3.4. Texture trend
Just after baking, Amaretti cookies have a double layer structure,
with a hard crust and a softer inner part, as indicated by a bimodal
curve in Fig. 4, where the higher peaks of the curves represent the
force applied to penetrate the crust of the cookies. The curves
showed similar behaviour during storage, for both samples (data
not shown). The trend of the texture indexes over time is shown in
Table 2. The CON and A15 samples did not differ significantly in the
initial values of the inner part and bottom crust hardness, while
they differed in bottom crust thickness. Starting from 30 days and
throughout the storage period, CON cookies had significantly
higher values of the inner part than A15 cookies. This can surely
be attributed to the higher moisture content of the A15 samples
than the CON ones (Fig. 2), due to water-binding properties of the
added ovine whey powder. In fact, the data analysis showed
a strong correlation between moisture content and hardness of the
internal part; Pearson’s correlation between variables was 0.953
and 0.743 in CON and A15 samples, respectively (Fig. 5). Hardness
of the inner part significantly increased during storage in both
samples. However, it took 120 days of storage for the A15 cookies to
reach the hardness value of CON cookies at 45 days.
Just after baking the thickness of the bottom crust was
surprisingly higher in the A15 cookies, although they were baked
for less than the CON samples. The values became significantly
higher in the CON cookies than in the A15 cookies after 30 days.
This can be attributed to the fact that CON samples lost more water
than the A15 samples (as previously noted), confirming the better
water-binding properties of the whey powder. Moreover, CON
cookies showed an increase of the thickness until 75 days, while
A15 cookies retained the same values of crust thickness from 30
days up to 90 days.