NIR spectroscopy has been a powerful tool for quality detection
and process control in the agricultural and food industries.
Numerous studies have been reported in recent years on NIR
spectroscopy for fast measurement of SSC and other quality
attributes of apple. In the study of Eisenstecken et al. (2015), an SSC
model was built within the range of 1000–2500 nm, and the SSC
prediction model showed inadequate coefficients of determina-
tion. Additionally, Peirs et al. (2001) and Kumar et al. (2015)
included wavelengths in the visible range to increase the model
accuracy. Moreover, an automatic apple rotation was successfully
applied to improve the determination of quality characteristics
(Schmutzler and Huck, 2014). They obtained SECV values of 0.45%
and 0.46% for the SSC of Pink Lady and Golden Delicious apples,
respectively. Compared to previous investigations, the models
built in this work had an excellent performance. In addition, color
factor has not been considered to compensate quality model.
This work has shown a great potential for obtaining reliable
predictions of SSC of apple, both by SWNIR and LWIR as a
nondestructive tool. Table 2 shows the summary results for SSC
using various calibration methods. Compared with conventional
PLS models, the variable selection procedures and color compensation
method significantly improved the performance of the
final
model. From the results we can conclude that (1) nonlinear models
are superior to linear models; (2) the ICA algorithm has a better
capacity to select variables for modeling; (3) color compensation
may further improve the performance of the
final model. As to the
models developed for SSC, the LWNIR range was slightly better
compared to the SWNIR range. However, no significant differences