Evelina, Dalinette and FEM7 were firmer cultivars, especially the
latter two, which were higher in yield, mean and max force compared
to other crunchy cultivars but had lower values for acoustic
properties, indicating that these cultivars were less crunchy. This
result reinforces the fact that differences in apple textural profiles
are not limited to just ‘soft-not crunchy’ and ‘firm-crunchy’ but
also include ‘firm-less crunchy’ and ‘less firm-crunchy’ (Costa
et al., 2011). These results also imply that the acoustic properties
of apple flesh are dependent on its underlying structural mechanical
properties.
Expressed juice was positively correlated (p < 0.05, mean
r = 0.51) to all acoustic properties, with cultivars higher in acoustic
parameters containing more expressed juice (Fig. 2). This correlation
was interpreted as the sound being louder when turgid cell
walls are ruptured due to external pressure (Duizer, 2001). This
result implies that during consumption, some apple cultivars are
perceived as juicy and crunchy due to the rupturing of cells and
expulsion of juice, which in turn causes a higher acoustic pitch during
mastication.