## 3 Results and Discussion
### Effect of Fruit- and Tree-Based Flours on the Textural Properties of Wheat Bread
#### 3.2.1 Hardness (N)  
The pressing hardness is an indicator of the resistance of baked bread to deformation, directly associated with hardness and compactness. Hardness is one of the key texture parameters affecting consumer acceptance of bread. It not only reflects the initial structure and moisture content of the crumb but also provides insight into the physicochemical changes occurring during storage, such as starch retrogradation and moisture redistribution [28]. In the present study, a clear variation in crumb hardness was observed depending on the type and concentration of flour additive. The control wheat bread exhibited a hardness of 12.01 N. Lower hardness values were recorded in breads containing horse chestnut flour (5.85-7.41 N) and 15% sweet chestnut flour (5.91 N), indicating a softer, less compact crumb structure. These effects can be attributed to the relatively high sugar content and low fibre concentration in those flours, which promoted a more open and moist crumb network. In particular, bread enriched with 5% chestnut flour exhibited the lowest values for crumb hardness (22.3 units), brittleness (31.7 units), and compactness (23.3 units), indicating a soft and airy crumb structure. These instrumental results align with panellists' sensory impressions and confirm our findings--chestnut flour significantly improved crumb softness, reduced adhesiveness, and maintained high springiness. In contrast, samples with red oak flour showed increased crumb hardness, with values ranging from 13.01 to 13.75 N for 10-15% supplementation. Similarly, bread with 15% horse chestnut flour reached 12.81 N, close to the control. This increase is consistent with the findings of [PERSON] et al. [28] and [PERSON] et al. [30], who reported increased firmness in gluten-free bread formulations supplemented with acorn flour. They attributed this primarily to the high fibre content, which enhanced water absorption and contributed to a denser structure. [PERSON] et al. [28] additionally demonstrated that the level of acorn flour incorporation has a significant impact on the evolution of crumb hardness during storage. A 20% acorn flour substitution not only provided comparable hardness on the day of baking but also effectively limited crumb firming over time. After 2-3 days, bread with 20% acorn flour remained significantly softer than all other variants, indicating improved freshness retention. Notably, the same sample was characterised by the highest specific volume and was best accepted in terms of structure and porosity. This supports the often-observed inverse relationship between bread volume and crumb hardness, which was again confirmed in our study, especially for samples with red oak flour, where a lower volume correlated with increased hardness. These findings suggest that, in addition to fibre content, tannin-rich components such as acorn flour may also influence crumb structure by interacting with the gluten or starch matrix. Although further biochemical confirmation is required, the ability of polyphenols to \begin{table}
\begin{tabular}{c c c c c} \hline
**Type of Flour** & **Proportion** & **Hardness (N)** & **Adhesiveness** & **Springiness** \\ \hline  & 5\% & 5.85 a  & \(-\)0.396 d  & 0.987 g  \\ Wheat flour + sweet chestnut & 10\% & 7.41 b  & \(-\)1.308 f  & 0.969 e  \\  & 15\% & 5.91 a  & \(-\)0.467 d  & 0.987g  \\ \hline  & 5\% & 10.77 g  & \(-\)0.222 d  & 0.967e  \\ Wheat flour + horse chestnut & 10\% & 12.81 g  & \(-\)0.996 e  & 0.966 de  \\  & 15\% & 5.38 a  & 1.029 a  & 0.999 h  \\ \hline  & 5\% & 11.65 ab  & 0.379 b  & 0.949 bc  \\ Wheat flour + apple & 10\% & 9.70 de  & \(-\)0.789 e  & 0.972 f  \\  & 15\% & 9.70 de  & \(-\)1.462 f  & 0.919 a  \\ \hline \end{tabular}
\end{table} 
Table 2: _Cont._stabilise the crumb and delay staling may represent a valuable functionality in clean-label bakery formulations. [PERSON] et al. [41] demonstrated that tannic acid affects the gluten network--while it weakens disulfide bonds, it also forms new covalent bonds with gluten proteins.