The applicability of NIR spectroscopic technique to determine
the soluble solids content and titratable acidity was tested in three
fruits with different characteristics (passion fruit, tomato and apricot).
The calibration and prediction performance of PLS models
developed with different spectral regions and pretreatment methods
was also investigated. The analysis of the best models shows
that the physical features of the fruit directly affect the results.
The low correlation values for passion fruit were attributed to
the low penetration of infrared radiation due the thick skin of
the fruit. For tomatoes, internal characteristics (heterogeneity)
and high water contents led to weak correlations. On the other
hand, good and robust prediction results were observed for apricot,
which is a fruit with thin skin and homogeneous pulp.
From the results obtained in this work, it can be pointed out
that NIR spectroscopy can be used to predict the soluble solids content
and titratable acidity with excellent accuracy in intact homogeneous
fruits, as apricot. However, a poor performance was
obtained to intact passion fruit and tomato, where NIR was not
adequate to establish quality traits due to the physical structure
of these species. Therefore, it is worthwhile to note that there are
specific limitations to each fruit type, as observed for passion fruit
and tomato, that should be considered in NIR spectroscopy
applications.