Maturity evaluation model of tangerine based on spectral index

Based on the spectral analysis, we explored a rapid nondestructive evaluation method for maturity of tangerine and estabilizhed a evaluation model. The data of weight, transverse and longitudinal diameter, chlorophyll, color difference, soluble solids(SSC), acidity(TA) and near infrared spectra were collected from 300 tangerines as experimental samples of 6 different picking time from September to November in 2016. The chlorophyll, chlorophyll/SSC and chlorophyll/solid acid ratio were screened out as the evaluation index of maturity of tangerine by comparing and analyzing the average value and deviation of the above parameters. By using spectral coefficients of variation to analyze the characteristics of the spectra, four characteristic wavelengths of 649, 724, 672, and 1 100 nm were selected. The optimal spectral indexes were obtained by linear combination and correlation analysis of these wavelengths. Then, taking 225 samples as model sets and 75 samples as prediction sets, multiple linear regression(MLR) analysis was conducted for both maturity index and spectral index. By comparison, the prediction model based on chlorophyll as the maturity index was the most accurate, and the correlation coefficient between modeling and prediction was 0.98 and 0.96 respectively. The root mean square error of modeling(RMSEC) and root mean square error of prediction(RMSEP) were 0.49 and 0.59, and the modeling and forecast deviations were -6.1×10^-8 and -0.014, respectively. The results showed that the spectral index can be used to conveniently and accurately evaluate the maturity of tangerine, which provided a theoretical basis for the subsequent development of low-cost maturity-measuring instruments.