Quantitative visualization of pectin distribution maps of peach fruits

Abstract

Pectin content is an important quality index of fruits, as pectin content undergoes significant changes during the peach ripening process. The commonly used carbazole colorimetry method measures only the total content value of each kind of pectin for each pulp sample and cannot provide distribution maps of the pectin contents for the whole fruit pulp. This work used the hyperspectral imaging technique to quantitatively visualize the distribution maps of pectin contents inside peach pulp at the pixel level. The protopectin contents were well predicted, with the best residual predictive deviation of 2.264, whereas the predictions of the water-soluble pectin and the total pectin contents were not satisfied. On the basis of the best predictive model, the distribution maps of the protopectin contents were quantitatively visualized. A histogram of an example protopectin distribution revealed the existence of a wide range of protopectin contents in peach pulp. Our results show that hyperspectral imaging holds promise as a powerful alternative to the carbazole colorimetry method for measuring the spatial variations in the protopectin distribution inside peach pulp. The distribution maps could be used as a maturity indicator to understand and evaluate the ripening process of peach fruit in depth.

Figure 1

Measured versus predicted pectin contents of the peach pulp by the best models for protopectin (a), water-soluble pectin (b), and total pectin (c).

Figure 2

Examples of the maps of the protopectin distribution inside peach pulp from the fruits with different protopectin contents. The figure at the top right corner shows an example of the histogram of protopectin contents of the pixels within the slice, with a mean content of 2.67 mg/g.

Figure 3

Key steps for the whole procedure.