Rapid Prediction of Antioxidant Activity of Coreopsis Tinctoria by Model Established by Near Infrared Spectroscopy with Partial Least Square Regression

Ten batches of Coreopsis tinctoria samples from different origins were naturally dried, crushed, and screened. An aliquot (0.2 g) was taken and mixed with 50 mL of 35% (volume fraction) methanol solution. The mixture was settled overnight, and treated by ultrasonic for 30 min. After suction filtration, the filtrate was collected. The antioxidant activities (reference values) of Coreopsis tinctoria were determined by 1,1-diphenyl-2-picrohydrazyl (DPPH) method and 2,2'-diazepine (3-ethylbenzothiazolin-6-sulfonic acid) diamammonium salt (ABTS) method. The near infrared spectrometer was used to scan the spectra of 100 Coreopsis tinctoria powder samples, and the near infrared integrating sphere diffuse reflection mode was used to collect the spectra. The antioxidant activity model of DPPH was established combined with partial least square regression (PLSR) in the wavebands of 4 767-4 960 cm^-1, 5 153-6 966 cm^-1 and 7 120-8 813 cm^-1 after the original near infrared spectra data were pretreated by standard normal variate (SNV)+continuous wavelet transform (CWT), and the antioxidant activity model of ABTS was established combined with PLSR in the wavebands of 5 153-7 081 cm^-1 and 7 660-8 624 cm^-1 after the original near infrared spectra were pretreated by CWT. The results showed that the root mean square error of cross validation (RMSECV), correlation coefficient (R) and predictive residual value (RPD) of antioxidant activity model of DPPH was 0.772, 0.948 and 3.17, respectively, and those of antioxidant activity model of ABTS were 0.365, 0.884 and 2.52, respectively. The antioxidant activities of DPPH and ABTS of Coreopsis tinctoria samples were predicted by the models, giving results of the predicted values were basically consistent with the reference values, and root mean square error of prediction (RMSEP) of the antioxidant activity model of DPPH was 0.705, and that of the antioxidant activity model of ABTS was 0.377.