Table 1.
Selected spectra intervals by Si-PLS algorithm and their corresponding bonds
| Component | Spectra interval/cm−1 | Corresponding bonds |
|---|---|---|
| Water extracts | 11,359.138–10,796.002 | O–H second overtone and C–H third overtone |
| 6823.197–6260.061 | C–H first overtone | |
| 4559.083–3999.805 | C–H and C–H combinations and C–H and C–C combinations | |
| Tea polyphenol | 10,364.008–9835.586 | N–H second overtone |
| 8234.893–7706.471 | C–H first overtone | |
| 4524.370–3999.805 | C–H and C–H combinations | |
| Free amino acids | 10,225.152–9662.017 | N–H second overtone |
| 8524.174–7961.039 | –CH=CH second overtone | |
| 7957.182–7394.046 | First overtone of C–H combinations | |
| 4559.08–3999.805 | C–H and C–H combinations and C–H and C–C combinations | |
| Caffeine | 7390.189–6827.054 | N–H first overtone |
| 6256.204–5693.068 | C–H first overtone and S–H first overtone | |
| 4559.083–3999.805 | C–H + C–H combinations and C–H and C–C combinations | |
| Total catechins | 9091.167–8528.032 | C–H second overtone |
| 6256.204–5693.068 | C–H first overtone and S–H first overtone | |
| 4559.083–3999.805 | C–H and C–H combinations and C–H and C–C combinations | |
| TF2A | 10,055.440–9449.877 | N–H second overtone |
| 5812.638–5210.932 | C=O stretch second overtone | |
| 4601.511–3999.805 | C–H and C–H combinations, C–H and C–C combinations, N–H and O–H combinations | |
| TF2B | 9658.160–9095.024 | Water absorption |
| 8524.174–7961.039 | –CH=CH second overtone | |
| 5689.211–5126.076 | O–H combination and C–H first overtone | |
| 4559.083–3999.805 | C–H and C–H combinations and C–H and C–C combinations | |
| Theaflavins | 11,359.138–10,796.002 | O–H second overtone and C–H third overtone |
| 10,792.145–10,460.435 | Water absorption | |
| 4559.083–3999.805 | C–H and C–C combinations |
TF2A Theaflavin-3-gallate, TF2B theaflavin-3′-gallate (Cai et al. 2015)