###### Abstract
Seeds of horse chestnut (_Aesculus hippocastanum_) contain escins--a group of biologically active saponins with antibacterial, antiviral, antifungal, anti-inflammatory, and anti-oedematous properties [21]. Raw or naturally dried seeds require prolonged soaking in water or plant-based lye solutions to eliminate their characteristic soapy taste and to reduce toxicity. Alternatively, slow roasting of the seeds deactivates escins and renders them edible while preserving their nutraceutical potential [22]. These features make horse chestnut a promising ingredient in the development of functional breads with potential immune-supporting effects. The chemical composition of alternative flours may vary significantly depending on the plant species, environmental conditions, raw material maturity, and processing methods. This variability affects the levels of fibre, phenolic compounds, starch, and volatile aroma compounds [7; 23]. For instance, the detergent fibre content in acorn flour may be up to twice as high as in wholemeal flours [24], while horse chestnut may contain substantial amounts of saponins that influence the biological activity of the final product [21]. All the flours included in this study affect the technological properties of dough, such as water absorption, development time, stability, and loaf volume. Due to their limited ability to support gluten network formation, they may reduce the final bread volume [25; 26]. However, at the same time, they enrich the product with bioactive compounds exhibiting antioxidant activity, thereby enhancing its functional value and potential health benefits. The introduction of alternative flours into wheat bread production opens new possibilities for developing innovative products with improved nutritional composition and distinctive sensory characteristics. Previous studies have demonstrated that flours derived from acorns, chestnuts, and apples--particularly in the context of gluten-free products--increase dietary fibre, mineral content, and phenolic compounds, resulting in enhanced antioxidant activity [27; 28; 29; 30]. Their use aligns with the principles of sustainable processing, waste valorisation, and the growing demand for clean-label foods. The aim of this study was to conduct a comparative assessment of the technological and sensory properties of wheat bread enriched with flours derived from underutilised plant materials: red oak (_Quercus rubra_), pedunculate oak (_Q. robur_), sessile oak (_Q. petraea_), horse chestnut (_Aesculus hippocampalanum_), sweet chestnut (_Castanea sativa_), and a traditional apple cultivar (_Malus domestica cv. [PERSON]_). Unlike previous studies, uniform substitution levels (5-15%) were applied to all flour types, and a systematic evaluation was performed to assess their effects on crumb texture, crust colour, and sensory perception. The novelty of this research lies in the integrated comparison of rarely studied ingredients--particularly flours from red oak and horse chestnut--and in the use of whole seeds for flour production, including entire acorns and chestnuts. This approach offers a sustainable and nutritionally enriched strategy for bread formulation while reducing raw material losses.