Figure 1.
Inhibition percentage of GRCB solution and sitagliptin.
Figure 2.
Total ion chromatogram of GRCB of Coffea liberica obtained from LC-HRMS analysis.
Table 1.
Major metabolite compounds identified using LC-HRMS analysis.
| No. | Name | Formula | Calc. MW | RT (min) | Area (%) | References |
|---|---|---|---|---|---|---|
| 1 | 1,3,7-Trimethyl-2,3,6,7-tetrahydro-1H-purine-2,6-dione | C8H10N4O2 | 194.080 | 4.027 | 61.344 | Mazzafera et al., 1994 |
| 2 | Methyl isonicotinate | C7H7NO2 | 137.048 | 0.809 | 13.210 | Liu et al., 2009 |
| 3 | 1-Stearoylglycerol | C21H42O4 | 358.307 | 15.438 | 3.910 | Ma et al., 2002 |
| 4 | 4-Hydroxycoumarin | C9H6O3 | 162.032 | 3.712 | 2.356 | Vezzulli et al., 2022 |
| 5 | 3-Hydroxy-2-methylpyridine | C6H7NO | 109.053 | 0.803 | 2.138 | Subarnas et al., 1991 |
| 6 | Maltol | C6H6O3 | 126.032 | 2.245 | 1.922 | Stoffelsma et al., 1968 |
| 7 | Choline | C5H13NO | 103.100 | 0.764 | 1.561 | Shirley & Chapple, 2003 |
| 8 | (1R,3R,4S,5S)-4-{[(2E)-3-(3,4-dihydroxyphenyl)prop-2-enoyl]oxy}-1,3,5-trihydroxycyclohexane-1-carboxylic acid | C16H18O9 | 354.095 | 3.705 | 1.369 | Moreira et al., 2005 |
| 9 | 1-Linoleoyl glycerol | C21H38O4 | 354.276 | 14.165 | 0.887 | Tran et al., 2023 |
| 10 | Picolinic acid | C6H5NO2 | 123.032 | 1.014 | 0.589 | Du et al., 2007 |
| 11 | NP-011220 | C11H18N2O2 | 210.137 | 5.313 | 0.585 | Zhang et al., 2007 |
| 12 | 3-[(19Z)-15,16-dihydroxy-19-dotriaconten-1-yl]-5-methyl-2(5H)-furanone | C37H68O4 | 576.511 | 21.305 | 0.522 | Gleye et al., 2000 |
| 13 | d-(+)-Pyroglutamic acid | C5H7NO3 | 129.043 | 1.053 | 0.512 | Osborne et al., 1994 |
| 14 | Ethyl palmitoleate | C18H34O2 | 282.255 | 15.606 | 0.465 | Ekpendu et al., 1993 |
| 15 | 2,2,6,6-Tetramethyl-1-piperidinol (TEMPO) | C9H19NO | 157.147 | 8.994 | 0.442 | Aprilia et al., 2025 |
| 16 | N,N-dimethylaniline | C8H11N | 121.089 | 1.135 | 0.435 | Thomas & Bassols, 1992 |
| 17 | (1S,3R,4R,5R)-1,3,4-trihydroxy-5-{[(2E)-3-(4-hydroxy-3-methoxyphenyl)prop-2-enoyl]oxy}cyclohexane-1-carboxylic acid | C17H20O9 | 368.111 | 5.053 | 0.428 | Moreira et al., 2005 |
| 18 | Guvacoline | C7H11NO2 | 141.079 | 1.766 | 0.402 | Holdsworth et al., 1998 |
| 19 | 3-Hydroxypyridine | C5H5NO | 95.037 | 0.801 | 0.384 | Miyazawa et al., 1983 |
| 20 | Monoolein | C21H40O4 | 356.292 | 14.781 | 0.362 | Okuyama et al., 2001 |
| 21 | 7-Hydroxy-6-methoxy-2H-chromen-2-one | C10H8O4 | 192.042 | 5.690 | 0.329 | Komissarenko & Kovalev, 1992 |
| 22 | NP-019811 | C6H7NO2 | 125.048 | 1.035 | 0.325 | Zheng et al., 2018 |
| 23 | Sitostenone | C29H48O | 412.370 | 19.156 | 0.282 | Xie et al., 2007 |
| 24 | o-Toluidine | C7H9N | 107.074 | 1.133 | 0.273 | Vitzthum et al., 1975 |
Figure 3.
FTIR spectral profiles of GRCB, starch as an adulterant, and adulterated GRCB. Annotated peaks indicate selected peaks for generating the PCA model.
Figure 4.
Individual plot (a) and variables plot (b) resulting from the principal component analysis.
Figure 5.
AUC-ROC graph (a), individual background plot which was obtained using the maximum distance approach (b), and classification error rate analysis (c) of the partial least-squares discriminant analysis.
Table 2.
FTIR spectral and functional groups identification.
| No | Wavenumbers (cm−1) | Functional groups | Related compounds/materials | References | |
|---|---|---|---|---|---|
| Identified | Literature | ||||
| 1 | 3290 | 3660–2970 | OH (phenol, alcohol, carboxylic acid) | Phenolic compound | Abreu et al., 2020 |
| 2 | 2924 | 2925–2908 | C=O and C–H | Lipid | Sahachairungrueng et al., 2022 |
| 3 | 2854 | 2858 | C–H methyl | Caffeine | Silva et al., 2018 |
| 4 | 1743 | 1745 | Carboxyl linkage derived from xanthine derivatives | Caffeine | Wei-Lung Chou, 2012 |
| 5 | 1643 | 1650–1580 | C=C phenyl ring | Chlorogenic acid isomers | Liang et al., 2016 several indices of browning and subsequent antioxidant values. Principal component analysis was used to interpret the correlations between physiochemical and antioxidant parameters of coffee. CGA isomer content was positively correlated (p < 0.001 Simatupang et al., 2023 |
| 6 | 1149 | 1176–1106 | C–OH cyclohexane | Chlorogenic acid isomers | Abreu et al., 2020 Simatupang et al., 2023 |
| 7 | 1076 | 1077 | C–O–C of hydrogen bonds between starch molecules | Starch | Abdullah et al., 2019 |
| 8 | 999 | 1157–982 | C–O and C–C stretching with COH contributions | Starch | Pozo et al., 2018 |
| 9 | 930 | 920 | C–O–C ring vibration of carbohydrate | Starch | Abdullah et al., 2018 |
| 10 | 860 | 856 | C–O–C ring vibration of carbohydrate | Starch | Abdullah et al., 2018 |