Assessing sugar composition and tissue structure indices of ‘Korla’ pear cortex using bulk optical properties in the 500–1500 nm

Optical measurement of fruit quality can provide the specific insights into the light absorption (μa) of chemical compositions and the multiple scattering (μs′) by structured tissues, and contributes to their precise evaluation. This work comprehensively explored the bulk optical properties (BOPs) in the wavelength range of 600–1500 nm related to the soluble sugars, pectin constitution and microstructural features (area, perimeter, Feret’s diameter, cell roundness, cell solidity and intercellular space) of ‘Korla’ pear cortex during post-harvest storage. The high correlation between μa values around 980 nm and 1 485 nm and total sugars and sucrose contents were observed with the r values from 0.74 to 0.99. The μs′ of pear tissues were positively corelated to the firmness, cell microstructure parameters in cortex (area, perimeter, Feret’s diameter and solidity), whereas negatively correlated to their cell roundness and intercellular properties. Besides, the partial least squares regression models based on the featured BOPs of pear cortex successfully predicted the total sugars and sucrose contents with the determination coefficients (Rp2) from 0.73 to 0.91. Further, the combined BOPs feature models based on the first component (PC1) scores of BOPs provide excellent prediction of firmness (Rp2 = 0.90) and acid soluble pectin (Rp2 = 0.93). Accordingly, this study indicated the optical properties have the possibility to present the sugar composition, firmness, pectin and microstructural characteristics of pear tissues.