NIR Spectroscopy with Chemometric Analysis Allows One to Distinguish Cinnamon from Spent Cinnamon and Cassia

Reviewed: Shawky E, Selim DA. Rapid authentication and quality evaluation of Cinnamomum verum powder using near-infrared spectroscopy and multivariate analysis. Planta Med. 2018;84(18):1380-1387.

Keywords: Adulteration, cassia, Cinnamomum aromaticum, Cinnamomum verum, cinnamon, near-infrared spectroscopy

Cinnamon (Cinnamomum verum, syn. C. zeylanicum) has been used as a spice for thousands of years. In addition to C. verum, the American Spice Trade Association allows other Cinnamomum species to be traded as cinnamon, such as cassia (C. aromaticum, syn. C. cassia), Saigon cinnamon (C. loureiroi), and Indonesian cinnamon (C. burmannii). In traditional herbal medicine, cinnamon is used for gastrointestinal complaints, such as mild cases of spasms, flatulence, or diarrhea,¹ among other indications. Modern research suggests that cinnamon may also be beneficial as adjuvant treatment for glycemic control. Much of the clinical research has been carried out with cassia rather than cinnamon,^2,3 although there are a number of clinical investigations where the exact composition was poorly defined, and the name of species used for the treatment was not provided.⁴ The labeling regulations for dietary supplements in the United States require that common names are consistent with those listed in the American Herbal Products Associations Herbs of Commerce (HOC), which includes cassia, camphor (C. camphora), Saigon cinnamon, Indian cassia (C. tamala), and cinnamon as the Cinnamomum species in the herb trade.⁵ According to HOC, the common name “cinnamon” can only be applied to C. verum, while the common name “cassia” can only be applied to C. aromaticum. Dietary supplement manufacturers have to ensure that they have a means of distinguishing among these species. The bark of the various cinnamon species reportedly can be distinguished morphologically when in stick form based on the way the bark curls,^4,6 but species determination of powdered cinnamon is more challenging, and is usually done by chemical analysis.

The interchangeable use of different Cinnamomum spp. as a spice is well-known. Similarly, it is reasonable to believe that several species are used in food supplements labeled as “cinnamon”. However, the number of Cinnamomum species that can be used as herbal medicines is limited, with national pharmacopoeias describing which species is acceptable. And while some manufacturers may regard the therapeutic benefits of the species in trade as equal, and thus use them interchangeably, Shawky and Selim suggest that cinnamon are also substituted/mixed with cassia for financial gain. Such practices have been reported, e.g., in India, when a study in 2014 found that seven out of 10 cinnamon market samples were actually made from cassia.⁷ Another problem with the quality of cinnamon in trade is the sale of spent cinnamon bark (cinnamon bark of which the essential oil has been removed). The goal of this research project was to develop a quick and economical analytical method to distinguish among cinnamon bark, spent cinnamon bark, and cassia bark, and to detect admixture of spent cinnamon or cassia to authentic cinnamon. For this purpose, 27 botanically authenticated samples of each cinnamon and cassia bark were ground into a fine powder and analyzed by near infrared (NIR) spectroscopy. Spent cinnamon bark was obtained by exhaustive distillation and subsequent drying of nine cinnamon bark samples.

In order to evaluate whether mixtures could be differentiated from cinnamon bark material and if the NIR spectroscopy allowed quantitative measurements, binary cinnamon-cassia, and cinnamon-spent cinnamon mixtures were made in 5% increments, starting with 5% up to 95% adulterant. The spectral data were subjected to multivariate statistics, using principal component analysis (PCA), soft independent modeling by class analogy (SIMCA), and partial least square (PLS) regression modeling. PCA and SIMCA both clustered the spent cinnamon, cassia, and the cinnamon-adulterant mixtures separately from cinnamon. The PLS regression model was used for quantitative prediction of the adulterant concentration in binary mixtures with cinnamon, and yielded good correlations between the predicted data and the actual data.

Comment: Species determination of cinnamon has been a challenge for many in the dietary supplement industry. Methods to differentiate among the species include the comparison of the essential oil fingerprints.^4,8 In addition, the concentrations of coumarin and phenylpropanes (e.g., cinnamaldehyde, cinnamic acid, and eugenol) may be useful to discriminate among the species. Cinnamon has been shown to contain lower amounts of coumarin than the other species, but higher concentrations of eugenol.^9,10 Finally, Chen et al. presented a flow-injection mass spectrometric (FIMS) approach to distinguish among the four species. Based on the PCA loadings plot, the proanthocyanidins (A type in C. verum and C. burmannii; B type in C. aromaticum and C. loureiroi), cinnamaldehyde and coumarin were among the main compounds responsible for separating the species into distinct clusters.¹¹ The NIR method provides an economic alternative to the mass spectrometric techniques, and is sensitive enough to detect adulteration with cassia or spent cinnamon bark at low concentrations (< 2%). Further work is needed to determine if Saigon and Indonesian cinnamon are as easily differentiated from cinnamon as cassia by NIR spectroscopy.

References

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