Simultaneous estimation of amylose, resistant, and digestible starch in pea flour by visible and near-infrared reflectance spectroscopy

Figures & data

Figure 1. Visible and near infrared reflectance spectra from scanning pea flour samples by using a miniature fiber optic spectrometer (StellarNet Inc., USA). The X-axis is wavelength (nm) and Y-axis is the reflectance (%).

Table 1. Descriptive statistics of the data sets for amylose, resistant starch, digestible starch, and total starch determined by enzymatic colorimetric assay.

Component	Mean	Range	SD	CV
Amylose (%)	16.50	9.01–66.17	8.57	51.94
Resistant starch (%)	3.85	0.87–11.65	1.93	50.03
Digestible starch (%)	41.96	25.40–86.00	8.45	20.14
Total starch (%)	45.81	30.51–97.16	8.95	19.55

SD: Standard deviation; CV: coefficient of variation calculated as (SD × 100)/mean.

Table 2. Comparison of the PLS models using different data preprocessing procedures.

Preprocessing procedure	RMSEP	R^2p	RMSECV	$R_{\mathrm{c}\mathrm{v}}^2$
Estimation of amylose
Unprocessed	3.58	0.87	2.78	0.92
Normalization	3.46	0.88	2.55	0.93
MSC	3.47	0.88	2.62	0.93
SNV	3.03	0.91	2.48	0.93
S.G. 1st derivative	3.57	0.87	2.54	0.93
Estimation of resistant starch
Unprocessed	3.22	0.18	2.45	0.51
Normalization	3.27	0.15	2.45	0.51
MSC	3.34	0.12	2.08	0.65
SNV	3.30	0.12	2.49	0.50
S.G. 1st derivative	3.01	0.28	2.41	0.53

RMSEP and $R_{\mathrm{p}}^2$ : The root mean square error of prediction and the correspondent coefficient of determination; RMSECV and $R_{\mathrm{c}\mathrm{v}}^2$ : the root mean square error of cross-validation and the correspondent coefficient of determination.

Table 3. Highly correlated wavebands and corresponding correlation coefficients (in parentheses) for estimating amylose, resistant starch, digestible starch, and total starch.

Variables	Highly correlated wavebands (correlation coefficients, R^2)
Amylose	384–417 (0.898–0.908), 453–489 (0.881–0.891), 501–534 (0.825–0.859), 1066–1093 (−0.580 to −0.583), 1243–1426 (−0.582 to −0.592), 1600–1654 (−0.610 to −0.659)
Resistant starch	370–423 (0.605–0.688), 429–498 (0.588–0.596), 510–567 (0.501–0.588), 1084–1096 (−0.337), 1411–1420 (−0.337), 1600–1618 (−0.338 to −0.351)
Digestible starch	402–426 (0.627–0.638), 447–495 (0.628–0.647), 1615–1678 (−0.633 to −0.697), 1774–1838 (−0.638 to −0.675)
Total starch	390–420 (0.801–0.816), 450–468 (0.797–0.809), 474–540 (0.709–0.801), 1348–1420 (−0.622 to −0.640), 1618–1641 (−0.707 to −0.727), 1762–1837 (−0.611 to −0.655)

Table 4. The multiple linear regression models (MLR) and adjusted coefficients of determination (adj. R²) for amylose, resistant starch, digestible starch, and total starch estimation using the most significant vis–NIRS wavebands.

	Wavelength	Multiple linear regression model	Adj. R^2
Amylose	w1–w10: 387, 393, 411, 435, 456, 486, 507, 525, 540, 1630	Amylose = 4.986 + 0.165 × RW1 − 0.168 × RW2 + 0.182 × RW3 − 0.081 × RW4  − 0.083 × RW5 + 0.067 × RW6 − 0.019 × RW7 − 0.016 × RW8 + 0.015 × RW9 − 0.001 × RW10	0.952
RS	w1–w13: 390, 396, 402, 438, 456, 471, 489, 537, 549, 564, 1096, 1612, 1618	RS = − 10.918 + 0.213 × RW1 − 0.293 × RW2 + 0.258 × RW3 − 0.065 × RW4 − 0.142 × RW5  + 0.072 × RW6 + 0.025 × RW7 − 0.03 × RW8 + 0.03 × RW9 − 0.007 × RW10 − 0.002 × RW11 − 0.01 × RW12 + 0.012 × RW13	0.756
DS	w1–w8: 450, 456, 1621, 1645, 1657, 1780, 1792, 1822	DS = 453.142 − 0.082 × RW1 + 0.084 × RW2 − 0.044 × RW3 + 0.066 × RW4 − 0.045 × RW5 + 0.102 × RW6 − 0.092 × RW7 + 0.013 × RW8	0.803
Total starch	w1–w11: 390, 396, 402, 411, 438, 510, 531, 1618, 1780, 1792, 1810	Total starch = 268.891 − 0.288 × RW1 + 0.393 × RW2 − 0.337 × RW3 + 0.308 × RW4  − 0.099 × RW5 + 0.013 × RW6 − 0.006 × RW7 − 0.01 × RW8 + 0.037 × RW9 − 0.037 × RW10 + 0.009 × RW11	0.881

wn: Wavelength; R_wn: the first derivative reflectance spectra value of wn.

RS: Resistant starch; DS: digestible starch

Figure 2. Comparison of the laboratory-measured resistant starch, digestible starch, amylose, and total starch with the vis–NIRS model estimated values.

Table 5. Correlation matrix among resistant starch, digestible starch, amylose, and total starch determined by chemical methods.

	Resistant starch	Digestible starch	Amylose	Total starch
Resistant starch	1
Digestible starch	0.087	1
Amylose	0.719**	0.698**	1
Total starch	0.475**	0.918**	0.903**	1

**Significant at P < 0.01 by two-tailed test.