Non-destructive prediction of pH and total soluble solids of lime [Citrus × aurantifolia (Cristm.) Swinge] by visible and near-infrared spectroscopy

The non-destructive visible and near-infrared spectroscopy (Vis/NIRS) technique is well suited for evaluating various internal quality indices of fruits quickly and accurately. The objective of this study was to evaluate the relationships between Vis/NIR measurements and the internal quality indices of lime, including pH and total soluble solids (TSS, °Brix). For this experiment, reflectance measurement in the 400-2500 nm range was done on 140 samples for pH and 117 samples for TSS. Partial least square (PLS) regression was used to establish the calibration models. First-order derivative and multiplicative scatter correction spectral pretreatments were used to develop calibration models for pH and TSS, respectively. The correlation coefficient (R) and the root mean square error of prediction (RMSEP) from the calibration model for pH were 0.95 and 0.06. The corresponding values for TSS were 0.81 and 0.24 °Brix, respectively. The results showed that Vis/NIRS measurements in the spectral range 400-2500 nm could be used to access pH and TSS of lime.