Ripeness Assessment of Tomato Fruit by Optical Absorption and Scattering Coefficient Spectra
HUANG Yu-ping1, WANG De-zhen1, ZHOU Hai-yan1, YANG Yu-tu1, CHEN Kun-jie2*
1. College of Mechanical and Electronic Engineering, Nanjing Forestry University, Nanjing 210037, China
2. College of Engineering, Nanjing Agricultural University, Nanjing 210031, China
Abstract：Maturity is one of the most important parameters in determining the picking time and assessing the postharvest quality. As the maturity of tomato fruit advanced, the chlorophyll content decreases, while anthocyanin starts to increase, resulting in color changes for tomato fruit, which suggests color characteristics is closely related to the maturity for tomatoes. The total 600 tomatoes at six maturity stages were used for the test, absorption and reduced scattering coefficients for tomato fruit were extracted by spatially resolved spectroscopy, partial least squares models discriminant analysis (PLSDA) models were built for evaluating tomato maturity. Spatially resolved (SR) spectra for each tomato sample were acquired using a novel spatially resolved spectroscopic system over the spectral region of 550～1 650 nm. Since the 30 fibers in SR probe were arranged in symmetry, each pair of symmetric spectra were averaged, which resulted in 15 relative reflectance spectra covering the light source-detector distances of 1.5～36 mm. Due to strong water absorption beyond 1 300 nm, only 550～1 300 nm was selected for extracting the absorption and reduced scattering coefficients of tomato fruit. Besides，nine SR spectra over the spatial distances from 1.5 to 12.5 mm were actually used to analyze the absorption and reduced scattering properties of tomato fruit in this study, because the signal beyond 12.5 mm was too weak to be useful. And then the values for the absorption and reduced scattering coefficient were obtained by the diffusion approximation equation coupled with a nonlinear inverse algorithm. Chlorophylls content decreases at 675 nm along with the increases of anthocyanin at 560 nm as tomato turns from green to red. The values of the reduced scattering coefficient decreased steadily with the increasing wavelength for all tested tomato samples over the spectral region of 550～1 300 nm. The classification results were compared using μa and μ′s. Besides, tomato maturity stages were evaluated based on surface color and internal color. The results showed the combinations of μa and μ′s could further improve classification results compared with single μa and μ′s spectra, especially μa×μ′s (multiplication of the two parameters wavelength by wavelength)，which presented recognition rate of 78.5% and 85.5% for internal color and surface color, respectively. Better classification results were obtained for three ripeness stages using μa and μ′s and their combinations, and the recognition rates were similar, around 94% for internal and surface color. The research demonstrated the optical absorption and scattering spectra could classify tomato ripeness stages effectively. The research provided a new means for nondestructive detection in agricultural products.
黄玉萍，王德镇，周海燕，杨雨图，陈坤杰. 基于光学吸收和散射系数光谱的番茄成熟度分析方法研究[J]. 光谱学与光谱分析, 2020, 40(11): 3556-3561.
HUANG Yu-ping, WANG De-zhen, ZHOU Hai-yan, YANG Yu-tu, CHEN Kun-jie. Ripeness Assessment of Tomato Fruit by Optical Absorption and Scattering Coefficient Spectra. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2020, 40(11): 3556-3561.
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