## 2 Results and Discussion
### Fingerprinting of Cinnamon NMR Dataset
#### 2.4.3 Quantification of Major Metabolites via \({}^{1}\)H-NMR  
\({}^{1}\)H-NMR was further used to determine absolute levels of identified metabolites in _Cinnamomun_ samples via the integration of a single well-resolved characteristic signal in the NMR spectra. The concentration of the identified metabolites was expressed as ug/mg dry powder, which is shown in Table 2.  
(_E_)-Cinnamaldehyde represented the major metabolite in all authenticated cinnamon samples ranging from 11 to 19 ug/mg. Interestingly, _Z/E_-cinnamamic acid isomers were quantified in all _Cinnamomun_ authenticated species at almost equal ratios showing its higher levels in CA and CI. Regarding commercial products, (_E_)-cinnamaldehyde represented the major cinnamate, followed by cinnamic acid in CP-1, CP-2, and CP-4. (_E_)-cinnamaldehyde showed its highest level at (7.3 and 6.4 ug/mg) in CP-4 and CP-1, respectively. CP-3 showed an absence of cinnates. (_E_)-methoxy cinnamaldehyde was quantified at (11.2 ug/mg) in _C. verum_ and absent in all other authenticated and commercial samples, and this is in agreement with previous results [48]. (_E_)-Cinnamaldehyde dimethyl acetal was quantified in all authenticated cinnamon samples ranging from 6.5-10.1 ug/mg) and absent in all commercial products posing it as an artifact produced during the extraction of cinnamon powder with methanol (Section 3.3) though performed at room temperature. (_E_)-Cinnamaldehyde dimethyl acetal detection is most probably an adduct of cinnamaldehyde produced during the methanol extraction step [44]. However, the absence of such an acetal in commercial products may be attributed to the presence of cinnamaldehyde in these products at a level less than 10 ug/mg. This agrees with a 72 h stability study proving that the formation of cinnamaldehyde dimethyl acetal in methanol solution of cinnamaldehyde depends on the concentration of cinnamaldehyde and is much lower in solution with the concentration of 10 mg/g [49]. Protocatechuic acid, an antioxidant phenolic metabolite, was also detected at a comparable level (4.2 ug/mg) in _C. cassia_ and _C. iners_ and absent in commercial products. Regarding sugars, contributing mainly to the palatability of cinnamon and its nutritional value, glucose (_a_- and _g_-forms) amounted to the major sugar in authenticated samples, followed by fructose. Likewise, sucrose was quantified in _C. cassia_ and _C. iners_ at 5.1 and 3.7 ug/mg, respectively; however, absent in _C. verum_. Glycerol, sweet sugar alcohol, was quantified at maximal level ca. 5 ug/mg in _C. cassia_ and _C. iners_. While _C. cassia_ showed the highest concentration of total sugars at 36.3 ug/mg, followed by _C. iners at 24.4 ug/mg. For commercial products, monosaccharides, i.e., glucose (in its _a_- and _g_-forms) and fructose, were found major in CP-2 and CP-4, albeit sucrose was quantified at maximal level (9.0 ug/mg) in CP-1 and absent in other commercial products. Coumarin, a hepatotoxic metabolite, reached its highest level at 13.8 and 10.4 ug/mg in CI and CA, respectively. However, the CV showed an absence of coumarin, emphasizing its genuineness. Regarding commercial products, coumarin was detected at its higher level in CP-1 at 3.2 ug/mg, while CP-2 and CP-4 at 2.7 and 3.0 ug/mg, respectively, could not be detected in CP-3. These findings are in accordance with the labeled origin being derived from _C. cassia_ and confirming results revealed from VOCs profiling. It is clear from quantitative NMR of commercial products that samples CP-1, CP-2, and CP-4 showed nearly the same pattern of metabolites with almost no significant differences (\(p\leq 0.05\)) among most metabolites, except for (\(E\))-cinnamaldehyde where CP-1 (6.4 \(\mathrm{\SIUnitSymbolMicro\text{mg}}\)) and CP-4 (7.3 \(\mathrm{\SIUnitSymbolMicro\text{mg}}\)/mg) showed significant difference from CP-2 (4.9 \(\mathrm{\SIUnitSymbolMicro\text{mg}}\)/mg) being different from GC/MS results which showed the highest values in CP-2 and CP-4, Table S1.