Table 1. Performance of the PLSR model developed using hyperspectral data with various preprocessing at full wavelength and selected key wavelength
| Wavelengthregion | Pungencycomponent | Pre-processing1) | F2) | Training model (n=315) | Predictionmodel(n=135) |
| Calibration | Cross-validation |
| Offsetc | RMSEC | Rc2 | Offsetcv | RMSECV | Rcv2 | Rp2 |
| Full wavelength | Capsaicin | Raw | 5 | 6.6863 | 33.0606 | 0.9776 | 6.8902 | 34.0150 | 0.9764 | 0.9700 |
| | Normalization | 4 | 7.8969 | 35.9279 | 0.9735 | 8.1336 | 36.7714 | 0.9725 | 0.9631 |
| | SNV | 3 | 9.4645 | 39.3325 | 0.9683 | 9.6388 | 40.0263 | 0.9674 | 0.9531 |
| | MSC | 3 | 9.4645 | 39.3322 | 0.9683 | 9.6324 | 40.0252 | 0.9674 | 0.9531 |
| | SG | 4 | 3.8072 | 24.9469 | 0.9872 | 4.2379 | 25.9852 | 0.9862 | 0.9796 |
| Dihydrocapsaicin | Raw | 6 | 3.7256 | 12.0341 | 0.9769 | 4.0572 | 12.6012 | 0.9748 | 0.9719 |
| | Normalization | 6 | 2.7254 | 10.2924 | 0.9831 | 2.9807 | 11.0459 | 0.9807 | 0.9807 |
| | SNV | 6 | 1.3245 | 7.1757 | 0.9918 | 1.4575 | 7.6669 | 0.9907 | 0.9740 |
| | MSC | 6 | 1.3231 | 7.1711 | 0.9918 | 1.4559 | 7.6572 | 0.9907 | 0.9736 |
| | SG | 5 | 2.7787 | 10.3926 | 0.9828 | 3.2467 | 10.8770 | 0.9813 | 0.9685 |
| Total capsaicinoid | Raw | 6 | 7.6009 | 37.0957 | 0.9835 | 8.0960 | 38.6849 | 0.9821 | 0.9833 |
| | Normalization | 4 | 14.2431 | 50.7809 | 0.9690 | 14.7314 | 51.8528 | 0.9679 | 0.9568 |
| | SNV | 4 | 11.1449 | 44.9196 | 0.9758 | 11.3963 | 46.2343 | 0.9745 | 0.9712 |
| | MSC | 4 | 11.1453 | 44.9193 | 0.9758 | 11.3844 | 46.2284 | 0.9745 | 0.9713 |
| | SG | 3 | 10.6840 | 43.9810 | 0.9768 | 12.1489 | 44.9624 | 0.9759 | 0.9649 |
| Selected key wavelength | Capsaicin | Raw | 5 | 17.7601 | 53.8793 | 0.9405 | 18.0993 | 54.8613 | 0.9387 | 0.9221 |
| | Normalization | 3 | 21.0571 | 58.6663 | 0.9294 | 21.3966 | 59.5285 | 0.9278 | 0.9110 |
| | SNV | 3 | 19.3931 | 56.3022 | 0.9350 | 19.7744 | 57.4230 | 0.9328 | 0.9241 |
| | MSC | 3 | 19.3318 | 56.2113 | 0.9352 | 19.7084 | 57.3285 | 0.9331 | 0.9242 |
| | SG | 3 | 17.6862 | 53.7674 | 0.9407 | 18.2175 | 54.7148 | 0.9390 | 0.9153 |
| Dihydrocapsaicin | Raw | 4 | 10.0777 | 19.7921 | 0.9375 | 10.2481 | 20.1908 | 0.9354 | 0.9351 |
| | Normalization | 3 | 10.4678 | 20.1710 | 0.9351 | 10.6284 | 20.4738 | 0.9336 | 0.9268 |
| | SNV | 5 | 10.8211 | 20.5091 | 0.9329 | 11.3596 | 21.2718 | 0.9283 | 0.9123 |
| | MSC | 5 | 11.0828 | 20.7554 | 0.9313 | 11.6233 | 21.5150 | 0.9266 | 0.9103 |
| | SG | 3 | 9.3156 | 19.0289 | 0.9423 | 9.4943 | 19.3864 | 0.9404 | 0.9355 |
| Total capsaicinoid | Raw | 4 | 28.1112 | 71.3358 | 0.9389 | 28.6070 | 72.6496 | 0.9370 | 0.9261 |
| | Normalization | 3 | 32.2657 | 76.4280 | 0.9298 | 32.7568 | 77.5534 | 0.9282 | 0.9158 |
| | SNV | 5 | 25.1292 | 67.4507 | 0.9453 | 26.2636 | 69.9567 | 0.9416 | 0.9354 |
| | MSC | 3 | 35.1339 | 79.7534 | 0.9236 | 35.9736 | 81.4185 | 0.9209 | 0.9157 |
| | SG | 3 | 26.4502 | 69.2007 | 0.9425 | 27.1553 | 70.3840 | 0.9409 | 0.9235 |
SNV, standard normal variate; MSC, multiplicative scatter correction; SG, Savitzky-Golay first derivative.
F, factor; RMSEC, root mean square errors of calibration; Rc2, correlation coefficient of the calibration; RMSECV, root mean square errors of validation; Rcv2, correlation coefficient of the full cross validation; Rp2, correlation coefficient of the prediction.