Application of near-infrared reflectance spectroscopy to evaluate the lutein and β-carotene in Chinese kale

There are wide ranges of lutein and β-carotene in Chinese kale. This work assessed the capability of near-infrared reflectance spectroscopy (NIRS) to predict the contents of lutein and β-carotene in Chinese kale against HPLC analysis. Compared to other regression methods, the regression of modified partial least squares with math treatments of 2,4,4,1 (where the first number of 2 represents the second derivative of log 1/R, the second of 4 is the gap in data points over which the derivative is calculated, the third and fourth numbers refer to the number of data points used in the first and second smoothing, respectively) showed the best results. The calibration equations of lutein and β-carotene were characterized by the coefficients of determination (RSQ) of 0.983 and 0.982 and standard error of 0.056 and 0.131 mg g−1 DW, respectively. In cross-validation, high 1 minus variance ratio (1 − VR) of 0.955 and 0.966 and standard error of 0.092 and 0.179 mg g−1 DW for lutein and β-carotene were obtained, respectively. In external validations, the RSQ were 0.926 and 0.875 with standard error of 0.131 and 0.367 mg g−1 DW, respectively. These results showed that NIRS could be used for the determination of carotenoids in Chinese kale.