Fourier-transform infrared (FT-IR) and horizontal attenuated total reflectance (HATR) techniques are used to obtain the FT-IR
spectra of the yellow foxtail seed (the seed from Setaria glauca (L. Beauv), the giant foxtail seed (the seed from Setaria
faberii Herrum), and the green foxtail seed (the seed from Setaria viridis (L.) Beauv). The similar FT-IR features among these
three types of seeds are extracted by using continuous wavelet transform (CWT). The decomposition levels 11, 13, and 15 are
used to extract the feature vectors, which are used to train the artificial neural network (ANN). The trained neural network
is used to classify the seeds. The seed samples are collected from different places around the country. With 180 testing samples,
we could more effectively identify the sibling plants — yellow foxtail seed, giant foxtail seed, and green foxtail seed —
by FT-IR with continuous wavelet feature extraction (CWFE) and ANN classification.
Phytotaxonomy is the oldest and the most synthetic branch of plant science. The classical plant classification is based upon
the feature of the plant's exterior appearance and the interior dissection and is quite limited and artificial. Combining
the classic method with a plant's spore-pollen, geographical distribution, and paleobiology simplifies further studies on
the relationship of species identification and plant evolution.
In modern-day science, many different scientific disciplines interact, and new interdisciplinary fields are formed. A new
field of study called phytochemistry systematics was created by the interaction of chemistry and botany. This new field provides
a theoretical foundation for studying and exploiting a plant's systmetic development, utilizing the resource of plants, and
seeking the industrial raw material (1). The chemistry classification for plants is based upon the difference between the
chemical composition in the plant's secondary metabolism (such as saccharide, glucoside, flavonoid, plant alkaloid, terpene,
volatile oil, and tannin) and macromolecule with biological information (such as DNA, RNA, and protein). Currently, the techniques
of chromatography, spectroscopic methodology, and immunology are used in the chemistry classification.
Fourier-transform infrared (FT-IR) spectroscopy can provide all the information about compositional system materials. Different
monoids of plants have different chemical composition and FT-IR spectra, so we can use FT-IR to classify different plants
(2). But FT-IR analysis cannot be used in many areas where fast and accurate classification is needed. A current trend in
instrument analysis is the use of chemometrics to achieve a fast and accurate complex systems analysis and classification
(3–5). Wavelet transform is a more effective signal processing method than the Fourier transform and plays an important role in signal
analysis and feature extraction (6–8). In wavelet multiresolution analysis, wavelet decomposition coefficients of each level
are different for the same characterization of the signal. So the wavelet decomposition coefficients can be considered to
form the feature vector of the signal characteristics. Because only a few coefficients are needed to reflect on the absorption
peaks of spectra, it is one of the more effective chemometrics analysis methods (4).
Artificial neural networks (ANNs) have high intelligence and are used widely. Their calculation is simple and the prediction
is accurate for nonlinear issues (9–12). It is also one of the chemometrics methods to be used in classification or identification.
This article focuses on the classification of three sibling plants, the yellow foxtail seed, the giant foxtail seed, and the
green foxtail seed. These three plants are difficult to distinguish by traditional phytotaxonomy. This study uses FT-IR and
horizontal attenuated total reflectance (HATR) techniques. The feature vectors, which represent spectral characteristics of
the FT-IR, are extracted by using continuous wavelet multiresolution analysis methods. An artificial neural network is used
to classify the sibling plants.
Experimental
Materials
The yellow foxtail seed is the mature, dry seed of Setaria glauca (L.) Beauv that belongs to gramineae. The giant foxtail seed is the mature, dry seed of Setaria faberii Herrum that belongs to gramineae. The green foxtail seed is the mature, dry seed of Setaria viridis (L.) Beauv that belongs to gramineae. The samples were collected from Jinhua of Zhejiang, Jiujiang of Jiangxi, and Beibei
of Chongqing in China in October 2006. All samples were ground to fine powder in agate mortars to 200 mesh respectively and
were stored at the Department of Botany of Zhejiang Normal University in China.
Apparatus
A Nicolet (Madison, Wisconsin) NEXUS 670 FT-IR Spectrometer, equipped with a temperature-stabilized deuterated tryglycine
sulfate (DGTS) detector and a single-bounce HATR accessory. The spectral range is 4000–650 cm–1 with a resolution of 2 cm–1 , and the cumulative scan number is 64.
