Assessment of Glucosinolates in Chinese Kale by Near-Infrared Spectroscopy

Figures & data

Figure 1 General structure of glucosinolates.

Figure 2 HPLC chromatogram of glucosinolates. (a) Internal standard TRO. (b) Glucosinolates in a sample.

Figure 3 Frequency distribution plots (μmol g dw⁻¹). (a) Total glucosinolates. (b) Progoitrin. (c) Sinigrin. (d) Glucoraphanin. (e) Gluconapin. (f) 4-Hydroxyglucobrassicin. (g) Glucobrassicin. (h) 4-Methoxyglucobrassicin. (i) Neoglucobrassicin.

Figure 4 Raw spectra (log 1/R) of the samples of Chinese kale used in this study (n = 150) in the range 400 to 2500 nm.

Table 1 NIRS calibration and validation statistics for the different equations developed for glucosinolates

	Calibration						Validation
Glucosinolate	N	Mean	SD	SECV	1-VR	SD/SECV	RSQ	SEP	Slope	Bias
PRO	137	1.42	0.84	0.36	0.69	2.32	0.34	0.51	0.53	−0.10
SIN	141	1.89	1.36	0.55	0.83	2.46	0.86	0.57	0.92	0.10
RAA	142	2.30	1.97	0.62	0.84	3.18	0.67	0.82	0.93	0.03
NAP	142	10.88	5.19	1.87	0.87	2.78	0.82	2.19	0.82	−0.05
4OH	142	0.12	0.12	0.05	0.82	2.70	0.64	0.07	1.02	0.00
GBC	145	2.30	4.68	1.22	0.93	3.84	0.93	1.04	1.00	−0.04
4ME	142	0.14	0.08	0.04	0.71	1.96	0.58	0.05	1.01	0.00
NEO	141	0.80	1.62	0.44	0.86	3.70	0.90	0.39	0.97	0.01
Total-GSL	141	19.85	10.63	2.96	0.92	3.59	0.91	2.87	0.96	−0.29

PRO: progoitrin, SIN: sinigrin, RAA: gluconapin, 4OH: 4-hydroxyglucobrassicin, GBC: glucobrassicin, 4ME: 4-methoxyglucobrassicin, NEO: neoglucobrassicin, Total-GSL: total glucosinolates, N: number of samples for developing calibration equations, SD: standard deviation of the reference data obtained by HPLC, SECV: standard error of cross-validation, 1-VR: coefficient of determination of the cross-validation, SD/SECV: ratio of the standard deviation of the reference chemistry data to the standard error of cross-validation, RSQ: coefficient of determination in prediction, SEP: standard error of prediction.

Figure 5 Second derivative spectra (2, 5, 5, 2; SNV + DT) of the raw optical data in the range 400 to 2500 nm.

Figure 6 Scatter plots (n = 30). (a) Total glucosinolates. (b) Progoitrin. (c) Sinigrin. (d) Glucoraphanin. (e) Gluconapin. (f) 4-Hydroxyglucobrassicin. (g) Glucobrassicin. (h) 4-Methoxyglucobrassicin. (i) Neoglucobrassicin. Abscissa axis: laboratory values of glucosinolates by HPLC (μmol g dw⁻¹); vertical axis: predicted values of glucosinolates by NIRS (μmol g dw⁻¹).