Abstract: To understand the optical properties of fruits and their relationships with soluble solids content (SSC) and moisture content, a single integrating sphere system for the measurement of optical properties was established and validated. Furthermore, the absorption coefficient μa and reduced scattering coefficient μ’s of the fruit of the strawberry cultivars ‘Hongyan’, ‘Tianxiang’ and ‘Zhangji’, were measured over the wavelength range of 950–1 650 nm. The relationships of optical properties with SSC and moisture content were analyzed, and partial least squares models to predict SSC and moisture content based on optical properties were established. The results showed that the average relative errors of the system for μa and μ’s were 8.23% and 3.71%, respectively. Over the investigated wavelength range, μa had peaks at 975, 1 197 nm and 1 411 nm, and μ’s generally decreased with increasing wavelength. μa had negative correlation with SSC but positive correlation with moisture content. Moreover, extreme correlation coefficients were observed at the absorption peaks. The models established based on the spectra of μa had the best capability in predicting SSC (rp = 0.815, root mean squares error of prediction (RMSEP) = 1.153%) and moisture content (rp = 0.757, RMSEP = 1.280%), indicating that SSC and moisture content mainly affected the optical absorption property of strawberry fruit, which allowed good prediction of the internal quality of strawberry fruit.

Key words: strawberry; absorption coefficient; reduced scattering coefficient; soluble solids content; moisture content