Assessing the effects of mechanical damage on optical properties of strawberries in the 950-1650 nm range

To investigate the effect mechanism of early damage on optical properties of strawberries, the optical parameters, internal qualities and microstructure parameters of bruised samples and intact ones were acquired and quantitatively analyzed. The results showed that the soluble solids content increased with damage time, while the moisture content decreased. Firmness showed no difference between intact and bruised samples. The cell circularity (Cc) initially decreased, then slightly increased over damage time. The average cell diameter (Davg) increased with longer damage durations, and the average values of cell wall thickness (Tcw) decreased with longer damage durations. The absorption coefficient (mu alpha) values of bruised samples were higher than the intact ones at 970 nm and 1190 nm. For reduced scattering coefficient (mu ' s), at 970 nm and 1190 nm, differences were observed between intact strawberries and bruised samples subjected to three different durations of damage. The average R values of mu ' s with Cc, Tcw and Davg were 0.79, 0.93 and -0.93, respectively, confirming a strong correlation of mu ' s with cell diameter and cell wall thickness. The support vector machine classification model built based on mu alpha spectra had better performance than that based on mu ' sspectra, and the model based on combinations of mu alpha and mu ' s (mu eff) exhibited the highest accuracy for both the calibration set and prediction set with accuracies of 96.00% and 92.19%, respectively. The study provides a theoretical basis for detecting latent damaged strawberries based on optical properties.