Rapid Prediction of Steviol Glycosides, Chlorogenic Acids and Moisture in Stevia by Models Based on Near Infrared Diffuse Reflection Spectrometry

Based on near infrared diffuse reflection spectrometry, the models of total steviol glucosides (TSG), rebaudioside A (RA), stevioside (STV), total chlorogenic acids and moisture in stevia combined with partial least square (PLS) method were established. Stevia samples of 500 from different regions were selected, and the data obtained by high performance liquid chromatography (TSG, RA, STV, total chlorogenic acids) and oven drying method (moisture) were used as reference. The models were established combined with near infrared spectra of samples according to the following conditions: 1 TSG model, calibration set of 385, verification set of 97, spectral pretreatments of MSC+1st+ND, spectral range of 4 090.76-7 085.37 cm^-1, and principal factor number of 8; 2 RA model, calibration set of 381, verification set of 94, spectral pretreatments of MSC+2nd+ND, spectral ranges of 4 060.38-6 221.23 cm^-1, 6 769.51-7 401.24 cm^-1, and principal factor number of 7; 3 STV model, calibration set of 386, verification set of 96, spectral pretreatments of MSC+1st+ND, spectral ranges of 4 017.86-4 224.39 cm^-1, 4 370.17-5 172.15 cm^-1, 5 414.95-9 106.22 cm^-1, and principal factor number of 5; 4 total chlorogenic acids model, calibration set of 376, verification set of 95, spectral pretreatments of SNV+1st+SG, spectral ranges of 4 000.21-5 300.00 cm^-1, 5 624.00-6 246.90 cm^-1, 8 746.50-9 373.80 cm^-1, and principal factor number of 12; 5 moisture model, calibration set of 389, verification set of 96, spectral pretreatments of MSC+1st+ND, spectral ranges of 4 072.53-7 553.09 cm^-1, and principal factor number of 8. It was shown that the correlation coefficients of correction, prediction and cross validation for TSG, RA, STV, total chlorogenic acids and moisture models were all greater than 0.800 0. The root mean square errors of correction, prediction and cross validation were less than 0.500. External validation of the models showed that the correlation coefficients between predicted values and determined values for TSG, RA, STV, total chlorogenic acids and moisture were greater than 0.880 0. TSG, RA, STV, total chlorogenic acids and moisture in stevia samples were analyzed by their models, and the intra-day precision (n=6) and inter-day precision (n=6) were in the ranges of 0.54%-2.7% and 1.1%-4.7%, respectively. The models have been applied to the determination of TSG, RA and total chlorogenic acids in stevias from different growth batches at a test base, and the mass fractions of TSG, RA and total chlorogenic acids were in the ranges of 10.40%-13.32%, 4.99%-7.61% and 2.73%-4.07%, respectively, with RSDs (n=12) of the determined values were less than 7.0%.