Fig. 1. Moisture absorption curve of stevia

Fig. 2. Spectral changes of stevia during moisture absorption
(a): Raw spectra; (b): Multivariate scatter correction spectra;(c): A magnified plot at 1 850~2 050 nm; (d): Second derivative spectra of 1 850~2 050 nm

Fig. 3. Spectra of 55 stevia samples with different RA content
(a): Raw spectra; (b): Spectra after MSC processing

Fig. 4. Scores and loadings of the first two principal components in the combination bands of OH in the moisture absorption process
(a): Scores of the first principal component; (b): Loadings of the first principal component;(c): Scores of the second principal component; (d): Loadings of the second principal component

Fig. 5. Synchronous (1) and asynchronous (2) 2D correlation spectra of the stevia moisture absorption process
The first hour (a1, a2) the middle two hours (b1, b2) and the last hour (c1, c2)

Fig. 6. Schematic diagram of the calculation process of the EPO algorithm
(a): The spectra before EPO correction; (b): The difference spectra of the stevia moisture absorption process;(c): The cross-validation error graph generated by different combinations of c and LVs; (d): The spectra after EPO correction

Fig. 7. (a) LV-RMSECV curve; (b) NIRS quantitative analysis model of RA content in stevia