Prediction of total phenolics, ascorbic acid, antioxidant capacities, and total soluble solids of Capsicum annuum L. (bell pepper) juice by FT-MIR and multivariate analysis

The total phenolic content, antioxidant capacity, ascorbic acid content and total soluble solids content of bell pepper (Capsicum annuum L.) juice were predicted by mid-infrared spectroscopy coupled with chemometrics. The juice of one hundred eighty bell peppers of different colors (green, yellow, orange, and red) was analyzed in terms of spectral and concentration information. The calibration models were obtained by using partial least squares algorithm (PLS1) and considering specific spectral regions for each property. The validation was performed with two approaches, cross-validation (CV) and external-validation (EV). For the PLS1 + CV models, 160 samples were used in both the calibration and validation stage. For the PLS1 + EV models, 120 samples were used to calibrate and 40 to validate the model. Moreover, additional samples were used for the prediction stage. The determination coefficient (R-2), the standard error of calibration (SEC), the standard error of prediction (SEP), the standard error of cross-validation (SECV), and the residual predictive deviation (RPD) were evaluated for each property. The R-2 and RPD were 0.934-0.979 and 3.1-5.12, respectively, for the PLS1 + CV models, and 0.820-0.931 and 5.20-6.96, respectively, for the PLS1 + EV models. The proposed models are a green and straightforward methodology to analyze bell peppers juice properties.