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. 2024 May 24;24(11):3362.
doi: 10.3390/s24113362.

Simultaneous Determination of Four Catechins in Black Tea via NIR Spectroscopy and Feature Wavelength Selection: A Novel Approach

Affiliations

Simultaneous Determination of Four Catechins in Black Tea via NIR Spectroscopy and Feature Wavelength Selection: A Novel Approach

Yabing Liu et al. Sensors (Basel). .

Abstract

As a non-destructive, fast, and cost-effective technique, near-infrared (NIR) spectroscopy has been widely used to determine the content of bioactive components in tea. However, due to the similar chemical structures of various catechins in black tea, the NIR spectra of black tea severely overlap in certain bands, causing nonlinear relationships and reducing analytical accuracy. In addition, the number of NIR spectral wavelengths is much larger than that of the modeled samples, and the small-sample learning problem is rather typical. These issues make the use of NIRS to simultaneously determine black tea catechins challenging. To address the above problems, this study innovatively proposed a wavelength selection algorithm based on feature interval combination sensitivity segmentation (FIC-SS). This algorithm extracts wavelengths at both coarse-grained and fine-grained levels, achieving higher accuracy and stability in feature wavelength extraction. On this basis, the study built four simultaneous prediction models for catechins based on extreme learning machines (ELMs), utilizing their powerful nonlinear learning ability and simple model structure to achieve simultaneous and accurate prediction of catechins. The experimental results showed that for the full spectrum, the ELM model has better prediction performance than the partial least squares model for epicatechin (EC), epicatechin gallate (ECG), epigallocatechin (EGC), and epigallocatechin gallate (EGCG). For the feature wavelengths, our proposed FIC-SS-ELM model enjoys higher prediction performance than ELM models based on other wavelength selection algorithms; it can simultaneously and accurately predict the content of EC (Rp2 = 0.91, RMSEP = 0.019), ECG (Rp2 = 0.96, RMSEP = 0.11), EGC (Rp2 = 0.97, RMSEP = 0.15), and EGCG (Rp2 = 0.97, RMSEP = 0.35) in black tea. The results of this study provide a new method for the quantitative determination of the bioactive components of black tea.

Keywords: FIC-SS-ELM; NIRS; black tea; catechin content prediction; wavelength selection.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
The ELM network structure for simultaneous prediction of four catechins in black tea.
Figure 2
Figure 2
Descriptive statistics of four catechins in black tea. (a) Box plot of the EC, ECG, EGC, and EGCG contents; (b) correlation analysis between the EC, ECG, EGC, and EGCG contents.
Figure 3
Figure 3
(a) Raw spectral curves of black tea samples after SG filter; (b) PCA clustering diagram using the first three PCs.
Figure 4
Figure 4
The optimal feature wavelength intervals and variables extracted by four feature wavelength selection algorithms: (a) FIC-SS; (b) MC-UVE; (c) SPA; (d) CARS.
Figure 5
Figure 5
Scatter plots of the FIC-SS-ELM for the prediction of catechins in black tea. (a) EC, (b) ECG, (c) EGC, and (d) EGCG content.

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