*3.3. PLSR Results of SSC for Mixed Apple Size*

To verify that apple size differences affect their NIR spectra and lead to poor prediction performance of the developed apple SSC prediction model. The calibration and prediction sets of fruit diameter groups 65–75 mm, 75–85 mm, and 85–95 mm were used as the calibration and prediction sets of the mixed fruit diameter apple prediction model to establish the PLSR of SSC for different apple sizes, and the model effects are shown in Table 2.
