2,19,25], and lowered risks of male infertility, and inflammatory diseases [17]. A study done with swiss albino mice by using Cinnamon 0.25% and Cardamom 0.5%, orally administered at doses of 100 ml/mouse/day, observed that azoxymethane induced colon carcinogenesis could be significantly controlled by inhibiting lipid peroxidation and enhancing Glutathione-S-transferase (GST) activity in liver and colon [30].
In addition to the health benefits, these antioxidants have been used as a primary additive or preservative especially in food industries to prevent or delay the spoilage of food rich in fats and oils [23] and for enhancement flavor [19]. Nowadays, many food industries are concerned with producing food which is less toxic, have fewer health risks and contain a smaller number of synthetic compounds during processing. Therefore, plant-derived antioxidants, especially those coming from C. zeylanicum, has commanded the attention of manufacturers and consumers [2,26,27]. The natural compounds, which are characterized by their antioxidant properties have shown great potential in terms of their health benefits (Table 4) [22,27]. Additionally, these antioxidant compounds are used as substitutes for the synthetic ones such as butylated hydroxytoluene (BHT) and butylated hydroxy anisole (BHA) [22,27,34]. Studies have also revealed that when C. zeylanicum is used as an antioxidant in food, it enhances antioxidant enzymes and remove the ROS, while decreasing malondialdehyde which is naturally present during situations of elevated oxidative stress [17]. C. zeylanicum compounds appear to withstand severe processing conditions as well, since a study has shown that irradiation -which is used frequently to preserve foods these days, does not affect the antioxidant properties of C. zeylanicum extracts [15]. This indicates its suitability as a food preservative [15,35]. Moreover, C. zeylanicum is used in the pharmaceutical industry as a nutraceutical. It is also used in the essence industries due to its fragrance to produce foods, perfumes and drugs [2,22,23].
In terms of the bioactive antioxidant compounds present in C. zeylanicum, cinnamaldehyde and eugenol act as the main bioactive antioxidant compound because of their active functional groups in the structures [36]. Health benefits of antioxidant compounds present in C. zeylanicum are listed in Table 5.
[38] There are other demonstrated beneficial properties of C. zeylanicum. Acetaminophen is an over-the-counter antipyretic-analgesic drug. It exhibits antiinflammatory properties at therapeutic doses. However, it also causes hepatotoxicity [26] Essential oils Cinnamaldehyde, α-pinene, eugenol, β-caryophyllene, and eucalyptol high inhibitory effect against β-carotene discoloration, suppress lipid oxidation reaction, and as a food preservative. [31] Essential oils Cinnamaldehyde, eugenol and carvacrol As feed additives and potential alternative to antibiotics in poultry industry. [32] Essential oil Cinnamaldehyde and cinnamic acetate inhibition of 2-hexenal oxidation [28] Essential oil Cinnamaldehyde and trans-cinnamaldehyde As a drug in phytotherapy disease treatment. [33] Cinnamon (C. zeylanicum) tea Trans-cinnamaldehyde Decrease blood lipid peroxides, increase antioxidant capacity and total thiol molecules.
Antioxidant compounds of C. zeylanicum products and their properties. and nephrotoxicity at large doses. Trials conducted by supplementing high doses of Cinnamon with acetaminophen in four rat groups discovered that pre-treatment with Cinnamon significantly ameliorated cellular alterations and apoptosis [39]. Tauopathy neurodegeneration is a subset of diseases involving a trademark neurofibrillary tangling. Hyperphosphorylation in the microtubular protein known as tau results in the protein disassociating from the microtubules and forming insoluble aggregates. These neurofibrillary tangles of tau are believed to be one of the possible central pathologies of Alzheimer's disease. Cinnamon extract was found to effectively inhibit the aggregation of human tau in vitro. The activity was attributed to a proanthocyanidin trimer and cinnamaldehyde. The same study observed that while the Cinnamon extract inhibited the aggregation of tau, not all polyphenols in the Cinnamon extract are active in the inhibitory process. Therefore, the inhibitory activity cannot be linked to the general antioxidant properties of the extract. However, the studies were performed in vitro, raising concerns about the bioavailability of compounds. Regardless, this study has set the stage and qualified Cinnamon extract for additional testing in clinical trials [40].
Cinnamon extract also exhibited significant gastroprotective effects in a study performed with Wistar albino rats. Gastric lesions were induced via an orally administered indomethacin solution. A Cinnamon suspension was administered 30 min prior to the oral indomethacin, and the animals were sacrificed 6 hours after the treatment. The results found a significant decrease in basal gastric acid secretion and ulcer protective effects across a range of models [41].
Among the bioactive constitutes of C. zeylanicum, cinnamaldehyde and transcinnamaldehyde are considered as the major compounds, especially concerning anti-tyrosinase activity [17]. The spicy and fragrance characters of C. zeylanicum is mainly due to cinnamaldehyde [23]. Based on the richness of bioactive compounds and its medicinal properties, C. zeylanicum is used traditionally to provide aroma and essence compounds. It is also used as an antioxidant, anti-inflammatory, anti-hyperglycemic, anti-lipidemic, antidiabetic, anticancer, antitumor, anthelmintic, anti-aflatoxigenic, antifungal and antimicrobial agent medicinally [1,29,32,[43][44][45][46][47]. There are many examples of its use for medicinal purposes such as Cinnamon metabolite proanthocyanidins which suppresses inflammatory compounds helping pathways such as insulin signaling. Moreover, essential oil bioactive compounds are used against many pathogenic (including food-borne) and spoilage bacteria [17,31,46].

Conclusion
Based on the evidence presented above, it is only pertinent to identify C. zeylanicum as a potent disease-preventing herb due to its superior antioxidant power. While most of the bioactive compounds responsible for this functional property have been isolated and identified, it is evident that the compounds vary with the variety of the plant, environmental conditions as well as the analytical method used for the characterization process. Thus, it is inevitable that more potent antioxidant compounds can be discovered in C. zeylanicum. Even though currently considered as a spice and a traditional medicinal herb, C. zeylanicum has the potential to serve as the source for generating compounds for clinical trials for further evaluation of efficacy and ability to prevent specific diseases.

Antioxidant compounds Reference
Root Bark • Camper [23,36] Flowers and fruits and in lower amounts in buds  © 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.