Relationship between optical properties and internal quality of Orah Mandarins during storage

The optical properties [absorption coefficient (μ_a) and reduced scattering coefficient (μ'_s)] and internal qualities [moisture content (MC), and soluble solids content (SSC)] of Orah mandarin stored at 20 °C for 0-6 days were determined and and the relationship between the optical properties and different quality was explored. The SSC of Orah mandarin initially increased and then decreased, which was due to the phenomenon of low temperature saccharification. The MC remained relatively stable with a slight increase. The pulp tissue absorption coefficient (μ_a) has two absorption peaks at 500 nm and 980 nm, respectively associated with pigments and water. The exocarp tissue has an additional absorption peak at 500 nm related to color, while endocarp tissue only has one absorption peak at 980 nm related to water. The μ_a spectra showed significant correlations with MC and SSC. Partial Least Squares Regression (PLSR) models for predicting the SSC and MC of Orah mandarins were established based on μ_a and μ'_s spectra. The results showed that the prediction model based on μ_a spectra had the best performance. The Correlation Coefficient of Prediction (Rp) and Root Mean Square Error of Prediction (RMSEP) for SSC were 0.921 and 0.549, respectively; for MC, Rp and RMSEP were 0.906 and 0.636 respectively. These results indicate the potential of using the optical properties of Orah mandarins to predict internal quality.