## 3 Results and Discussion
### Effect of Fruit- and Tree-Based Flours on the Textural Properties of Wheat Bread
#### 3.2.3 Springiness  
Springiness is a key textural parameter that reflects the crumb's ability to recover its shape after compression, closely related to the internal aeration and elasticity of bread. It plays an important role in consumer acceptance and is often used as an indicator of freshness and structural integrity, particularly during storage. In the present study, the control wheat bread exhibited a springiness of 0.974. The addition of selected plant-based flours significantly influenced this parameter. The highest springiness was observed in bread with 15% horse chestnut flour (0.999), followed by 5% and 15% sweet chestnut flour (both 0.987). These findings are consistent with [PERSON] et al. [44], who demonstrated that sweet chestnut flour preserved high elasticity in wheat bread, supporting its potential as a structure-enhancing additive. Our results are also aligned with [PERSON] et al. [45], who showed that increasing the level of chestnut powder (5-25%) initially enhanced springiness and cohesiveness in wheat doughs but eventually led to a decline at higher concentrations. Similarly, in our experiment, sweet chestnut flour at 10% produced lower springiness (0.969) than at 5% or 15%, indicating a non-linear response typical of fibre-rich additives. Apple flour reduced springiness at higher inclusion rates, with the lowest value recorded at 15% (0.919), likely due to the disruption of the matrix structure and moisture retention imbalance. [PERSON] et al. [46] reported comparable outcomes in gluten-free bread enriched with apple pomace powder--springiness improved at 5% but decreased significantly at 6-8% levels, suggesting a threshold effect beyond which elasticity deteriorates. Oak-derived flours (from red, sessile, and pedunculate oak) showed intermediate springiness values (0.939-0.981). Although these flours are known to increase crumb hardness and density--due to their high fibre and phenolic content--at moderate substitution levels, they did not negatively affect the bread's elasticity. This effect was previously characterised by [PERSON] et al. [12; 16; 31], who analysed the chemical composition and functional properties of all plant-based flours used in this study, including apple, sweet chestnut, horse chestnut, and oak flours. Their research showed significant differences in the content of phenolic compounds, including tannins, among the additives tested. Phenolic compounds--particularly tannins--can significantly influence the structural properties of bread. [PERSON] et al. [41] showed that tannic acid interferes with disulfide bond formation in gluten but forms other covalent interactions with wheat proteins, as evidenced by UV spectroscopy and dynamic rheometry. Texture analysis revealed that, while adhesiveness and resilience remained largely unchanged, increased hardness and chewiness were observed in breads supplemented with tannic acid. These changes suggest that tannins may delay bread staling and contribute to a denser structure. Given the natural presence of tannins in the flours used in this study--especially in oak and horse chestnut flours--their impact on bread structure likely extends beyond the water-binding capacity of dietary fibre alone. Further support for oak flour's effect comes from [PERSON] et al. [47], who showed that incorporating 5-25% acorn flour into bread formulations led to a significant increase in springiness during both refrigerated and frozen storage. The authors also found that springiness was maintained over time, confirming that acorn-enriched breads have stable and acceptable textural qualities during shelf-life. Additionally, [PERSON] et al. [48] demonstrated that the addition of acorn flour increased springiness in gluten-free bread, regardless of sourdough presence. In their study, acorn level was the primary factor influencing springiness, while storage time and fermentation had no significant effect. These results align with our findings and with [PERSON] et al.