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- Sceletium (Sceletium tortuosum)
- Sceletium crassicaule
- Hyperspectral Imaging
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Date:
03-31-2014 | HC# 111353-493
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Re: Use of Hyperspectral Imaging to Accurately Differentiate and Identify Related Species
Shikanga
EA, Viljoen AM, Vermaak I, Combrinck S. A novel approach in herbal quality control
using hyperspectral imaging: discriminating between Sceletium tortuosum and Sceletium
crassicaule. Phytochem Anal.
2013;24(6):550-555. doi: 10.1002/pca.2431.
Sceletium
(kanna; Sceletium tortuosum) is a
succulent shrub native to South Africa. It has become popular for its
adaptogenic properties and for use in treating psychological, psychiatric, and
inflammatory conditions. Increase in demand has prompted large plantations of S. tortuosum to be grown in South
Africa. S. tortuosum contains the
psychoactive compounds mesembrine, mesembrenol, mesembranol, and mesembrenone. However,
S. tortuosum looks very similar to
the related species S. crassicaule. The
geographical range of these 2 species in the wild is overlapping and both
contain 4 psychoactive alkaloids of interest. Quality control is needed to
ensure that commercial products contain authentic S. tortuosum. The purpose of this in vitro study was to evaluate a
novel quality control tool (hyperspectral imaging [HSI]) for authentication of
botanical identity.
Aerial
parts of S. tortuosum and S. crassicaule plants were collected
from various localities in the Cape region of South Africa in October 2009. The
S. tortuosum samples were collected
from different localities, while S.
crassicaule samples were collected from one locality because it has a more
limited distribution. Voucher specimens for each shrub sampled were retained.
From the collections, 5 S. tortuosum
samples, each representative of 1 of the 5 identified chemotypes, and 5 S. crassicaule samples were selected for
the analyses. The aerial parts were dried, pulverized, and a sub-sample of each
was extracted for chemical profiling using ultrahigh-performance liquid
chromatography (UPLC). The powdered samples were analyzed using shortwave
infrared HSI, an imaging technique that collects and processes information
across a vast span of the electromagnetic spectrum and divides it into multiple
bands. Objects leave unique fingerprints or magnetic spectra which can be used
for identification.
The
UPLC results show that the alkaloid profiles of specimens of both species were variable.
This is in agreement with another study that used a different technique and
demonstrated intra- and inter-population variations in mesembrine-type
alkaloids. Because of this variability, the UPLC method was not adequate for distinguishing
S. tortuosum from S. crassicaule specimens despite the
fact that chromatographic methods are widely accepted for fingerprinting or
profiling of secondary metabolites in plants. HSI demonstrated that the
reflectance intensities of the S.
tortuosum spectra were higher than those for S. crassicaule for each wavelength investigated. This difference enables
the species to be differentiated.
The
authors conclude that HSI can be used to accurately classify a sample as S. tortuosum or S. crassicaule. The HSI method is a non-destructive and time-saving
technique with potential application for on-line quality monitoring of S. tortuosum raw materials. HSI is
increasingly being used in the food processing industry to rapidly detect
foreign material and defective raw materials, so it is not a highly unusual
technique. The article does not address the issues surrounding intra- and inter-population
variations in the total alkaloid content and alkaloid composition of mesembrine-type
alkaloids.
—Heather S. Oliff,
PhD
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